One of the ways they hunted them was by stampeding them over cliffs.

Scientists thought that humans practiced communal hunting drives like this as far back as 5,000 years ago. But a recent discovery has changed that.

When constructing a new airport north of Mexico City, workers unearthed enormous bones and called in scientists, who discovered two massive pits 80 feet in diameter.

They realized the 800 bones within the pits had come from woolly mammoths. There were herds that lived in the area long ago.

They were also able to determine, based on sediment layers deposited within the pits and tool marks on their walls, that humans had dug them 15,000 years ago, by hand.

It appeared that early tribes had driven the giant beasts into them, trapping them for slaughter.

Like the Plains Indians, these hunters were resourceful with the animals, turning bones into knives and scrapers, which they used in butchering. Some of these were found in the pits.

It also appeared that many generations of humans hunted mammoths here, using this site for more than 500 years.

When they finally abandoned the pits, they left the mammoth bones artfully arranged inside, with tusks and shoulder blades encircling skulls, perhaps in tribute to the animals that fed and clothed them for centuries.

While he certainly was the first to make it a commercial success, the invention took almost a century to “come to light.”

The story begins long before household electricity.

In 1800, an Italian scientist named Volta created the first primitive battery. And one of the first things he did was connect copper wire to it, which glowed faintly.

Two years later, a different inventor ran current from a battery through carbon rods to create the first industrial bulb. But it was very bright, short lived, and not suited to household use.

More scientists, over more decades, improved filaments and used a vacuum to remove oxygen, or filled the bulb with nitrogen to extend the filament’s life.

Finally, in the late 1870’s, Edison bought a Canadian patent and formed a light bulb company.

He and his workers tested more than 9,000 filament designs. Their first successful bulbs used carbonized bamboo.

But they ultimately discovered that the rare metal tungsten, with its high melting point and electrical resistance, was the best choice.

At first, Edison’s technology couldn’t make tungsten thin enough. Later advancements wound 6 feet of ultrathin wire down to a 1-inch-long filament. They mounted it on a glass support, and the commercial bulb was born.

This design lasted nearly unchanged for over a century, only now being replaced by more efficient designs which themselves have taken more than 50 years to come to market.

It happened when the Great Depression and prolonged drought coincided, causing farmers to abandon their fields across the Great Plains.

Winds carried a billion tons of soil into the air, creating devastating dust storms that blew across the country.

The Dust Bowl era began in 1931. What ended it?

As early as 1933, the government established soil erosion camps in the region. They dispatched thousands of workers to rehabilitate millions of acres and began to teach farmers how to protect their soils.

In 1937, they stepped up these efforts, paying farmers to practice more expensive soil preservation techniques, like terracing, crop rotation, no-till farming, and planting cover crops.

Within a year, this massive effort had reduced soil loss by 65 percent. But farmers still struggled.

So the government began the Shelterbelt Project. It planted 200 million trees in a hundred-mile-wide belt from Texas to Canada, to contain soil and water and protect farms from wind.

It remains the largest environmental remediation project in American history.

Finally, in 1939 the rains returned, and the drought ended.

Wiser, crisis-hardened farmers began growing crops again, using methods to better resist droughts common to this region.

Between 1870 and 1920, settlers poured into the Great Plains, plowed under native grasses, and planted grain.

Then in 1929, the Great Depression struck, and grain prices collapsed. In 1931, a long drought set in.

Farms failed across the region. Millions of acres, stripped of grass and barren of crops, lay untended.

The fierce prairie winds carried the dry topsoil high into the sky in roiling storms of black dust that pummeled farmers and buried buildings.

In 1933, a storm like this came nearly every week.

In 1934, the dust clouds expanded to cover the Midwest.

In 1935, a blizzard of hot, black soil raced across the country at 100 miles an hour, cutting visibility to three feet and blanketing Washington, D.C.

By then, nearly a billion tons of fertile topsoil had been carried off the Great Plains.

The human toll was staggering. More than 3 million people abandoned their farms and businesses and left the Plains, penniless.

Those who stayed suffered: respiratory diseases from breathing dust, hunger so severe they had to eat tumbleweeds.

Infant mortality soared and birth rates dropped to the lowest in U.S. history.

What finally ended the Dust Bowl? We’ll see, in our next and final installment of this story.

The Dust Bowl—which refers both to this event and the place where it happened: some 100 million acres in Kansas, Colorado, Oklahoma, New Mexico, and Texas.

This area normally sees just 20 inches of rain a year. High winds from the Rocky Mountains roll across it. Summers bring scorching heat; winters bring Arctic blasts from Canada.

Explorers called it the Great American Desert and avoided it.

But in the late 1800s, agents from the government, eager to push development westward, rebranded it “the Great Plains.”

Anyone with an $18 filing fee could stake a homestead. People came in droves and found an ocean of native grasses.

These grasses had developed to withstand the prairie’s harsh conditions. Over thousands of years, they created the topsoil, held it in place against the wind, and trapped moisture to withstand periodic droughts.

But to the inexperienced farmers, it just looked like grass. They burned it or plowed it under, and planted wheat and other crops.

Grain production soared and the expansion seemed a success. Over the next 50 years, millions more settlers arrived.

Then, in 1929, the Great Depression hit. Grain prices collapsed. Worse, in 1931, the rains stopped.

What followed was a disaster of epic proportions, which we’ll cover in our next installment on the Dust Bowl.

Water has many rare properties, some of which we’ve covered on previous episodes.

But this property, its blueness, is unique to water and goes right to its core. It’s the only molecule in the universe that vibrates a color.

How is that?

The water molecule is made up of two atoms of hydrogen and one of oxygen.

The hydrogen atoms are very lightweight, but their bonds are very strong. Imagine ping pong balls connected by metal springs. It doesn’t take much to start water molecules vibrating.

In basic terms, light itself is vibrating electromagnetic energy. Different colors have different vibrational frequencies.

Water molecules vibrate fast enough to reach the lower frequencies of visible light, where they absorb red light, so we see the blue light that remains.

This effect is too faint to notice in your glass of water. But it’s already visible in a bathtub or swimming pool, and gets more pronounced when the effect is amplified, as light passes through more and deeper water.

Scuba divers know this well. Past a certain depth, blue becomes the only color—till they turn on a flashlight, which reintroduces full-spectrum white light, and all the colors appear again.

There are other molecules that vibrate, but none that can reach into the visible light spectrum. Only water is true blue.

But you may be more amazed to know that the returning butterflies are the great-great-grandchildren of the butterflies that left.

Here’s how that works:

The first generation of monarchs leaves Mexico in the spring, pausing to breed and lay eggs as they fly northward.

Their eggs hatch into caterpillars, which eat for two weeks, then metamorphose into butterflies. In four weeks, they too are flying northward.

As the first generation dies, the second generation will fly on, farther north, pausing only to lay eggs of their own. Eventually they too will die, and be passed over by their offspring.

This third generation will finally reach Canada, where they’ll lay eggs.

But the fourth generation that comes from them will be genetically different.

The shorter days and colder temperatures cause these butterflies to develop much larger fat stores, making up a third of their bodies.

And their reproductive organs remain undeveloped—since their purpose is not to breed, but to fly.

Before winter arrives, they’ll make the entire 3,000-mile journey to Mexico—where they’ll seek out the same mountaintops as their great-great-grandparents.

They’ll roost in the same fir trees, congregating in huge masses to hibernate through winter.

In spring, their reproductive organs develop, and they’ll begin their own flying, mating, egg-laying journey, to start the amazing monarch relay, all over again.

In a few places, like Iceland, geologic features allow this heat to come close to the surface. Here, it often turns groundwater to steam.

For a century, Iceland has been tapping into this naturally occurring steam and using it to heat the homes, streets and sidewalks of Reykjavik. Or to run power plants to make electricity.

Now, Iceland is trying to take it a step further. Scientists are drilling experimental wells, nearly 3 miles into the earth, to try to tap into superheated water.

At what’s called supercritical temperatures, above 750 degrees Fahrenheit, water and steam merge into a single supercritical fluid, which behaves differently than either.

A typical Icelandic geothermal steam well produces the equivalent of 5 megawatts of energy. A supercritical well could produce 10 times that.

This means that just three or four wells could heat an entire city.

Of course, this is a very challenging prospect. At such high temperatures and pressures, supercritical fluid is very hard to handle.

Iceland shut in its first successful well after a valve failure.

But the massive amount of energy on tap could make this a promising energy source—in those rare, lucky places where supercritical water is near enough to the surface to access.

That flood was caused by an ARkStorm. The A R in Ark stands for Atmospheric River.

Atmospheric rivers are layers of water vapor that form in the tropics and circle the globe.

They’re very large—up to 2 miles high, 500 miles wide and 5,000 miles long. Each can carry 15 times the flow of the Mississippi River.

Atmospheric rivers are always forming, and always flowing—until they hit something like a mountain range, that forces them up into the colder atmosphere, where they condense into rain.

In this way, they provide 90 percent of the rain in the mid-latitudes, and up to 50 percent of California’s.

But they can also bring extreme floods.

Sedimentary records show this has happened in California 10 times in the last 2,000 years, suggesting that California is due for another one.

Since the 1861 flood, the state’s population has increased more than 100-fold. Millions of people now live in areas vulnerable to droughts, fires and floods.

Scientists predict an ARkStorm could flood a quarter of California homes, cause one and a half million people to evacuate, and leave almost a trillion dollars in damages.

A California super flood is as likely as a super quake but could be three times more devastating.

In 1861, California had been in drought for 20 years.

Most of the state’s residents lived around San Francisco and in the Central Valley.

Ranchers there had been praying for rain for two decades. In November, they finally got it.

First, winter came early, bringing heavy snow to the mountain range that bounds the valley.

In December, temperatures rose, the snow melted and drained into the valley, saturating the soil.

Then the rains came—and didn’t stop for 43 days. Wave after wave of storms rolled in from the Pacific, bringing more than 10 feet of rain and snow.

Creeks became rivers, sweeping entire towns away. Rivers jumped their banks and cut new channels.

But much of the water was trapped in the Central Valley, which became an inland sea, stretching 300 miles north to south, in places 60 miles wide.

It took six months for this inland sea to evaporate and percolate into the ground. But the flood had destroyed a quarter of California’s taxable property and almost forced the state into bankruptcy.

It also wiped out nearly 1 million livestock animals, prompting the Central Valley to move away from ranching to become the agricultural powerhouse we know today.

Superstorms like this come along every 150 to 200 years, and we’ll talk more about them on a future EarthDate.

All animals need it for the function of blood, organs, muscles and nerves. Carnivores get it from eating other animals. Herbivores get it from salt licks and minerals in groundwater.

For millennia, humans have used salt to preserve meat—and still do today. This works because salt, in abundance, kills bacteria.

When we pack meat in salt, it draws water from the cells. Water naturally moves across cell membranes to try to reach an equilibrium of saltiness on both sides of the membrane.

This process dehydrates the meat, making it inhospitable for bacteria and parasites, which need water to live.

Culturally, salt has been equally important.

Salt-preserved meat and fish were crucial to our exploration of the globe, feeding sailors as they crossed oceans, and sustaining remote communities.

Wars were fought over salt, and access to it could influence the outcome.

As recently as the American Civil War, Union troops captured Confederate salt mines to limit their food supply and force them to the coasts to get salt—where they could be more easily attacked.

Settlers in the West often followed game trails to and from brine springs or salt outcrops. These became cattle trails, then wagon paths, then roads, sometimes even the highways of today.

Salt has literally shaped the course of human history.

Floating rocks, some the size of basketballs, as far as the eye could see. Imagine their amazement!

Turns out the rocks were pumice, which was extruded by an undersea volcano near the island of Tonga.

Pumice is molten rock filled with gas bubbles, ejected at high pressure like whipped cream from a can. When it hits the seawater, it hardens instantly, trapping the gas within it, making a rock that’s lighter than water.

The pumice then floats to the surface where it forms huge rafts of rocks, from pebble size to much larger.

They’ll float until wave action breaks up the rocks as they grind against each other, or they get waterlogged and sink.

These rock “rafts” form only about twice per decade but can be enormous.

In 2012, one formed off the coast of New Zealand that was 300 miles long.

The raft from Tonga was the size of Manhattan and was floating toward the Great Barrier Reef.

The surface of pumice is rough, full of craters and crevices, making it perfect for mollusks, corals and other sea creatures to attach themselves for the ride.

Scientists think that pumice rafts like these have helped life-forms cross open oceans and start new colonies in new places. Much the way humans did on rafts of our own making.

An adult pangolin is 3 to 5 feet long and eats some 70 million ants and termites a year, using a tongue that’s longer than its body, covered in sticky saliva.

It burrows into termite mounds and anthills and can close its ears and nostrils to keep angry ants at bay.

That may sound like an anteater or an aardvark. Except, the pangolin is completely covered in scales. It’s the only mammal that has them.

These scales are made of keratin, just like our fingernails. A single pangolin could have more than a thousand, making up 20 percent of its body weight.

Pangolins roll into a ball when threatened—the sharp edges of their scales providing extra protection, even against lions.

But that’s not enough to keep human predators away.

The pangolin’s scales are valued in Asian folk medicines, even though they’ve been proven to be no more medicinal than an old toenail.

Their meat is eaten in Asia as a delicacy. Even their blood is considered an aphrodisiac.

So, poachers catch and kill them, which has made all eight species critically endangered or vulnerable.

In the last 10 years, customs agents have confiscated literally tons of pangolin scales, which came from more than 1 million animals.

World Pangolin Day is February 15. You probably don’t buy pangolin products yourself, but raising awareness for this remarkable, gentle animal can support its protection.

But once a century, a house-sized meteor makes contact—and explodes in the air with devastating results.

In 2013, one such airburst occurred in Russia.

The Chelyabinsk meteor broke apart miles above the surface, with 30 times the force of the Hiroshima atomic bomb.

It blew out a million windows over 200 square miles and injured 1,600 people.

In 1908, near the remote Russia-Mongolia border, a larger airburst occurred.

Scientists who arrived on the scene found it had flattened 80 million trees over 800 square miles.

Events like this happen every millennium, and in 1700 BC, there was an even bigger one.

North of the Dead Sea, in what is now Jordan, 50,000 people were vaporized in an instant.

A flash of extreme heat, over 7200 degrees Fahrenheit, disintegrated houses, melted sand and stone, and turned pottery to glass.

A tidal wave of boiling saltwater swept inland, poisoning the soil. The area, which had been continuously inhabited for 2,500 years before that, lay desolate for 600 years after.

Since the Chelyabinsk meteor in 2013, NASA initiated a program to identify and track objects within 5 million miles of Earth that could enter our atmosphere and cause an airburst.

What can you do to avoid getting trapped—and to escape if you do?

It starts by knowing where quicksand forms and what it looks like.

Quicksand is just super-saturated sand. Normal wet sand is about 25 percent water; quicksand is more than 70 percent.

Quicksand can form on beaches, tidal flats, riverbanks or near springs—anywhere the ground is saturated with water.

In those places, look out for sand that’s spongy or rippled in appearance, and check suspicious areas with a stick.

Quicksand looks solid, and if you were to place something or even step lightly upon it, it may support you.

But step firmly and the quicksand will liquefy, and you’ll sink. Because humans are buoyant, we typically won’t sink below the waist or mid-chest.

But once the sand grains are out of liquid suspension, they too will sink, and compact around your legs, trapping you.

The more you struggle, the more sand will liquefy and sink, and the more trapped you’ll become.

The key to getting out is to remain calm.

Lie back in slow motion. Wiggle your legs in tiny movements, which will slowly let water in to loosen the compacted sand. Then gradually recline to float on the surface.

Once free, you can slowly crawl or swim to the edge and roll onto solid ground.

In Australia, where the trees originate, they’re about to become more popular because they may lead miners to gold.

In Australia’s dry climate, eucalypts send roots down hundreds of feet looking for water.

In gold mining areas, scientists have found microscopic gold flakes, thinner than a human hair, in the tissues of their leaves and on the waxy residue that coats them.

They wondered if blowing dust could have carried gold particles onto the trees or if perhaps their deep roots could have drawn up trace amounts from far below the surface.

They conducted experiments, growing eucalypts in sterile environments, giving them gold-laced water. And sure enough, gold appeared in the foliage.

They realized that the gold is probably toxic to the trees, which send it out to their leaves where it can be shed.

The scientists analyzed eucalyptus trees in other parts of Australia but found very little gold. Clearly, trees in gold-rich regions were mining it themselves!

Before we get too excited about processing eucalyptus leaves for gold, it would take 100 trees to produce enough for a wedding band.

Scientists do believe, however, that searching for trace amounts in eucalyptus leaves could be a low-impact way of prospecting for gold in the future.

Each spelled the end for millions of species—and the beginning for millions more that evolved to take their places.

On earlier EarthDates, we talked about the asteroid that smashed into Earth, ending the reign of the dinosaurs while opening the door for mammals.

But there was an earlier event that appears to have created the same opening for dinosaurs themselves.

Around 250 million years ago, dinosaurs made up only about 5 percent of animals on Earth. 

Then a massive series of volcanic eruptions filled the atmosphere with carbon dioxide, which triggered dramatic global warming and extreme global rainfall.

The rain caused floods across the planet for many thousands of years. Floods alternated with periods of drought for 1 to 2 million years, to create an era so severe it earned its own geologic name: The Carnian Pluvial Episode.

It stressed all life on Earth, plants and animals, and removed many species that were poorly equipped for the harsh conditions.

By 2 million years after the Pluvial Episode, dinosaurs, who were better adapted for these conditions, exploded in population and variety, with new species filling empty environmental niches.

What happened for the dinosaurs, then happened to the dinosaurs—and it will happen again. In this way, life on Earth renews itself. 

Amundsen’s crew left 20 days before Scott, using sled dogs.

Scott’s team took a different route, using motorized snow tractors, hoping to speed their passage.

After 77 days, Scott and his men finally reached the pole—only to find that Amundsen had beat them to it.

With great disappointment, they turned back to their ship … when disaster struck.

The temperature plummeted as the Antarctic winter arrived early.

In their journals, they recorded temperatures below -40o Fahrenheit.

Weather kept their base team from provisioning their return depots. Out of fuel, they had to pull sleds with their tents and gear.

In the extreme cold, the ice was no longer slippery—we talked about this in a previous EarthDate.

A layer of water less than one-billionth of a meter thick occurs on the surface of ice down to -36o Fahrenheit.

Below that, the water molecules become pinned to the ice and they no longer slip.

This meant that Scott’s sleds no longer slid, slowing their progress and doubling their exposure to the severe cold.

One by one, the men got frostbite and could no longer travel. Out of options, they made their last camp, wrote farewell letters, and waited for the end.

A trip cut tragically short by the not-so-slippery properties of ice.

But before she can get up to speed, and friction can melt the ice, it’s still slippery enough for her to start her glide. Why is ice so slippery?

In the 1800s, scientist Michael Faraday conducted experiments to show that ice, even well below freezing, has a very thin layer of water on its surface.

But the technology to see this layer did not exist. Nor did the scientific understanding to prove that it was there.

It would be more than 100 years before scientists could finally see Faraday’s water layer using X-ray imaging. And still later that they could measure it.

Turns out this thin layer is very thin indeed—thousands of times thinner than a sheet of paper. In fact, it’s just a couple of molecules thick.

When water freezes, its molecules interlock tightly to create the crystalline structure of ice, held together by four hydrogen bonds.

But the molecules on the surface of ice can only bond to the molecules just beneath them, with just three hydrogen bonds. This won’t allow a stable crystalline surface.

This strange, disordered molecular state of water on the surface of ice will persist down to -36o Fahrenheit.

But if the temperature goes below that, ice will no longer be slippery—sometimes with disastrous results, which we’ll talk about on another EarthDate.

The first, of course, is Earth’s rotation, turning day to night and back again.

To complete this cycle, Earth rotates at 1,000 miles an hour, counterclockwise.

Not all planets spin this way. Venus rotates the opposite direction, and Uranus spins at 90 degrees to its orbit.

But pretty much everything in the universe spins.

The second cycle of course, is Earth orbiting the sun. The Solar System began as a cloud of dust and gas spinning around the sun 4.6 billion years ago, and should keep spinning for a few billion years more.

This rotation of Earth around sun is even faster: 67,000 miles an hour, and it takes 365-and-a-quarter days. This was recognized and set into a calendar by the Romans, but they overlooked that extra quarter day.

Meaning that, by the late 1500s, the calendar had drifted 10 days off. At that point, Pope Gregory added a leap day every 4 years, and the modern calendar was born.

Our Solar System is moving, too, and faster still. It’s in the Orion arm of the Milky Way galaxy, which orbits a supermassive black hole at 600,000 miles an hour.

And the black hole is spinning, too, even faster—more than 1,000 times a second.

So, if the New Year has your head spinning, well, now you know why.

They can fly over the tundra at 50 miles an hour, covering more than 20 miles a day.

Their annual migrations span 3,000 miles, the longest of any land animal.

And they’re spectacularly adapted for that life:

Their eyes change color depending on the season. In their summer above the Arctic Circle, with nearly 24 hours of sun, their eyes turn gold, to reflect the harsh light.

In the dark months of winter, their eyes turn blue, to let in as much light as possible.

Their eyes also can see ultraviolet light.

This makes the snow even brighter, but against it, some important things appear black: The fur of predators, who might otherwise be camouflaged. And lichen, the reindeer’s primary winter food.

What their eyes can’t see is red. Like many mammals, they’re red–green colorblind; both colors appear brown.

While this would have made it hard to follow Rudolph’s nose, their noses are pretty amazing in their own right. They’re lined with capillaries, to warm the frigid air before it enters their lungs.

They’re also the only deer species where both males and females grow full antlers. The males’ drop off after mating season ends in November. But the females’ stay on through winter, into the spring calving season.

This means that if Santa’s reindeer do, in fact, have antlers on Christmas Eve, they’re all females.

So, while it’s very unlikely you’ll get caught in one, here are a few safety tips, just in case.

Avalanches happen when a slab of unstable snow breaks off from the layers beneath it. If you’re on top of that slab when it happens, ski or run for the sides.

Same thing if you’re in its path. Avalanches can reach 80 miles an hour in 5 seconds, and top 120 miles an hour. You won’t be able to outrun it, so head for the sides to get out of the way.

If you do get caught in it, swim against the snow to try to stay on top. Humans are heavier than the moving snow, so we tend to sink into it.

When the avalanche stops, there will be a brief period when the snow is still loose. If you’re disoriented, spit. That’ll tell you which way is down. Then try to dig your way up and out.

If you can’t, carve a breathing space, as large and as quickly as you can.

The weight of the snow will soon compress and harden it, restricting your movement. Try to remain calm, to conserve your energy and your oxygen.

The most important tip is to be prepared before you head into the mountains. Take an avalanche beacon, which can transmit a signal to rescuers.

Let friends know where you’re going. And check with local authorities to avoid avalanche areas in the first place.

Because the best way to survive an avalanche is to not get caught in one.

The first and most widespread is low-temperature heat—found everywhere, just below the surface—which can be used to maintain a constant temperature in buildings.

The second is much rarer: extreme heat found near volcanoes and fault zones, where high temperatures from deeper within Earth come close to the surface. These can produce steam to run electric power plants.

We’ll talk about both these types on future EarthDates.

The most commonly used geothermal energy, though, comes from hot springs—where rainwater seeps down into the Earth to reach deeper heat sources like magma chambers, then rises back out.

We’ve bathed in, and built around, them for thousands of years, often assigning them religious significance or health properties.

Romans constructed hundreds of baths at natural hot springs across Italy, often featuring elaborate architecture and plumbing systems, and they became an integral part of society—places to conduct business, politics, or courtship.

When the Romans conquered Europe, they expanded upon baths that earlier peoples had built in France, Hungary, Germany, and England.

Today, bathers still enjoy these and other hot springs. While more modern uses include heating houses, pasteurizing milk, and melting ice off streets.

The tuatara is a 2-ft-long resident of New Zealand. It may look like a lizard, but it diverged from modern lizards and snakes 250 million years ago, and it’s quite a different animal.

To start, it’s adapted to cold weather. The tuatara can thrive when its body temperature is just 40 degrees Fahrenheit.

It hibernates through winter, breathing as seldom as once per hour.

And it does everything else slowly, as well. The tuatara doesn’t reach sexual maturity till the ripe age of 35. Females produce eggs only once every 4 years.

Their babies hatch with a third eye on top of their heads, able to register light but not images. Its exact purpose is unknown, and after 5 years, the tuatara’s skin grows over it.

Its teeth are unusual, too. Two top rows overlap a single bottom row and saw together to eat their food. However, they’re not really teeth but bony projections from the jaw.

When the tuatara reaches old age, which could be well over 100 years, its teeth have completely worn off. And it has to switch to a soft food diet of worms and larvae.

The tuatara, sometimes called a living fossil, has even appeared on New Zealand’s money.

In nearly every way, this remarkably persistent animal is a “one of a kind.”

Homo sapiens evolved around 300,000 years ago, when there were at least three other species of the genus Homo on Earth. By 40,000 years ago, we were the only one left.

But at least we have great ape cousins in the hominid family. There are other species on Earth that are even lonelier, the last branches of their family trees.

Koalas live only in Eastern Australia—the only species and the only genus in their families. Their closest living relatives are another unusual Australian, the wombat, which they diverged from 35 million years ago.

It’s thought that koalas’ highly specialized diet is the reason they branched off. They’re adapted to eat eucalyptus leaves—and only eucalyptus leaves. Which happen to be high in toxins, high in fiber, and low in calories.

To handle this poorly nutritious diet, they developed special teeth, special stomachs, and special livers. And sleep nearly 20 hours a day to process it through their systems.

Aardvarks have been lonelier longer. Their closest living relative is the African elephant, separated by 80 million years. They may look like South American anteaters, but that’s because they evolved to eat the same diet of ants and termites.

There’s one animal even lonelier, surviving almost unchanged since the dawn of the dinosaurs. But we’ll save that for another EarthDate.

Puzzled, they wondered if they’d found isolated pockets or a continuous aquifer.

Thirty years later, a new technology arrived to help answer this question. Electromagnetic imaging could read the electrical conductivities of subsurface fluids to identify them.

Saltwater is very conductive. Oil and fresh water are not.

They surveyed the same area, and what they found astonished them: a freshwater aquifer 600 ft thick, stretching from New Jersey to Massachusetts, extending more than 50 miles out from the shore.

Geologists set to work to determine where it had come from.

At the peak of the last Ice Age, much of Earth’s water was locked up in continental ice sheets, causing sea level to drop 400 ft—exposing most of the Atlantic continental shelf.

As the climate naturally warmed and the ice receded, meltwater flowed for thousands of years into sedimentary rocks of the continental shelf, charging them with water.

When the rate of glacial melt slowed over the last few thousand years, sediments deposited on the seafloor sealed the aquifer beneath them.

This huge reserve of Ice Age glacial melt could one day supply fresh water to the Eastern U.S.

And it has led scientists to probe other continental shelves, to see if they, too, hold large stores of fresh water.  

It erodes mountains, slowly leveling them over millions of years.

It fills aquifers, and when those are drained too much or too rapidly, the surface of the land above them can sink.

But another way water can shape the land is simply by weighting it down. And when billions of tons of water evaporate from a mountain range or inundate a city, the land can rise or fall.

California suffered a severe drought from 2011 to 2015. Scientists studying its effect on the landscape surveyed the Sierra Nevada range using sophisticated GPS.

This technology can detect changes in elevation of just 1 mm. It revealed that the mountain range, which had lost 10 cubic miles of water to evaporation, rose 1 inch during the drought.

Conversely, researchers studying the effects of Hurricane Harvey found that it dumped 20 cubic miles of water on Texas and Louisiana that weighed more than 100 billion tons.

This caused the Earth to sag beneath its weight, up to an inch depending on the amount of floodwater.

They found that they could even trace the path of the storm over the land by following the surface depressions left behind it.

As Harvey’s floodwater drained into the Gulf of Mexico, GPS measurements showed the surface slowly rebounding to pre-flood levels.

Deciduous trees, whose broad leaves are too delicate to survive the freeze, pull their sugars back into the body of the tree and let their leaves die and fall, as we explored in a previous EarthDate.

Coniferous trees—like pine, spruce, fir, and cedar—have a few different solutions.

First, their “leaves” are needles, adapted to the cold. They’re thick, have less surface area, and are coated with a waxy substance called cutin, which traps moisture within them.

So that the needles are not damaged by freezing, as cold weather approaches, water within their cells moves to spaces between the cells and concentrates with sugar to lower its freezing point.

The whole tree, in fact, produces a protein that acts like antifreeze, binding ice crystals and causing them to form less-damaging hexagonal shapes instead of their traditional needle form.

This system works so well that evergreen needles can stay on trees through several winters. They fall off only due to age and are quickly replaced by new needles.

By retaining their leaves, evergreen trees also retain their nutrients. Preserving their nitrogen, potassium, phosphorus, calcium, and magnesium allows them to survive in extreme environments, like high-mountain soils that may have little of these minerals.

And staying green throughout the late fall and early spring allows them to conduct photosynthesis and produce sugars when deciduous trees can’t.

It has to do with the properties of sunlight and Earth’s atmosphere.

Sunlight is made up of many wavelengths of visible light. Combined, we see them as white. But individually they’re a rainbow of colors, from violet and blue to orange and red.

When sunlight enters Earth’s atmosphere, it collides with molecules of oxygen, nitrogen, and other particulates, which scatter the light into different colors.

Violet and blue light have the shortest frequencies and the most energy, so they scatter the most. Much of the violet light is absorbed by the upper atmosphere, but blue light is reflected throughout the atmosphere, giving us a blue sky.

Once near the surface, blue light has been scattered and reflected so much, it recombines with other colors into full-spectrum white light.

When the sun nears the horizon, sunlight passes through much more atmosphere. That longer journey scatters and eventually filters out more of the blue light, leaving the longer-wavelength orange and red light to reach our eyes.

But it’s not this way everywhere. On Mars, the atmosphere is mostly CO2 and filled with iron-rich dust, which scatters the red light, turning the sky there…red.

Except at sunset, when the longer trip through the Martian atmosphere scatters and filters so much red light that blue light passes through—making the sunset…blue!

To keep their ships stocked with fresh water, sailors have relied on innovation and technology for centuries.

Early on, they realized they could funnel rainwater from their sails into storage—once the rain had washed away the ocean spray.

Greek sailors then discovered they could hang sheep pelts in the cool night air to absorb water vapor, then wring them out in the morning for a wool-flavored drink.

The earliest European sailors used barrels laced with alcohol to keep algae from growing.

Whenever a ship reached land, replenishing its fresh water was usually the most important task.

By the 1700s, inventors had created distillation plants that used a heat source to boil seawater. When it converted to steam, it left the salt behind. The vapor would then condense again into pure distilled water.

Distillers were used until 1980, when they were replaced by reverse-osmosis systems that use membranes to purify and desalinate water.

Today, navy fleets of about 50 ships have the capacity to desalinate more than a million gallons of water a day.

Cities with large naval bases, like San Diego, are looking at ways to use their fleets’ desalination capacity to supplement their municipal water systems in times of drought and other emergencies.

Near the end of the last Ice Age, just 20,000 years ago, continental ice sheets covered 25 percent of Earth’s landmass, pushing down on Earth’s surface with as much as 150 tons per square foot of pressure.

This depressed the surface and pushed up the land around the perimeter.

During the last 15,000 years, the Ice Age ended and glaciers have naturally retreated to cover only 11 percent of the land surface today.

And just like a rubber ball, the Earth’s surface has been rebounding—very slowly.

Areas that were depressed by ice are rising. Canada, Scotland, and Scandinavia all have risen 4 to 6 inches over the past century.

Areas that had bulged outward at the edge of glaciers are now sinking, back to pre–Ice Age levels, around 4 inches per century.

This can be seen in southern England and Ireland and the northern and middle U.S., including many cities like Chicago, Milwaukee, and Cleveland.

In low-lying near-coastal cities like London and Washington, D.C., falling land levels combined with rising seas from continued glacial melt are making those cities more prone to flooding.

We can expect rising and falling landmasses, and associated shoreline changes, as Earth continues its slow motion Ice Age rebound.

Once the egg hatches and the salmon begins to grow, it moves downriver, eating larger prey, taking in iron from its environment and its food, to synthesize more magnetite to store in its body—particularly in the sinus bones within its skull.

Once it’s large enough to enter the ocean, its scales change from green and brown to the silver and gray of the open sea.

The magnetite in its nose begins to line up into chains that can detect and respond to the magnetic fields of the Earth.

The salmon is developing its magnetoreception.

In the ocean, it feeds on fish and krill, ingesting more iron, storing more magnetite, traveling thousands of miles—up to 18 miles a day—over the next few years, guided in the dark waters by its three-dimensional magnetoreception, sensing not only direction but intensity and inclination of the magnetic field.

When it’s time to return to its home river, magnetoreception is aided by another sense in its nose: smell.

The salmon can detect just a few parts per million of its birth river in ocean currents and follow them home. Once there, it will mate and die.

Nutrients and minerals from its body will return to the stream to nourish future salmon, who will make their own magnetite for their own magnetoreception, to guide their own miraculous journey, handed down across thousands of generations.

Three things: leaf pigments, the weather, and the length of the days, called the photoperiod.

To protect themselves from freezing, broad-leafed trees in temperate areas must harvest the sugar from their leaves for the winter.

This starts when shorter days signal trees to slow the production of chlorophyll.

As photosynthesis uses up the remaining green chlorophyll, yellow pigments that are always present in the leaves show through.

Mild sunny fall days will rapidly process the chlorophyll and leave bright golds, while rainy or hot days will make for more muted colors.

Cooler nights soon trigger the production of red and purple pigments, which are thought to act as a sunscreen, further slowing photosynthesis.

These red colors are more abundant in healthier plants and may serve to warn insects away, toward weaker plants.

Eventually, the last sugars are drawn from the leaves and into the branches, trunk, and roots of the tree for storage during the winter.

Cells form at the base of the leaf, making it more likely to fall off, and at the twig end, like a scab, sealing the twig off from outside elements.

Only the vascular bundles connected to the veins of the leaf hold it to the tree.

When the leaf finally falls, its remaining nutrients are recycled into the soil to be used by the tree for future growth.

Meanwhile the bundle scar left on each twig becomes a bud for a new leaf in the spring—when the tree will use its stored energy to grow a new crown.

It alternates regularly between these about every 11 years.

During solar maxima, sunspots increase but so do solar flares, making these times of increased irradiance.

Higher-than-normal electromagnetic radiation causes geomagnetic storms on Earth that impact GPS systems, satellites, and power grids.

Charged particles emitted can be hazardous to astronauts and spacecraft electronics.

More X-rays and extreme UV radiate toward Earth, but most are absorbed by the outer atmosphere, called the thermosphere.

The increased energy causes the thermosphere to expand, interfering with the orbit of satellites.

Conversely, during solar minima, solar flares and charged particle emissions are rare.

This is generally good news, since it means fewer geomagnetic storms and lower solar radiation risk.

However, there’s less solar energy to form ozone in the middle atmosphere, which allows more sunburn-producing UVB to reach Earth’s surface.

And reduced solar wind means that more cosmic rays can reach Earth.

Both solar states pose unique challenges. But for the most part, our atmosphere reacts to the increasing or decreasing energy and continues to protect us.

For more than 4 billion years, hydrogen has fueled our sun, a nuclear fusion reactor that fuses hydrogen into helium to light up our solar system.

Hydrogen has also fueled our rockets. It’s very lightweight, a huge advantage for space travel. Under extreme pressure, or at extremely low temperatures, it becomes liquid.

Without a spark and an oxidizer, liquid hydrogen is stable. So rockets also carry liquid oxygen and an ignition source. Once lit, hydrogen packs a serious punch, burning at more than 5,000 degrees Fahrenheit.

Hydrogen may one day power our earthbound transportation, too. In most fuel cells, hydrogen is forced through a membrane. It splits off an electron as electricity, which can run an electric motor to propel a vehicle.

To fill the tank of a fuel-cell car, hydrogen has to be highly compressed—but in that state, it contains three times the energy, pound for pound, as gasoline.

And when processed through a fuel cell, the only emissions are water vapor.

On Earth, hydrogen doesn’t often exist in a pure gas form. But it can be separated from water by electric current.

Whether used in cars, rockets, or even fusion reactors, this essential element could, and probably should, play an ever-more-important role in powering the world.

Take for example, our lower leg. Our foot has 26 bones, and our ankle, 7. Far more moving parts than needed to walk or run, making us much more prone to injury.

How did this happen?

Well, we evolved from earlier hominins who evaded predators and found food in the trees.

Those ancestors needed a grasping foot, like a chimpanzee’s—with a big toe like an opposable thumb and a flexible ankle like a wrist.

As we climbed down from the trees and onto land, our feet had to evolve.

The foot and ankle became rigid to make a propulsive lever. The arch developed as a shock absorber. The big toe moved forward in line with the others.

This worked well enough. Even though they’re built on an old structure more like hands, our flawed feet carried us into the modern day.

Now, look down at your feet and imagine a different design: a streamlined lower leg wrapped in ligaments, not muscles; a fused ankle ending in one or two large, simple toes with just one bone in each.

Sounds weird—but this is the structure that propels ostriches and horses to speeds over 40 miles an hour, absorbing more stress while using comparatively less energy.

Different structures, borne from different evolutionary pressures.

We’ll look at other curious cases of human evolution in future EarthDates.

Of these, geographic north, the tip of Earth’s axis, defines latitude and longitude on our maps, while magnetic north is what compass needles point toward.

Unfortunately, geographic north and magnetic north are not in the same place. So the north of our maps and the north of our compasses don’t match.

The difference between them is called declination.

To complicate matters, declination varies depending on your location. Compass navigations have to be offset by the declination of that particular spot to make them accurate to the map.

Now for the real curveball: magnetic north is always moving!

It’s based on Earth’s magnetic field, which is created by turbulent currents in Earth’s molten metal outer core as they swirl around its solid iron inner core.

Shifting currents mean the magnetic field is always moving. Which means magnetic north is always changing. And declinations around the world are always adjusting!

We can see this effect all around us. Streets and walls built to compass north a few centuries ago may now be off by several degrees.

Runways, which are named by their compass orientation to help pilots navigate them, periodically have to be renamed when the declination of that spot changes.

To keep planes and ships safe, scientists track the movements of magnetic north and the constantly changing declinations and keep them updated every 5 years.

The one we most commonly think about is the Geographic North Pole—the tip of the axis that the globe spins around. It’s in the middle of the Arctic Sea, on pack ice, above more than 2 miles of water.

During the summer, when the pole is tilted toward the sun, it’s 24-hour daylight. In the fall, the sun finally sets—once, and only once, per year. That brings on 6 months of night, until springtime, when the once-annual sunrise starts another 6 months of day.

The North Magnetic Pole is slightly to the south. This is where Earth’s magnetic field, which springs out of the ground at the South Magnetic Pole, dives back into the ground.

Its exact location, however, is constantly changing, because Earth’s magnetic field is always changing.

Today, magnetic north is moving about 34 miles a year, gradually traveling toward Siberia.

Finally, there’s the North Geomagnetic Pole—the northern axis of the magnetosphere, the magnetic shield that protects us from solar winds.

If you imagine the magnetosphere as a ball around a bar magnet, with the bar running through Earth, this pole would be the positive end. It’s currently 700 miles south of the Geographic North Pole but also always traveling.

With three dark places to look in the dead of winter, and two of them moving, it’s a wonder Santa ever makes it home.

And its colossal size is an evolving mystery.

Early geologists could not believe such a comparatively small river could carve something so immense. So they looked more closely…

And discovered that a myriad of geological processes have combined to form the canyon through time.

One of the more dramatic is giant floods, vastly larger than anything we see today.

Floods from melting ice sheets. From enormous lakes overflowing their boundaries. From lava dams forming within the canyon, which held back water until they failed spectacularly.

Floodwaters can carry hundreds of times more rock material than a normally flowing river.

These superfloods likely dragged house-sized boulders through the canyon, battering the softer lower rock layers until they collapsed, bringing all the rock above them crashing down, to be carried away in the next superflood.

Geologists suspect these processes happened repeatedly in several smaller canyons, which finally linked together to become the Grand Canyon we know today.

In 1919, the U.S. Congress and President Woodrow Wilson set aside the canyon as a National Park for, as Theodore Roosevelt had said years earlier, “your children, your children’s children, and all who come after you.”

If you haven’t seen it with your own eyes, you owe it to yourself to go and be awed by the Grand Canyon.

In World Wars I and II, homing pigeons could operate faster than wires could be strung and farther than the troops’ radio signals.

In one famous account, an infantry unit trapped behind enemy lines released three pigeons, but all were shot down. Despite her injuries, one took flight again and successfully delivered her message to save the soldiers.

Military surgeons were able to save her life, and she received a French medal of honor and a visit from U.S. General John Pershing.

Long ago, homing pigeons were bred from normal rock pigeons, which could find their home from as far as 1,000 miles away.

Eventually, handlers realized they could train them to fly between points, by putting their feed at both spots. The birds could even adapt if one of those locations moved.

This remarkable power of navigation is partly based on magnetoreception, as we discussed in an earlier EarthDate.

But they may also be following anomalies in Earth’s gravitational field, infrasonic sound waves, and scent trails in the atmosphere.

The only sense they use that we can experience ourselves is visual. Some studies suggest the birds read surface landmarks like rivers and highways to build their own aerial maps as they fly.

It’s yet another remarkable adaptation of life.

Of that, 99 percent is locked up in glaciers and underground aquifers. That leaves just 1 percent of Earth’s fresh water on the surface.

From all that salt water, how does this tiny fraction of surface fresh water come to be? It’s a process of natural distillation.

Heat and wind turn seawater into water vapor. In the phase change from liquid to gas, water leaves salt and all impurities behind.

In the atmosphere, water condenses on airborne particles and rains down again.

Since Earth is mostly ocean, most rain falls in the ocean. The part that falls on land flows downhill, eventually into rivers that carry it back into the sea, to become salty again.

That brief, shining moment as surface fresh water has made virtually all land-based life possible, for hundreds of millions of years.

Here’s a practical tip: If you ever find yourself in a dire situation with no fresh water, remember this distillation process.

First, never drink seawater; it’s four times saltier than blood. To neutralize it, your organs will draw water from the rest of your body, leading to rapid dehydration.

Instead, find a way to make your own cloud. Trap rising water vapor, allow it to condense on a surface, and drain it into something that you can drink from.

They returned that night to scale the museum wall, climb through a bathroom window, and steal 22 of the most precious jewels in the world.

Among them were the Eagle Diamond, the DeLong Star Ruby, and, most famous of all, the Star of India sapphire.

Sapphires are a variety of corundum, the third-hardest mineral. Pure corundum is clear, but when colored blue by titanium impurities, it’s called a sapphire. When colored red by chromium, it’s a ruby.

Mineral inclusions in a sapphire sometimes line up along its crystal lattice to reflect light in a six-pointed star.

The Star of India, besides being huge and nearly flawless, has stars that are visible from top and bottom.

The thieves didn’t go far with it, renting a luxury apartment near the museum.

An informant tipped off the police, who raided the place and captured one of them.

The other two fled to Florida; the cops pursued and, a few days later, apprehended them, too—but not before they dispersed the jewels.

The Eagle Diamond was never recovered, probably cut into several smaller stones.

The philanthropist John D. MacArthur, paid a ransom to have the DeLong Ruby returned to the museum.

One of the thieves finally led detectives to the Star of India, which they found with several smaller gems in a wet leather bag in a bus-station locker.

It’s Earth’s near-flawless creations that humans still value the most…

On the other hand, you probably know that Greenland is covered in glaciers. So why is the green one Iceland and the white one Greenland?

Legend has it that the Vikings who discovered Iceland wanted to protect it from settlement, so gave it an unflattering name.

But it was actually a matter of perspective. The first explorer to Iceland had a terrible trip. His daughter died on the long voyage. He arrived in winter and his livestock froze. That spring, his ship was nearly sunk by icebergs.

Fed up, he called it as he saw it: Iceland. And the name stuck.

A century later, another Viking explorer was visiting Iceland when he got in a fight with the settlers and was run off the island.

He sailed west and found Greenland, which was warmer than today, and the coastal areas were indeed green. Wanting to attract settlers, he called it Greenland.

They came, and built farms and grazing operations—which lasted until around 1400, when the climate cooled.

Greenland’s glaciers expanded, leaving less green land.

Today the Arctic is warming, which means Greenland’s glaciers are melting, and it may one day be greener again.

Conversely, cold glacial meltwater entering the ocean from Greenland could blunt the Gulf Stream that warms Iceland, making it icier.

Nearly all male elephants and most females have tusks. These are just elongated lateral incisors that grow outward once the elephant loses its baby teeth.

But a small percentage of elephants are born without these teeth and never develop tusks.

In 1919, the South African government brought trophy hunters to the East Cape to exterminate elephants that were eating crops and trampling farms.

By 1931, only eight females survived, and half were tuskless—perhaps because they made the least attractive trophies. Instead of natural selection, this was human selection.

Fortunately, public opinion forced a change of heart and a preserve was established to protect the elephants.

The tuskless matriarchs had tuskless offspring, and today nearly all female elephants in the park lack tusks.

A similar thing happened in Mozambique. During a 15-year civil war, soldiers poached elephants for their meat to feed the troops and for their ivory to sell to buy more weapons.

Again, elephants with tusks were killed, and by the end of the war, half the females were tuskless. As the population has rebounded, a large portion of females remain without tusks.

But with the hunting pressure off, experts think natural selection may again favor animals with tusks—and both groups may eventually become tusked again. 

They’ll probably know that fireworks originated in China. But they likely won’t know they started as simple bamboo sticks thrown into a fire.

The air inside the hollow stalks expanded, then exploded, making a “crack” that the ancient Chinese used to ward off evil spirits.

A few centuries later, legend has it that a kitchen recipe gone awry combined charcoal, saltpeter, and sulfur. Who knows what food they were trying to make…but they created gunpowder.

Warlords quickly recognized its military potential. Luckily, firecracker enthusiasts pursued its celebration potential.

They filled those same bamboo tubes with gunpowder, to make a far bigger noise, then used more gunpowder to launch ever-larger firecrackers into the air. And fireworks were born.

When Marco Polo came to China, he was so impressed that he took fireworks back to Italy, where they’ve been a hit for over 700 years.

The Italians were the first to add common minerals like gypsum and calcite to produce colored explosions.

The science has come a long way since, now blending in a variety of metal salts and exotic minerals to make better fuels and to add deeper colors and special effects.

So when you see a brilliant finale of red, white, and blue, you can shout, “Wow! Celestine, barium oxide, and copper ore!”

Then you can blame EarthDate for making you the science nerd at the party.

The answer may surprise you.

The heat of the sun can’t actually radiate through space. There would need to be particles of some element to conduct its heat; but space is a vacuum.

Instead, the sun emits electromagnetic energy: ultraviolet, visible and infrared light, X-rays, and radio waves.

When this solar radiation finally meets Earth’s surface, it warms it. And that radiates heat back upward, warming the atmosphere from the bottom up.

So is that why it’s warmer lower and cooler higher?

Not exactly. It has more to do with air pressure.

Like all gases, the air in our atmosphere is a poor conductor—because it’s not dense with particles.

However, the atmosphere does have mass. And its weight bearing down on the air at the surface compresses it more than the air at altitude.

The compressed air is denser with molecules, which are more likely to collide, and these collisions produce heat.

That means the air near the surface is not only better able to conduct Earth’s reflected heat but generates its own heat because it’s dense.

This hot air can indeed rise. But as it does, the atmospheric pressure decreases, the air expands, and it cools.

So, even though they’re closer to the sun, thin air in the mountains keeps them colder than the thicker air in the lowlands surrounding them.

That’s because pterosaurs evolved more than 80 million years before the earliest birds, with many of the same characteristics.

Pterosaurs had hollow bones, some with an even more sophisticated structure than birds; it’s one of the things that allowed them to grow to such immense size: the largest pterosaur was bigger than an F-16 fighter jet, with a wingspan of 33 ft.

These gigantic beasts were able to launch themselves because they were quadrupeds, which allowed them to run to get airborne.

Pterosaurs may also have been warm-blooded like birds, as suggested by pelts of hair-like bristles found in the fossil record.

They appear to have had similar social structures to birds: they reared young in nests, and some species appear to have traveled in flocks.

Many pterosaurs sported eye-catching crests like today’s birds. Theirs were made of bones and skin, but are thought to have served the same purpose of attracting mates.

Sharp-toothed predators, peg-toothed clam crackers, filter feeders living on lakes, pelican-like ocean fishers. Insectivores the size of today’s cardinal. Swoopers, stalkers, and scavengers.

They did it all, they did it well, and they did it first!

Why did more than 200 species of pterosaurs perish when the Chicxulub asteroid struck, allowing birds to take their place? It’s a mystery that scientists are still working to solve.

Every beach is a mystery. Read the clues right and they’ll tell you about the area’s ocean floor, sea life, and geology.

You can start with the usual suspects: waves. They make or break a beach.

Gentle slopes and slow-rolling waves produce wide beaches and shallow, sand-rich bottoms extending way off shore.

Steep slopes and tall, angular waves that crash hard rob the beach of sand, keeping it narrow and rocky.

Now scoop up some sand for a closer look.

Fine, rounded grains that look mostly alike mean the beach is made of rocks and minerals from far away, broken down over long time frames as they traveled in rivers or ocean currents.

Pebbly, angular sand grains with lots of diversity come from nearby coastal headlands or fast-moving rivers.

White sand could be quartz, or limestone from nearby cliffs, or ground-up seashells, suggesting an ocean healthy with mollusks and snails.

Pink sand could be ground-up coral, indicating offshore reefs

Black sand is made of obsidian or basalt, like on some beaches in Spain.

Green beaches mean volcanic rocks are eroding, concentrating olivine in the sand, as you can find in Hawaii.

With a keen eye, there’s a great deal to uncover on the beach. For more clues, visit EarthDate.org.

In a warming climate, the air holds more moisture. It draws more water from plants, making them drier and more combustible.

Summers become longer, which extends the fire season and gives fire-prone lands more chances to burn.

Expanding development also puts more people in fire zones. Human activity starts four out of five fires, which increases burned areas sevenfold.

Drought across the West, intensified by development and agricultural water use, makes fires more likely.

But one of the strongest contributors to fires are fires themselves.

Wildfires, it turns out, can make their own weather—which causes them to spread.

Two of California’s biggest fires last year produced devastating firestorms.

Towering flames heat the air, creating a rapidly rising updraft, which pulls air into the base of the fire, feeding it with oxygen and increasing the intensity.

These updrafts may eventually spiral into what’s called a fire whirl—essentially a tornado of flames, with winds up to 150 miles an hour.

Meanwhile, smoke fills the air with particulates, on which water vapor can condense, forming thunderheads above fires that can produce lightning and start more fires.

Scientists are now studying fire weather, and re-creating it in lab conditions, to better understand how to control wildfires once they begin.

Heavy rain brings more foliage, which the next year becomes fuel. Wet years are often followed by high-fire years.

Wildfires are a natural process, and in many ways can be beneficial: they clear out dead plant matter, control insects and plant disease, return nutrients to the soil, and make way for new growth.

It’s even thought that, in the geologic past, fires regulated Earth’s oxygen levels, to keep them in an optimum range for life.

But fires are also dangerous to humans and our property.

So what to do about that?

Forest management helps. Clearing forests and especially slopes of deadwood helps keep fires from spreading. Allowing them to burn is controversial but reduces fuel buildup.

Better fireproofing helps, too. Some embers from wildfires are very tiny—small enough to slip between roof tiles and ignite underlying wood. New codes in fire-prone areas call for fire-resistant roof decking.

Perhaps most important, we can better monitor ourselves. A new study found that 84 percent of wildfires are set by humans. Accidentally, through downed power lines or untended campfires. Or intentionally, through arson.

It may sound obvious, but to avoid becoming victims of fires, we need to become better at not setting them.

After his trip, he studied the American West—then called the Great American Desert.

Powell realized its dryness—with rainfall below 20 inches a year—made it fundamentally different than the rest of the country.

He predicted that farming and settlement methods used in the East and Midwest would fail, and proposed to Congress a much different approach: Don’t divide the West into states with straight-line borders as elsewhere; instead, follow the water.

Organize it into commonwealths by watershed, so that all water in one area was under one jurisdiction.

His proposed map looked very different, with organically shaped borders following ridgelines and drainage plains, each unit containing its own rivers and streams as water sources.

Within those watersheds, he proposed a much larger farm size, and reserved drier areas for grazing or no development at all.

Powell’s goal was to avoid water battles in the West and better manage resources. But others had different ideas, and Congress was not persuaded.

Instead, the government embarked on 100 years of building canals, reservoirs, and irrigation systems.

These were successful in populating the West much more densely than Powell proposed.

But that population now struggles with water supply, drought, and falling water tables, just as he predicted.

The magnetic field comes out of the ground at the South Magnetic Pole, flows parallel to the surface across the equator, then dives back into the ground at the North Magnetic Pole.

Many bacteria, earthworms, and blind mole rats can sense the direction of this magnetic field and orient to it. We call this compass sense.

Migrating animals like butterflies, salmon, sea turtles, and many birds have a more advanced version called signpost sense. They read the direction and inclination of the magnetic field and create mental maps of local anomalies, or “signposts” within it, to chart their paths in three dimensions over great distances.

Scientists who study magnetoreception have found that some bacteria have particles of magnetite that align north–south. Some birds have proteins in their eyes sensitive to magnetic fields.

But for the more complex signpost sense, animals must have multiple magnetic receptors sending diverse signals that converge in the brain. And we still don’t know what those are or how they work.

One reason we may not understand magnetoreception is that we simply don’t know what it feels like, so we’re not quite sure how to study it.

We’ll look at other “sixth senses” of the animal kingdom in future episodes.

At that time, Pennsylvania was the biggest oil producer, and automobiles were scarce. Then, Pattillo Higgins, a self-taught geologist from Texas, had an idea.

A low, flat hill outside his hometown was known for black tar that oozed from it. He thought the mound was a salt dome—a rising column of salt—and that oil must have migrated from deeper formations, up its sides.

Formally trained geologists chuckled, but Higgins raised enough money to start drilling. After a few dry holes, he was tapped out.

Undeterred, he brought in more investors, eventually shrinking his own share to zero—but he kept drilling.

In January 1901, his Spindletop well finally struck oil—and did it ever! The reservoir was under such pressure that it shot a geyser of oil 150 ft into the air.

For 9 days, workers struggled under a rain of a million barrels of oil, till they were finally able to cap it.

The first six Spindletop wells produced more oil than the rest of the world’s wells combined to that point in time. The Texas oil boom had begun. Supply soared and price plummeted.

Gasoline became cheap and readily available, helping launch the automobile age and personal mobility like the world had never known—that all of us in our cars still benefit from today.

There’s that bright, sweet smell on the wind before the rain comes. Then the scent of fresh earth and grass as the rain falls. And a damp, musty aroma like a forest floor that lingers afterward.

What gives rain these distinctive aromas? And why do we find them so memorable?

Well, the pre-rain smell is ozone. Lightning in the clouds splits nitrogen and oxygen gas into single atoms, which recombine into things like nitric acid and ozone.

Downdrafts and the first drops of rain carry ozone to the ground, where we experience it as a sweet, lightly acidic smell.

As the rain starts falling, drops of water strike plants and the ground and liberate organic compounds and aromatic oils, splashing them into the air as aerosols.

Once the soil and dead leaves on its surface become wet, bacteria begin to produce geosmin, an alcohol that’s the signature musty-basement smell of decaying plant matter.

Humans are incredibly sensitive to the smell of geosmin; we’re able to pick up just a few parts per trillion in the air.

And scientists think there’s a very good reason for this. Early humans depended on natural water sources. Those who could find water with their noses prospered. Those who couldn’t may not have survived to pass on their genes, and noses, to the next generation.

The USDA map of plant hardiness divides North America into 13 zones.

Zone 1 is farthest north, with winters colder than 50 below zero. Zone 13 is farthest south, with winters around 60 degrees Fahrenheit.

Over the last 30 years, all zones have shifted a half zone to the north, as average winter temperatures increased across the Lower 48.

Models predict that plant zones will continue to move north, about 13 miles a year. And it’s happening all over the world. In Australia, the wheat belt is moving 16 miles a year.

In response, farmers in many countries have had to change the times of year they plant or harvest. Some now have a second growing season.

Warmer weather and longer seasons have allowed some farmers to grow more lucrative crops, in higher quantities—while others have seen traditional crops fail and prized land lose its value.

Where might they go for new opportunities?

As northern latitudes get warmer, lands that were once too cold to farm may become plantable. In fact, Canada is preparing for millions of acres in its northern prairies to replace farmland potentially lost in the south.

The warming climate will continue to change plant distribution and farming practices—with both positive and negative effects on global agriculture and food supply.

They’ve found that as annual temperatures climb, many species have climbed, too. On average, for every one-degree-Celsius increase, mountain-dwelling species shifted 100 meters upslope.

Because the mountains narrow as they go up, this means a shrinking habitat for those species, and often a dramatic drop in population.

For instance, butterflies in the French Pyrenees and gophers in Nevada’s Ruby Mountains have lost 70 to 80 percent of their range, as suitable habitat shifted up the slope.

Birds on one mountain in the Peruvian Andes moved 250 meters up over the past 30 years in response to a change of just one degree.

Some of the migrating species are soil microbes, which, as they move upslope, may allow tree species to move up with them. In these cases, the treeline could rise, supporting forest species on their upward climbs.

But as the climate continues to warm, earthbound species like trees, crawling insects, and mammals will eventually run out of mountain. If they can’t adapt to the warmer temperatures, they may die out.

Birds and flying insects would be able to fly to higher ridges and mountaintops—as long as there are higher ones in the region.

Regardless of cause, these are effects we can measure and observe today: plants and animals the world over are migrating to adjust to a warming climate.

They soon discovered that some elements, when heated, produce a signature light color. Hydrogen, for instance, makes orange.

When they pointed the spectroscope at the sun, they saw lots of orange—and some yellow, which didn’t match any element on Earth.

They named this alien element helium, after the Greek sun god Helios.

For decades, many doubted its existence. Until a scientist aimed the spectroscope at lava and saw the yellow again. Helium had been found on Earth.

Further study revealed that helium was being produced by the decay of uranium and trapped underground in reservoirs. It also revealed that it’s a very special element.

Helium is so light that Earth’s gravity can’t hold it. When released at the surface, it rises through the atmosphere into space.

It’s also inert: helium won’t bond with other elements, meaning it’s nontoxic and nonflammable. That makes it useful to create sterile, nonoxidizing environments for medical procedures, clean rooms, and welding. 

Helium also enters its liquid state colder than any other element. Liquid helium is therefore used to cool superconductor magnets, and in MRI machines and nuclear colliders.

So next time you see helium balloons at a party, or inhale it to sing happy birthday in a chipmunk voice, remember that helium itself is an element worth celebrating. 

And surprisingly, this closer look came in Greenland. The ice there has recorded 130,000 years of history, as the atmospheric particles of each year are deposited in a layer of ice, one atop the other.

By drilling ice cores, then analyzing these layers with microscopes and spectrometers, we can read them like tree rings to build a detailed picture of the atmosphere over time.

This has helped today’s scientists study ancient climate, volcanic eruptions, and the success or failure of agriculture as told by pollen grains. It’s also revealed a lot about Rome.

The coin of the realm was the denarius, made of silver smelted from galena, a lead ore.

When the Roman economy was booming, smelters across the Empire pumped out silver, and spewed lead fumes into the atmosphere—which wafted across Europe to Greenland, where they settled on the ice and were preserved.

When the economy slumped, the smelters went quiet, and lead-laden emissions declined.

Researchers have now analyzed the lead levels, and they closely correspond to Rome’s official history—falling during wars and in times of plague, rising after wars and in times of peace.

Rome’s imperial storytellers largely agree with the ice cores, an admirable truth in journalism that spanned 600 years.

For a one-armed geologist named John Wesley Powell, that was too much intrigue to ignore.

So in 1869, he led a team in four wooden boats on an expedition down the Green and Colorado Rivers, destined for what the Spanish called El Gran Cañon.

Within 2 weeks, a rocky rapid had destroyed one of their boats.

Within 2 months, most of their supplies were lost. Fortunately, the lightened boats rode higher in the dangerous waters.

Once in the canyon, the rapids echoed in a deafening roar. At times, the men climbed the walls to sleep in the relative safety of rock ledges.

At one point, the party was unable to portage their boats around a seemingly impossible stretch of rapids.

Three men refused to go further and tried to climb out of the canyon, while Powell and the others took two boats and pressed on.

Powell’s group made it through alive and signaled for the others to take the last boat—but the three men were never heard from again.

After 99 days, Powell and his remaining team reached their destination, but he had lost many of his records from the trip.

Unsatisfied, he returned 2 years later to do it again!

These remarkable journeys, as bold as Lewis and Clark’s Discovery Expedition, launched a movement to declare the Grand Canyon a national park.

When they looked at the photos, they saw mysterious stripes of clouds crossing the oceans.

On closer inspection, they realized these cloud trails followed the shipping lanes.

In the mid-nineteenth century, after collisions between ships, nations designated lanes across the seas that ships would follow to avoid accidents.

As traffic grew over the twentieth century, more and more ships plied these maritime highways. But what caused the clouds?

Scientists realized that the exhaust plumes of hundreds or thousands of diesel-fired ships carried streams of aerosols and fine particulates into the low atmosphere, along the shipping lanes.

Water vapor condensed on these to form the trails: the ships were making their own clouds.

Newer satellites discovered something more. They picked up magnetic pulses from lightning patterns across the ocean, and the lightning also followed the shipping lanes.

Scientists now understand that the tiny water droplets in the ships’ cloud trails, finer than in regular clouds, are more conducive to lightning formation.

The ships actually make their own lightning storms, and the weather in their wake is more severe than over open ocean.

So if you’re having one of those days when it feels like a storm cloud is following you around—if you’re the captain of a cargo ship, it just may be.

Today, scientists are working to put CO2 from fossil-fuel combustion and agriculture back into the ground rather than into the atmosphere—by mimicking Earth’s natural carbon cycle.

Capturing and compressing CO2 from the exhaust stream of, say, a coal power plant, is challenging and expensive. But when done, the gas becomes a low-density liquid.

Researchers have developed and tested methods to pump it deep underground—into depleted oil fields, coal seams, and rock formations whose small pores are filled with saltwater. 

Once there, it dissolves and the saltwater becomes carbonated, less than a soft drink. Studies suggest that carbon can remain trapped in these formations indefinitely, similar to the way hydrocarbons are trapped.

While international tests of these processes have been successful, other more experimental methods are striving to turn CO2 gas into useful solid materials.

New trials have injected CO2 into volcanic basalt, where it formed carbonate minerals.

Others combine carbon and calcium, similar to the way snails and clams draw them from seawater to make their shells.

The challenges with all these methods are expense and scale. Storing enough human-produced carbon to make a difference on the climate, in the time frame needed, will not be easy.

But thanks to government and industry investment in research, we now have enough experience to begin large-scale tests.

Given these remarkable properties, scientists have studied it closely.

Spiders make silk with their spinnerets, tiny organs beneath their abdomens.

Before it’s spun, the silk is a gel of liquid proteins. The spinnerets remove water from the gel and extrude it through an acid bath, aligning the proteins into a solid fiber.

Each spinneret has multiple spigots. And each of those makes a single filament that the spider combines to create different silks: fine or coarse, sticky or not.

Scientists haven’t been able to re-create spider silk chemically, so they’ve enlisted another silk-spinning creature to help: the silkworm.

While spiders are almost impossible to domesticate, the silkworm has thrived in captivity for centuries. Its silk is beautiful but comparatively weak.

So scientists turned the worms into real-life Peter Parkers, giving them genes from the spider.

These genetically modified silkworms spin their cocoons as always, from a single kilometer-long strand—but this time of spider silk.

Other scientists have developed genetically modified bacteria that organize proteins similar to how spider spinnerets work.

With these developments, we may soon have fabric and other materials with the amazing properties of spider silk.

In the first years after impact, dust and aerosols blocked the sun’s light and heat, which slowed photosynthesis.

Plants died, along with most things that depended on them, as the food web collapsed.

Most types of plankton in surface ocean waters also died, and rained down through the water column, where bottom-dwelling scavenger species had a field day.

Large organisms with fast metabolisms and higher food needs starved, while some species of less than 50 lbs with slower metabolisms hung tough.

Specialized species suffered worst. Generalists that could more easily adapt fared better.

Early mammals and birds—avian dinosaurs—quickly began to fill the environmental niches left empty by extinct larger species.

Within 300,000 years, a blink of an eye in evolutionary terms, there were productive ecosystems across Earth.

Strangely, one of the places productivity recovered fastest was within the asteroid crater. Scientists are studying why.

It would be another 10 million years before evolution filled all empty environmental niches and the diversity of life equaled what it was before the impact.

The resulting mix looked very different than before and allowed the rise of mammals and birds and, eventually, humans.

From the point of impact, a blast wave of heat rushed outward at nearly the speed of light, followed by scorching winds that reached 500 miles an hour.

These were followed by a massive earthquake felt around the world that may have caused landslides across the planet.

Shortly after came tsunami waves up to 1,000 ft high, racing across the Gulf of Mexico and traveling many miles inland, up the Mississippi River, covering Caribbean islands and swamping Atlantic coastlines.

Debris from the impact rained across the region, forming deposits up to 1,000 ft thick. The debris was hot enough to ignite massive wildfires across North America that may have burned for months. 

And the long-term effects were even worse! 

Ash and dust blocked out sunlight, while billions of tons of vaporized rock formed aerosols that blocked the sun’s heat.

In this cold twilight, the surface temperature of Earth fell as much as 40 degrees Fahrenheit and stayed that way for 15 to 20 years.

Mere decades later, once the aerosols settled out, greenhouse gases from the wildfires helped to warm the atmosphere more than 10 degrees higher than pre-impact.

It’s amazing that anything survived this destruction!

But it actually paved the way for… you and me, which we’ll talk about on another EarthDate.

Remarkably, one of the biggest drivers of mineral evolution… is life.

A mineral is simply an element or elements on the periodic table, arranged in a certain crystal structure. For instance, the hardest mineral, diamond, is formed of the element carbon.

One of the softest, graphite, is also formed of pure carbon, but it’s a different mineral because it has a different crystal structure.

When Earth formed, over 4.5 billion years ago, there were just 12 minerals, including diamond and graphite.

Over the next 2 billion years, plate tectonics began to act on mineral evolution.

Earth’s crust was subducted into the mantle, melted, remixed, and recycled, and the number of mineral species gradually increased to 1,500. And there it stopped…

Until life developed.

Early algae and phytoplankton converted huge volumes of carbon dioxide into oxygen.

This new oxygen-rich environment produced more than 2,500 new oxide and hydroxide mineral species.

Microbes then began to transform minerals chemically, and this added another 500 mineral species.

Multicell organisms evolved and interacted with existing minerals to build their exoskeletons, shells, bones, and teeth, in the process creating hundreds more mineral species.

Because Earth has plate tectonics and life, it now has over 5,000 minerals—10 times more than any other planet in the solar system.

The Bajau are sea nomads in Indonesia, the Philippines, and Malaysia, who live on boats and follow fish populations.

Traditionally, they come ashore only to trade their catch and escape storms.

To make their living diving for fish, the Bajau have adapted to do things the rest of us can’t. In fact, they’ve developed some of the same capabilities as seals and whales.

When they dive, their bodies direct blood away from their extremities and toward their brain and organs.

Most importantly, they’ve developed 50 percent larger spleens, which act like an oxygen reserve, storing and then releasing more red blood cells into their systems when they dive.

All Bajau, even those who don’t dive, have an enlarged spleen, indicating it’s genetic.

With these adaptations, most Bajau can spend 5 hours a day underwater. They dive easily to 60 ft and stay there for minutes at a time!

They can go to depths over 200 ft with nothing more than wooden goggles and weight belts to pull them to the bottom. Then surface and do it again.

Western scientists are studying the Bajau to see how they can thrive with less oxygen—a condition called hypoxia, which can cause free divers to lose consciousness and drown.

Perhaps the secrets of the Bajau will save lives elsewhere.

But the Gulf Stream is just one part of the global ocean conveyor, a system of currents that connects the world’s oceans.

In tropical seas, wind and tides drive warm surface currents, like the Gulf Stream.

Near the poles, cold air, evaporation, and ice formation make the seawater colder and saltier. It sinks to the bottom, and warm tropical water is pulled up to take its place.

In this way, the global ocean conveyor carries tropical heat toward the poles. And carries nutrient- and carbon-rich water from the poles to the tropics, where it feeds phytoplankton, the base of the world’s food web.

The conveyor’s stability over more than 10,000 years has helped regulate climate, weather, and fish populations, contributing to the rise of human civilization.

But since 1850, before the Industrial Age, the Gulf Stream has shown signs of slowing. It’s at its weakest in 1,000 years.

In 2009 and ’10, it moved a third less warm water than usual, causing colder winters in the Eastern U.S. and Europe.

Melting ice in the Arctic has been releasing freshwater onto the ocean surface, disrupting the flow of the cold, salty waters that drive the North Atlantic part of the ocean conveyor.

In this way, paradoxically, a warming climate can bring colder winters in the north.

Greece and Turkey lie along massive fault zones. Faults, when they move, create earthquakes. Spring water tends to follow these fault systems, and the Greeks, following the water, did, too.

Fault lines also create cliffs, which provided natural defenses for the cities. And fault zones tend to form surface depressions where soils can accumulate, making them good for agriculture.

So the faults gave Greek cities water, protection, and fertile soil—but it gave them something else, too.

Many of the fresh-water springs were heated along fault zones.

The Greeks built baths and temples at these hot springs, some of which emitted gases that could induce human trances.

At the famous Temple of Apollo at Delphi, traces of ethylene, which produces a state of euphoria, have been found. These fumes were known as the “Breath of Apollo” and may have helped the priestess communicate with the gods. 

Other cities and sanctuaries were built along faults that the Greeks believed were entrances to the underworld.

When an earthquake toppled their structures, they usually rebuilt in the same spot…unless the quake also cut off the water supply.

Earthquakes in the time of the ancient Greeks were considered mystical events. And before multistory buildings, the risks of living on fault lines were offset by the many benefits.

Here’s why: the iron it’s made of came from the heart of a distant star.

Stars begin their lives as giant balls of gas, mostly hydrogen, the first element on the periodic table, with one proton.

Under the force of the proto-star’s enormous gravity, hydrogen atoms fuse together to produce helium, with two protons.

This nuclear fusion releases a huge surge of energy, and the star is born.

Hydrogen continues to fuse into helium, releasing more and more energy.

Helium atoms then fuse into carbon atoms, which fuse into silicon atoms, with each subsequent element being heavier.

All this nuclear fusion releases more energy than it takes to fuse the atoms together. And so, the process continues, for millions of years…until the elements fuse into iron.

At that point, it would take more energy to fuse iron into something else than the resulting reaction would produce.

So fusion stops, and the star begins to die.

Soon, the gravity of its iron core becomes so strong that the star collapses on itself, then explodes outward in a supernova, scattering iron across the universe…which eventually forms planets like ours. And our cars.

Specifically, they exchange sugars, and chemical and electrical signals, with each other.

The largest trees are now known to “mother” the surrounding forest. They give their sugars back to the entire soil community, to support neighboring plants and trees.

They’ve even been shown to preferentially identify young trees within their own species, and send them a larger serving of sugars via the fungal network.

And, plants and trees have learned to communicate through the air.

Many studies have shown that, when attacked by insects or disease, they release distress hormones to other plants, as well as defensive compounds.

Pine trees, for instance, when preyed on by caterpillars, send out pheromones that attract wasps to the forest, which prey on the caterpillars.

Acacia trees, when eaten by grazing giraffes, release ethylene gas, which prompts other acacias to flood their leaves with bitter tannins. Giraffes have learned to graze downwind...

Traditional lumber practices have removed large trees, with the idea that it allows other trees to access their sunlight. This new research may require rethinking how we maintain healthy forests.

This isn’t to say that trees can think—at least not in the way that humans define sentience.

But they certainly have a type of language that has allowed them to thrive for millions of years. We’re only now learning to understand it.

He was right 500 years ago, and he’s still right today.

That’s partly because the study of space is mysterious and cool, and there really wasn’t much interest in studying dirt. Until recently...

We now know that about 90 percent of all land-based species live in the soil, not on it. Most of these are microscopic, but they’re incredibly plentiful: there are more microbes in a handful of dirt than people on the planet.

And they’re also incredibly important: without soil microbes, plants might not exist.

Plants require nitrogen and other trace elements, and it’s soil bacteria, and the single-celled organisms that eat them, that process these elements into forms that the plants can use.

With this knowledge, agricultural researchers are reintroducing bacteria into depleted soils to increase the health and nutrition of crops.

Most plants also depend on soil fungi, and this relationship is symbiotic.

The fungi penetrate or encase the roots of plants to draw out what they can’t make themselves: sugars from photosynthesis.

In exchange, the fungus filaments stretch deep into the soil, gathering water and nutrients from a volume 100 times greater than the roots could reach on their own.

This fungal network can even join plants together beneath the soil, which allows amazing things to happen—and we’ll talk more about that on another EarthDate.

To understand this strange connection, we need to know a bit about Earth’s atmosphere.

The lowest part, the troposphere, extends from the surface up 4 to 12 miles. It’s where Earth’s weather happens.

The stratosphere, above that, is dry and less active.

Dust and ash particles carried into the troposphere by volcanoes, fires, or other sources will quickly fall or be rained out.

But when a large volcano erupts, it blasts ash and gas through the troposphere into the stratosphere.

There, sulfur gas forms microscopic droplets of sulfuric acid. These “sulfate aerosols” can remain suspended for years.

One way scientists measure them is by looking at lunar eclipses. If they’re murky and dim, the stratosphere is clouded with aerosols. If they’re bright and defined, the stratosphere is clear.

Large volcanoes in the past have put up enough aerosols to reflect the sun’s heat and cool the surface of Earth by as much as 1°F.

But in the last two decades, the stratosphere has been remarkably clear, which has allowed more solar energy to reach Earth.

Some scientists estimate this has caused half the global temperature increase seen during this period.

Another example of how Earth’s processes are linked in surprising and complex ways.

The winter solstice comes on or around December 21st—and 6 months later in the Southern Hemisphere. Leading up to it, the days appear to be dying.

The dawn comes later, the sunset earlier. Nights get longer and colder. In far northern and southern latitudes, this is very keenly felt.

Then on the solstice, things turn around. The day after is a little longer, and they keep getting lighter and brighter.

So the solstice has always been associated with rebirth—of the sun and of a new year.

Asian, Middle Eastern, North and South American cultures all had, and still have, festivals marking the rebirth of the sun.

The Romans, too, celebrated Saturnalia, dedicated to the sun god Saturn, characterized by charity and gift-giving.

In the 4th century when they converted to Christianity, they turned their festival of the sun’s rebirth into a celebration of a different son’s birth. This gave us Christmas, on December 25.

Later, when the Vikings became Christians, they brought Nordic solstice traditions: evergreen trees, holly, and mistletoe, all symbols of life in the dark winter.

So this holiday season, you might consider a solstice party.

It’s the astronomically correct way to ring out the old year and welcome the birth of the new.

We do that mostly by burning a resource like coal or natural gas to boil water, which makes steam, which turns a turbine, connected to a generator.

Heat from a nuclear reaction or a geothermal well are other ways to make steam and turn a generator.

Water held behind a dam, then released to flow through turbines, turns generators without having to produce steam.

All these generation systems produce emissions—like water vapor, CO2 or other gases, particulates, or a small amount of nuclear waste.

And all of them are available on demand, which is very important, because we can’t store electricity very well at scale. So it must be made when we need it.

Wind, too, turns a generator. It makes up about 1 percent of global power generation.

Solar, the only one to produce electricity without a generator, makes up another 1 percent.

Wind and solar produce no emissions. But they have other environmental impacts, in mining materials, manufacturing, the large amounts of land they occupy, and eventual disposal.

And because they make electricity only when the sun shines or the wind blows, we have to back them up with other power sources.

The modern world depends on our electricity system, and it’s something we’ll talk more about.

Dressed in leather and fur, he was mid-40s and extremely fit. He carried a wooden bow, flint-tipped arrows, and a copper axe.

He had no way of knowing that in an hour he’d be dead.

5,300 years later, some hikers discovered his body, melting out of a glacier.

Local police called in forensic experts, and so began a 30-year investigation into the best-preserved mummy from pre-modern history.

They traced the minerals in his teeth to a nearby groundwater source, to determine where he lived.

They looked at food and pollen in his gut to re-create his last day of meals and where he ate them.

Ötzi the Iceman, as they called him, had walked from his mountain home to the valley floor. That night, judging from a telltale slash on his hand, he got into a knife fight.

The wound had begun to heal by the time he died, suggesting he won it.

What had not healed were a fatal arrow wound to his back and a cracked skull. Someone had tracked him into the mountains and ambushed him.

His valuable copper axe was not taken, suggesting a revenge killing. Perhaps the killers buried him in snow, beginning his mummification.

Today, Ötzi rests in a museum freezer near where he was discovered. A model of him in life stands in the same building, while 3D printings of his body are studied around the world.

But half a million years ago, the English Channel didn’t exist: Britain was attached to Europe.

At that time, Earth alternated between glacial and interglacial periods, as it still does today.

During glacial periods, some of Earth’s water is held in vast glaciers, on top of continents rather than in oceans, which causes ocean levels to drop hundreds of feet.

Toward the end of one of these glacials, as the ice sheets started to melt, an enormous lake formed in the North Sea—dammed in the north by a massive wall of ice and in the south by a rock land bridge.

Eventually water levels rose so high that the lake began pouring over the British land bridge in gargantuan waterfalls.

Engineers planning the path of the Chunnel discovered this. Using seismic studies, they found huge, deep pits in the seafloor filled with rubble and sediment, and designed the Chunnel to avoid them.

Eventually scientists collected enough data to recognize the pits as plunge pools that those giant waterfalls would have made from millions of tons of water, pounding down on the seafloor over centuries.

The waterfalls began to erode the land bridge, but it held—until, a couple of glacial and interglacial cycles later, another flood finished the job.

The channel formed—causing a natural Brexit thousands of years ago.

Both are soft, heavy metals. If they could make the dull one into the shiny one, they’d be rich. Right?

Maybe not.

Thousands of years before them, another metal, iron, was eight times more valuable than gold. It could only be found in its pure metal form in iron meteorites. Assyrians and Egyptians made prized iron jewelry, which we find in ancient tombs.

Then some alchemist of their time figured out how to smelt iron from common iron ore, like hematite and magnetite.

When supply boomed, the price plummeted. Iron eventually became the least expensive metal on Earth.

That’s because iron, as found in ores, is our most plentiful element by mass.

Iron makes up most of Earth’s core, which produces Earth’s magnetic field, protecting us from cosmic rays and solar wind.

Iron is the main ingredient in steel, an alloy of iron and carbon. We make a billion tons a year, and use it in everything, especially large buildings—which might be impossible without steel.

Iron is also abundant in the human body; it carries oxygen in the blood and gives blood its signature color…along with many other red things on Earth, from rocks and soil to farmers’ barns, painted with iron oxide pigments.

Iron is common and cheap and incredibly useful, so in some ways, that still makes it a lot more valuable than gold.

But what exactly happened when a rock twice the size of Manhattan smashed into our planet— with the force of 10 billion atomic bombs?

It punched a hole in Earth’s crust 50 miles wide and 20 miles deep, causing nearly a million cubic miles of solid rock to behave like liquid.

Like when a rock lands in a pond, the sides of the crater splashed outward, up, then collapsed. The center of the crater rebounded, rocketing up higher than Mount Everest; then it, too, collapsed.

Earth’s crust rippled like the surface of water. A ring of ridges spread out from the impact site.

This giant “splash” on Earth’s surface happened in a matter of minutes. Then, the rocks froze into their new positions and were protected from erosion by layers of marine sediment.

A 2016 mission drilled into the ridges circling the crater floor. The explorers found large sections of melted rock.

Below that, they found granites so badly pulverized that they were less dense than normal granite.

And, as often happens in science, one insight leads to another. 

A recent space mission had discovered that the moon’s crust is less dense than it should be, and scientists wondered why.

The crater on Earth suggests it’s due to 4 billion of years of impacts on the moon’s famously cratered surface.

But what exactly happened when a rock twice the size of Manhattan smashed into our planet— with the force of 10 billion atomic bombs?

It punched a hole in Earth’s crust 50 miles wide and 20 miles deep, causing nearly a million cubic miles of solid rock to behave like liquid.

Like when a rock lands in a pond, the sides of the crater splashed outward, up, then collapsed. The center of the crater rebounded, rocketing up higher than Mount Everest; then it, too, collapsed.

Earth’s crust rippled like the surface of water. A ring of ridges spread out from the impact site.

This giant “splash” on Earth’s surface happened in a matter of minutes. Then, the rocks froze into their new positions and were protected from erosion by layers of marine sediment.

A 2016 mission drilled into the ridges circling the crater floor. The explorers found large sections of melted rock.

Below that, they found granites so badly pulverized that they were less dense than normal granite.

And, as often happens in science, one insight leads to another. 

A recent space mission had discovered that the moon’s crust is less dense than it should be, and scientists wondered why.

The crater on Earth suggests it’s due to 4 billion of years of impacts on the moon’s famously cratered surface.

Then, in the 1970’s, geologist Walter Alvarez and his physicist father Luis found a layer of unusual clay corresponding to the time of the extinction.

They discovered it contained a high concentration of iridium, a metal that’s very rare on Earth: it comes only from meteorites.

This intrigued other scientists, who looked at rocks from the same geologic horizon in different locations—and found more iridium. They began to suspect that a massive impact may have caused the mass extinction.

In the Caribbean, the clay layer was far thicker. If an event had happened, it must have been nearby.

Decades earlier, the Mexican state oil company had drilled exploratory wells on the Yucatan peninsula, west of Cancun. Rather than oil, they believed they’d hit a buried volcano.

So the scientists reexamined those samples and found the rocks weren’t volcanic after all, but showed signs of a profound impact.

They turned to modern aerial surveys and satellite images, which revealed an enormous circular feature with sinkholes lining its rim.

And they knew they had found it! Directly across the Gulf of Mexico from New Orleans was an ancient impact crater 125 miles in diameter.

This was where an asteroid struck Earth, ending the rule of the dinosaurs.

Jet streams are rivers of wind, 5 to 9 miles up, in the high atmosphere. They’re caused by solar radiation heating rising air, which is then deflected sideways by Earth’s rotation.

They can move up to 275 miles an hour and are strong enough to push weather around and carry moisture, dust, or volcanic ash across oceans.

There are four jet streams on Earth: a polar and subtropical jet in both the Northern and Southern Hemispheres. And their paths can fluctuate. 

When they drift toward the pole, they pull warmer air with them, causing hot summers and droughts in the middle of continents and rain in the subtropics.

When they drift toward the equator, they pull cold air from the pole, causing harsher winters in the midcontinent.

Scientists in Europe studied tree rings in the UK and the Mediterranean to analyze patterns of temperature and rain.

They found that, since 1960, the northern polar jet had drifted more frequently than in any period in the last 300 years, bringing droughts to the south and floods to the west in some years, and the opposite the next.

Climatologists theorize that a generally warming planet may be influencing the path of the jet stream. But most scientists agree that we really don’t know the cause.

It’s one more of those big mysteries blowing around, right here on Earth.

When humans arrived in Europe, they were at the top of the food chain, along with Neanderthals, big cats, bears—and wolves.

Archaeological records suggest that humans soon began to domesticate wolves, which quickly evolved into proto-dogs, and joined the hunt.

The dogs did what they did best—chasing large prey over distance, tiring and cornering them. Man stepped in with spears and arrows to close the deal, sparing dogs the dangerous part of the kill. Then they shared the meat.

Butchering sites for large animals like mammoth would have attracted other carnivores. Scientists believe early dogs also helped keep scavengers away.

Fossilized remains show early dogs were similar to huskies, but bigger. The skeletons show healed broken bones, suggesting a rough hunting life but also care afterward.

By contrast, Neanderthal sites show no evidence of a partnership with dogs.

Humans and dogs became such a dominant hunting force, researchers believe, that they simultaneously eliminated large prey and outcompeted not just Neanderthals but most other large predators.

So the next time you see a dog, give ‘em a big “thank you” belly rub.

They were essential to human success. And with that, they guaranteed their own—and a friendship lasting 50,000 years.

Then in August, the top of that mountain exploded 10 miles into the atmosphere! Ash and stone rained down on Pompeii for a day. Most residents fled.

The 2,000 who stayed thought they had escaped the worst of it—then a cloud of hot gas rolled down the mountain, suffocating them. Their bodies were encased in ash, to be found almost 2,000 years later.

There are two main types of lava, and Vesuvius has the more dangerous kind. It’s high in silica, making it very viscous, or thick, so that it traps the gases that were responsible both for the mountain’s explosion and its deadly clouds.

Conversely, Hawaii’s Kilauea has been continuously erupting since 1983. Its lava is high in iron and magnesium, flows easily, and therefore traps less gas, making it much less explosive. Scientists can walk right up to it and sample lava.

Since 79 AD, Vesuvius has erupted 30 more times. It remains the only active volcano in Europe.

Scientists know that it will erupt again but can’t be sure when or how dramatic it will be.

Some expect soon, and they’re keeping a close eye on this lightly sleeping giant.

It might surprise you to know there are also many places where we’re putting water back.

This aquifer management takes many forms.

Perhaps the simplest is called conjunctive use. That means providing surface water, during wet times, to users who would normally pump groundwater.

Another method is called managed aquifer recharge. It routes surface water into man-made or natural infiltration basins, where it can gradually seep into the aquifer.

Perhaps the best example of this channels floodwater away from population areas and into recharge ponds.

Surface infiltration has the added benefit of purifying the water as it percolates through layers of soil and rock.

In the most elaborate method, called aquifer storage and recovery, water is pumped directly into aquifers to stabilize or reverse groundwater depletion.

It has been used in coastal areas to stop saltwater from gradually entering aquifers and replacing freshwater.

Long-term studies show these practices are working. In California, water tables would have dropped hundreds of feet deeper without aquifer management. In parts of Arizona, they’re actually rising.

This doesn’t mean we can get cavalier about freshwater use. But it does show how human ingenuity can address critical environmental problems.

On the bottom, there’s a thick plastic membrane and a layer of compacted clay, to keep liquids from entering the groundwater.

Above that, the fill area is divided into cells for each day’s garbage. As trucks dump garbage into the cell, it’s compacted to become as small as possible.

At the end of the day, the cell is closed off with a layer of soil, and perhaps another layer of plastic, making it water- and airtight.

Most garbage won’t break down in this environment, though anaerobic bacteria will digest food and organic waste and produce methane, also known as natural gas, the same kind you burn in your stove.

Because it’s flammable, the methane has to be flared off. Or it can be collected and sold for industrial use. Or used to run electric generators at the landfill.

America leads the world, by a wide margin, in garbage production, with more than 1400 lbs per person per year. More than half of it ends up in landfills.

And 65 percent of that is packaging: cardboard, paper, plastic, bottles, and cans—nearly all of which could have been recycled.

On average, recycling costs about half as much as storing garbage in a landfill. So if you’d like to reduce your garbage footprint and your city’s municipal waste cost, recycling is the way to go.

Then, around 315 million years ago, they were the first creatures to learn to fly.

Insect wings are actually the most durable part of their body, and the most likely to appear in the fossil record, giving us a pretty good idea of insect development.

Their size increased in direct relation to the amount of oxygen in the atmosphere. Once oxygen hit 30 percent—9 percent higher than today—the largest insects had wingspans over 2 ft!

Around the same time, avian dinosaurs developed, and large insects were easy prey—to survive, they became smaller, faster, and more agile.

Dragonflies developed speed; they’re able to hit 35 miles an hour but have the most primitive kind of wing.

Flies developed maneuverability; their shorter, folding wings allow them to dart into small openings.

Other insects evolved new uses for wings. The front wings of beetles became hard covers, to protect them from predators or while burrowing.

The wings of some moths became camouflage, to blend into specific environments. Butterflies developed brightly colored wings to attract mates or to warn enemies they’re poisonous.

Grasshoppers and crickets can even use their wings to fill the air with sound.

We tend to take winged insects for granted or consider them a nuisance. But next time you see a dragonfly hunting mosquitoes or hear a cicada sing, you’re witnessing evolutionary biology hundreds of millions of years old.

Farmers developed an irrigation system that trapped floodwaters in their fields using dams. They let the water recharge the soil for a few months while the organics settled out, providing nutrients to the earth.

They’d then release the water to the receding river and plant their crops. In this way, year after year, the fields could produce enough food to sustain a large population living in the desert.

The floods were the direct result of African monsoons, which fell on the highlands of Ethiopia, the headwaters of the Nile. If the rain didn’t fall, the Nile wouldn’t flood. And there were some years that it didn’t.

Volcanic activity in the region filled the atmosphere with ash and gas, reflecting the sun’s heat, reducing evaporation and, therefore, rainfall.

Geologic and historical records now allow us to closely correlate volcanic eruptions with reduced Nile flooding, reduced crop production, reduced tax revenue for the state, and higher incidence of famine and revolt from the populace.

Especially high volcanic activity in the last 300 years of the Egyptian Kingdom contributed to its eventual fall to the Romans.

Yet another example of how connected human civilization has been, and continues to be, to freshwater supply, weather patterns, and the geology of Earth.

But it had otherworldly connections centuries before that.

Many Plains Indian tribes gave the tower mystical significance. Most of their stories revolve around children being chased by a giant bear.

They climb atop a rock, and to save the children, the gods make the rock rise from the prairie. The angry bear scratches its claws on the tower, creating its signature fluted sides.

This legend gave rise to the Crow, Arapahoe, and Cheyenne name for the tower: Bear Lodge.

Geologists tell a different story:

The tower began as a shaft of hot magma that formed in sedimentary layers near the surface. The magma slowly cooled underground around 40 million years ago, forming the columns on its outer surface. Eventually the sediments around it eroded away, exposing the tower, which rises more than 800 ft above the plains!

Today, the tower’s long cracks and columns make it one of the world’s foremost rock-climbing sites—except during the month of June, when climbers respect Native American traditions and leave the tower to their ceremonies.

One October long ago, I tried climbing it myself. We got within a hundred feet of the top before snow turned us back. Perhaps the sacred bear didn’t want us in his lodge that day.

Their ancestors climbed out of the ocean 360 million years ago, developed lungs and legs, and evolved into mammals. Then, 50 million years ago, they walked back into the sea.

To survive there, they developed specialized behaviors, which require even more special biology.

Perhaps most famous is echolocation. They move air between sinus cavities to emit sound. When it bounces back to them, they don’t hear it with their ears, but feel it in a fatty fluid in their lower jaw.

Only toothed whales, like sperm whales, orcas, and dolphins, can echolocate—a skill we think they developed to hunt prey, especially squid, in the darkness of the deep ocean.

Baleen whales focused on other prey, floating shrimplike creatures, and for this they developed comblike plates in place of teeth.

They can’t echolocate but are known for their elaborate songs. We think they use these for communication. But we’re not sure how they produce them, since they don’t have vocal chords.

Both types of whales can hold their breath for 45 minutes or longer. To do this, they reduce their heart rate and cut blood flow to some organs, like the stomach, while providing it to others, like the brain.

Even their blood is specialized. It can carry far more oxygen than land-dwelling mammals, and they have much more of it.

Whales are an amazing example of what evolution can do, given enough time.

Why does Earth alternate between these extremes? Research points to plate tectonics and volcanic activity.

Plate movement causes continents to be pulled apart and pushed together, with varying amounts of volcanic activity.

When there’s lots of activity, volcanoes emit huge volumes of CO2 and methane into the atmosphere, which can trap enough heat to bring about a Greenhouse period.

Conversely, when volcanic activity decreases, CO2 and methane decrease, and the Earth can cool.

Continental movement also affects ocean circulation. If Earth’s poles become isolated from the warm waters near the equator, they can freeze more easily.

And plate movement can bury large volumes of organic carbon in sediment layers, stopping it from reentering the atmosphere.

Within Icehouse periods, there are shorter glacial cycles, interrupted by milder interglacials, like the one we’re in today. Earth alternates between more ice and less ice mostly because of changes in its orbital path.

When Earth’s orbit stretches farther from the sun, Earth cools and continental glaciers form. When it moves back closer to the sun, the ice melts.

Understanding the causes of these long-term and short-term climate cycles helps us to better understand the complexities of Earth’s climate today.

Hotter periods make up some 70 percent of the past two and a half billion years, and are called Greenhouse Earth. They can last hundreds of millions of years, with CO2 levels 10–20 times higher than today, and no ice anywhere on the planet.

During a Greenhouse interval, Earth actually explodes with life.

The age of dinosaurs happened during a Greenhouse. Land animals covered the continents. Reptiles swam in Arctic seas. Birds, mammals and flowering plants first appeared.

It’s been colder the other 30 percent of the past two and a half billion years, called Icehouse Earth. Life struggles in the most severe of these times.

Within Icehouse periods, Earth has shorter cycles of glacials and interglacials.

Glacial periods last about 80,000 years, when ice sheets cover large parts of the continents. Interglacials last for 20,000 years or less, and ice retreats toward the poles.  

We’re living in a mild interglacial of a long-term Icehouse now. Temperate climate for many millennia has allowed the human population to expand to what it is today.

Human activity may be accelerating warming, but historical climate patterns suggest that within a few thousand years we could enter another glacial period, when ice would slowly advance again from the poles.

Why we shift from Icehouse to Greenhouse, and glacial to interglacial, are important concepts, which we’ll explore on another EarthDate.

This natural gas, mostly methane, is frozen in water in a form we call methane hydrates. The methane came from decaying organic matter or migrated up from deeper natural gas deposits, and was then trapped in very high concentrations in frozen layers of sediment at high pressures.

When brought to the surface, the hydrates melt, releasing around 160 times their volume in natural gas.

This sounds like a very promising energy source, and companies and countries, especially those with limited resources like Japan, are trying to recover the gas.

But test plants have produced very little. This is partly because processing methane hydrates is a new and difficult engineering challenge. And partly because we know very little about them.

To study methane hydrates, scientists have built special high-pressure, low-temperature labs, where they can be kept in their frozen state.

One innovative project in Alaska is trying to pump in liquid CO2 under high pressure to liberate the gas. If successful, this new process could make methane hydrate deposits not just an energy source but a place to sequester carbon.

Eventually, engineers will probably figure out cost-effective, low-impact ways to produce methane from methane hydrates—one more reason that natural gas will likely play a larger role in our energy future.

To create a cave, Mother Nature needs three things: water, rock that can be dissolved by it, and lots of time.

Rainwater, as it falls through the atmosphere, picks up carbon from CO2 to become a weak carbonic acid. By the time it hits Earth, it’s about as acidic as coffee. As it percolates through the soil, it picks up more carbon from decaying plants, becoming a slightly stronger acid.

If the rock below the soil is limestone, gypsum, or dolomite, the water can dissolve along tiny cracks. Over many thousands of years, the cracks become channels, then tunnels, and could eventually become caverns.

Water might also mix with hydrogen sulfide gas seeping up from natural oil and gas deposits to form sulfuric acid, which can also dissolve the rock.

Protected from daily and seasonal changes on the surface, caves can maintain a stable temperature and humidity.

In these delicate environments, the remains of ancient animals and humans, which could have quickly decayed on the surface, have been preserved for millennia. Deeper, more isolated caves have preserved bacteria and microbes undisturbed for millions of years.

These qualities make caves important sites for researchers—natural time capsules. There’s probably an amazing cave near you, so take a trip and get to know your Earth.

Neanderthals, or their direct ancestors, migrated out of Africa and into the Middle East and Europe around 250,000 years ago. Soon they were well adapted to the environment.

Large eyes helped them see in the longer nights and darker winters. Stout bodies helped them retain heat and handle large prey, and provided space for the large liver and kidneys needed for a diet heavy in protein.

Their brains were as big as ours but spent processing power on their greater visual and motor abilities. This may not have allowed them to develop higher communication or conceptual thinking to match ours. Which may have been their downfall.

Modern humans arrived on the scene 45,000 years ago, less physically adapted but more mentally adaptable.

We had cooperative hunting methods superior to the Neanderthals’, allowing us to out-compete them for food and perhaps reducing the large herbivore populations that they depended on.

We also had superior tools and weapons. When there were conflicts between the groups—as there have been among tribes throughout history—our superior technology probably allowed us to prevail.

But we weren’t only fighting. There must have been considerable interbreeding, since we can find 1 to 3 percent of the Neanderthal genome in modern man.

Which means the Neanderthals never completely disappeared. A little bit of them is alive in us today.

Why? It’s mostly because we’re pumping more water into the ground.

The boom in U.S. oil and gas production over the last decade has brought many more oil wells —which also produce water.

Most is naturally occurring in the formation and some was injected by operators to allow or improve the recovery of oil and gas.

In both cases, the water will likely have picked up salt and other minerals from the rock, making it many times saltier than seawater.

Operators may reinject this water to continue to liberate oil and gas.

But more often, there’s too much to handle. So it’s trucked or piped to disposal wells, where it’s pumped down into deep saltwater reservoirs.

Adding large volumes of wastewater increases the pressure in these rock formations—which can allow natural faults to slip more easily than they normally would, causing earthquakes.

To address these quakes, regulators and the petroleum industry are monitoring disposal wells and shutting down those that could cause damaging seismic activity. And they now think that managing wastewater injection more carefully should help.

There’s still more work to be done, and university research centers like the Bureau of Economic Geology are conducting major studies, with the aim of minimizing the risk of earthquakes while maintaining the benefits of domestic energy production.

No, it’s not a new brand of bottled water, imported from the days of dinosaurs.

Fossil water came from melting ice sheets, ancient lake systems, and a generally wetter climate tens to hundreds of thousands of years ago.

It percolated into porous rocks, which were then buried under deep layers of sediment, where it was sealed off from the surface, and there it stayed.

Until farmers discovered it. And in the second half of the 20th century, they started drilling wells into fossil aquifers and pumping like mad, turning sunny dry places into acres and acres of green farmland.

Crop supplies boomed. Food became cheaper and more plentiful, grown in formerly parched places like California and Kansas and shipped around the world for people like you and me to eat, ingesting fossil water with it.

The trouble is, fossil water is a finite resource, and new studies suggest that many fossil aquifers may become depleted this century, so that we won’t be able to rely on them any longer.

This could mean that the crops that depend on them could become less plentiful and more expensive again.

All the while, population will likely increase. The climate will likely warm. Our demand for water will continue to climb.

Which means we’ll have to adapt to the lack of fossil water just as we adapted to its discovery. This time with more efficient crops and farming methods—and more efficient use.

So, a lot of work has gone into trying to store excess electricity, to use later when we need it.

The obvious solution, giant batteries, is still too expensive for most applications and has environmental implications. This has led scientists to look for other ways.

One method uses surplus power to compress air and pump it into old salt mines. The salt tends to seal cracks in the walls, making the mines airtight.

When needed, the compressed air can be released to turn a turbine. Or it can be used as the intake air for a natural gas power plant, making the plant more productive.

Another way to store excess energy is to pump water uphill, into existing reservoirs, and then release it through hydroelectric dams when power is needed.

This method was pioneered 100 years ago in Italy and Switzerland, and is used today around the world, and in many U.S. states like Michigan.

On the Chilean coast, they’re even experimenting with using solar energy to pump seawater up a cliff, where it could flow down to make power at night.

These solutions don’t make economic sense unless the electricity is very cheap, and the reservoir was already built for another purpose.

But when those two things are present, pumping air and water to store energy plays a valuable role in balancing the grid to meet our ever-changing power demands.

The valley floor is 20,000 sq miles of some of the most fertile soil on Earth. Here, the sun shines 300 days a year. More than 250 different crops grow, worth $17 billion per year. 

The valley was developed into farmland around the turn of the twentieth century. When farmers arrived, they began to drill wells into the fresh-water aquifers below.

By the 1930s, scientists began to notice an impact. Some of the aquifers, with their water levels and pressure drawn down, compacted. This meant they would never refill to earlier levels, and the land above them subsided.

This continued into the 1970s, when sinking land, up to 30 ft in parts of the valley, had damaged roads, bridges, and buildings so dramatically that California spent millions to repair them and built canals to bring in water.

The problem was alleviated—until conservation elsewhere in the state reduced water in the canals and valley farmers pulled hard on their wells again.

The wells remained unregulated until 2012, when California passed serious water legislation. It will be decades before it’s fully phased in, but the hardest-hit areas are being addressed now.

In the meantime, the valley floor and the water table continue to fall.

Flowering plants evolved 100 million years ago, and within 30 million years dominated the planet. Today, there are almost 400,000 species.

One reason for their global success is their remarkable fertilization system.

A single flower can produce hundreds of thousands of pollen grains, which can be distributed by the wind, insects, or animals, fertilizing other plants miles away.

Each plant produces a distinct-looking pollen grain. And each place on Earth, even each square block or backyard garden, has a distinct mix of plants.

By studying the mix of pollen grains found on a person, animal, or object, scientists can now tell precisely where they have been.

And since pollen is highly durable, outlasting the plants that produced it by thousands of years and surviving in the fossil record for millions, scientists can use it for ancient detective work.

Recently, paleontologists used fossil pollen in the digestive tracts of dinosaurs to tell what they ate and where.

Forensic palynologists now use pollen found on murder victims and suspects to place them in the same location, or even to discover where bodies have been hidden.

The new science of palynology is cross-pollinating many other fields, allowing a deeper understanding of Earth.

In the Arctic winter, the earth is frozen, from tens to thousands of feet down.

In summer, the top several feet melt, creating a so-called active layer where plants can take root.

Below that is permafrost: frozen soil that contains a great deal of ice. For these regions, it’s like bedrock—stabilizing the active layer and providing a solid footing for buildings.

But as the melting reaches deeper into the ground, the permafrost is not so permanent and is becoming unstable. Roads in Alaska and Canada are beginning to undulate and ripple, and runways are at risk. Foundations are shifting, making some buildings and houses unusable. Surface water drains and floods unpredictably.

What widespread effects could this have?

Permafrost, like regular soil, contains organic material from dead plants and animals.

As it melts, the organic matter decays, releasing CO2 and methane, both greenhouse gases. This could create a feedback loop of continued greenhouse gas release and further warming.

But melting permafrost is also creating a deeper soil layer, which may allow forests to replace tundra. In other places, it’s toppling existing forests and replacing them with wetlands. These would absorb CO2.

With permafrost covering nearly a quarter of the Northern Hemisphere, scientists are keeping a close eye on these changes and how they impact climate models.

The earliest art supplies we’ve found—abalone shells full of ground ochre and charcoal—were in the Blombos Cave in South Africa, and are up to 100,000 years old. But we haven’t yet found paintings to go with them.

By 40,000 years ago, tribes in Europe, Australia, and Indonesia painted images of hunters and herders on cave walls, and had expanded their palette to include many colors.

Pigments for these paints included blood, sap, berry juices, dried plants and roots, and many minerals.

Iron oxide pigments were highly valued for their durability, and prehistoric mining trails around the famous Lascaux Cave in France suggest that, 25,000 years ago, painters traveled many miles for these materials.

Early artists mixed their pigments into paint using water, saliva, urine, or animal fats. They then applied them with fingers, brushes, or by blowing them through hollow bones, like today’s airbrushes.

The Egyptians continued the modern advancements, mixing paints with binding agents like egg and began painting on plaster.

Greeks and Romans expanded upon these techniques, to create a painting style not matched till the Renaissance—when Italian artists made paint with plant oils to create works of astonishing color and depth that still captivate viewers today.

In the 1600s, a bishop worked backwards through generations of “begats” in the Bible to come to a very specific date for Creation: October 26, 4004 BC. At 6 PM.

In the 1700s, scientists developed their own theories. Recognizing that different layers of rock represent different periods in Earth history, they calculated a much looser estimate: 1 million to 1.6 billion years old.

By the early 1900s, scientists began to understand radioactivity, and found that each radioactive element has a half-life—a specific amount of time it takes to lose half its energy.

They could use these half-lives to more precisely date Earth’s rock layers, pushing the age of the oldest ones to 3 billion years.

With improved dating techniques, we now find rocks between 3.5 and 4 billion years old on every continent.

But there are limits to this method. The surface of Earth is always eroding and renewing itself, and old Earth rocks tend to get recycled. To reach back further in time, we needed a place of the same age, but undisturbed by plate tectonics, like the moon.

The oldest rocks we’ve found there date to around 4 and a half billion years. By studying these, and meteorites that landed on Earth from within our solar system, we’ve arrived at an age for Earth of 4.55 billion years.

That ancient history is still widely accepted—but it has a few new wrinkles.

Archaeological records now show that humans left Siberia 25,000 years ago but didn’t arrive in North America till 15,000 years ago. Where were they for 10,000 years in between?

New research suggests they were living in the Bering Strait, in a now-submerged land called Beringia.

During the peak of the last Ice Age, much of Earth’s water was held in continental ice sheets that caused ocean levels to drop 400 ft. The land of Beringia was exposed, as much as 3 million square kilometers.

It appears humans were trapped in this inhospitable terrain by glaciers to the east and west.

This great frozen tundra would not have supported the bison and mammoth that other early humans depended on. But it could have sustained caribou.

Perhaps more important, it held arctic oases of trees and brush, enough to provide shelter and firewood for the Beringians, who survived 10,000 years of winter by burning wood and animal bones.

They stayed in Beringia long enough to become genetically distinct from their Siberian ancestors, which we see in DNA analysis of Native tribes in both North and South America— the majority of whom descended from the Beringians.

It’s a remarkable testament to human resilience.

El Niño is simply warmer-than-normal water in the Pacific, off South America. It was first noticed by sailors in the 1600s, who named it after the Christ Child since it came in December.

We now know that El Niño lasts several months to several years, returns every 2 to 7 years, and is caused by atmospheric pressure.

In a normal year, high pressure over the Pacific and low pressure over Australia and Indonesia form trade winds. These blow west across the Pacific, pushing warm surface water with them—which brings humidity and rain to Australia.

Meanwhile, cold water from the deep replaces the exiting warm water, replenishing nutrients and fish stocks along South America.

But in an El Niño year, the high- and low-pressure areas are reversed, and trade winds stop.

Warm water stays put. Australia and Indonesia get less rain. South America gets it instead.

The shifting temperature patterns alter the jet stream, which changes the tracks of seasonal rains.

This makes it warmer and drier in the northern U.S. and Canada. Colder and wetter in the southern U.S. And causes droughts as far away as India.

La Niña is a natural compensation—colder-than-normal water in the western Pacific—which sometimes follows El Niño and brings opposite weather effects.

In northern Canada, the Kidd Creek Mine is almost 10,000 ft deep. Here, miners search for copper, zinc, and silver ore in volcanic material that was once the floor of an ancient sea.

At the very bottom of the mine, they drilled an exploratory borehole even farther down to look for more metal ore.

What they found was possibly the oldest water in the world, trapped in the rocks for more than 2 billion years.

Why is this important? It provides a snapshot of Earth from that far distant time before there was anything but single-celled life on the planet.

And what was water like then? Very different.

The water from this ancient sea is eight times saltier than today’s ocean water. Trapped in it are helium, argon, neon, krypton, and xenon gases.

And, surprisingly, sulfur isotopes which show that ancient single-celled organisms must have lived in it long ago.

Scientists are still analyzing this ancient water, in hopes of better understanding not only our juvenile Earth, but also the types of extreme environments we may find elsewhere, like on the moons of Saturn and Jupiter, where there are vast oceans of water trapped beneath ice sheets.

If basic life forms existed in our ancient water, without sunlight or any contact with the surface, it is possible we will find them in other places, too.

About 6 million years ago, growing ice sheets in Antarctica began to trap Earth’s water and lower sea levels. Waters in the Strait of Gibraltar, that narrow channel between Spain and Morocco, began to recede.

Freed from the weight of the water, the land began to rise. Which caused a feedback loop of shallower waters and more rising seafloor, till the strait … became a dam, and the Mediterranean was separated from the Atlantic.

Within a thousand years, the Mediterranean had almost completely dried up, leaving a desert basin nearly 2 miles deep. Over several hundred thousand more years, it was partially filled and dried out again many times, leaving layers of salt and gypsum, in some places more than a mile thick.

Around 5 and a half million years ago, the major ice sheets began to melt, and a rising Atlantic breached the dam. Water rushed into the Mediterranean, carving a channel a mile wide and 100 miles long.

Scientists estimate it filled the entire Mediterranean again in less than 2 years, and in short order, one of the Earth’s most inhospitable places became one of its richest, teeming with life.  

Ever since Darwin found microbes in dust over the Atlantic, they’ve turned up in ever-stranger places:

In dust plumes over mountains. In high-altitude snowfields. And in the tops of clouds.

This means, of course, they’re also in rain. Scientists have identified thousands of species of microbes and fungi living in rain and clouds—able to withstand the harsh temperatures, low oxygen and punishing radiation of the atmosphere.

What we didn’t expect is their complex relationship with clouds and rain.

Clouds are usually born at high altitude, where it’s cold enough for ice crystals to form. To do that, they need a nucleus to form around. Nuclei can be inorganic particles, like dust, salt, or ash. Or they can be organic particles, like microbes.

Recently we’ve discovered that many cloud-dwelling microbes create proteins that mimic the structure of ice crystals, allowing ice—and therefore clouds—to form at higher temperatures and lower altitudes.

As the ice crystals grow and become heavy, they fall through the cloud to become snow, sleet, or rain, carrying the microbes down with them.

On Earth, many of these microbes feed on plant populations, which die and dry up, and the microbes are carried by the wind into the atmosphere again.

This cycle transports microbes around the world, forms more clouds and, with them, more rain.

The crust of the Earth is composed of many tectonic plates, which are always moving.

As the plate boundaries collide, grind against, or pull apart from each other, the crust cracks, creating fault zones.

As stress builds up, the plate boundary faults can open or slide, causing natural earthquakes. The vast majority are too small to feel, but some can be major.

Sometimes human activities can trigger an earthquake, causing a fault to move earlier than it naturally would. In 2017, some British scientists decided to catalogue these.

They found that about half were due to extraction—of mining products, groundwater, or oil. Removal of material changes the stress, which can cause faults to move.

Another quarter were caused by loading the Earth’s surface where it was not loaded before, such as reservoirs held behind dams, which can add stress to faults.

The last quarter happen when fluids produced from the Earth are injected back into it, like in a disposal well, where wastewater from oil or gas production changes the pressure conditions, sometimes causing the fault to slip.

This last type gets a lot of attention these days, and we’re studying it extensively at the Bureau of Economic Geology, where I work.

Ever since humans have had large-scale industrial processes we’ve been interacting with Earth’s natural earthquake cycle … in ways we’re just now coming to understand.

There are 17 REEs, with funny names like gadolinium and dysprosium—and all of them are metals.

Their special magnetic, thermal, and corrosion-resistant properties have led engineers to use them in our most familiar electronics.

The rarest ones are still 200 times more plentiful than gold. And the most common are as abundant in the Earth’s crust as nickel, zinc, or lead.

The challenge is that they’re rarely concentrated enough to mine. And when they are, it takes heavy processing with heat and acid, which produces salty, radioactive wastewater.

California was the largest producer of rare earth elements—till China entered the market.

Lower labor costs and looser environmental regulations allowed China to produce such a large supply so cheaply that U.S. mines closed.

With rare earth elements common and cheap, engineers used them in thousands of products.

But once China dominated the market, they began to raise prices and limit supply, to apply political pressure to electronics makers, like Japan.

But this backfired: Higher prices encouraged mines in other countries to reopen and discouraged engineers from using rare earth elements in new designs.

Which goes to show that rare earth elements, like all resources, are subject to the laws of economics.

Supply often depends on how much we’re willing to pay. If the price climbs beyond that, we start looking for alternatives.

You probably guessed that I’m not talking about Everest. It’s still the tallest when measuring purely by height above sea level, or altitude, at just over 29,000 ft.

But by other metrics, there are other contenders.

If you measure from the center of the Earth, the highest mountain is near the equator, where the Earth is 21 km wider than at the poles. By this measure, the tallest is the volcano of Chimborazo, in Ecuador.

But, if you’re starting at the base of the mountain and measuring to the top, the tallest—by a wide margin—is another volcano: Mauna Kea on the big island of Hawaii.

Its summit is just shy of 14,000 ft above sea level, the ocean around Mauna Kea is almost 20,000 ft deep, and the base of the volcano is on the seafloor. This makes Mauna Kea nearly 34,000 ft from tip to toe, a full mile taller than Everest.

Its low humidity and long distance from civilization make Mauna Kea an excellent astronomical observatory, with 13 international telescopes at its summit.

There are roads leading up to them, so if you’re looking for an 8-hr-straight-up bike climb followed by a blistering white-knuckle descent, Mauna Kea may be your kind of mountain.

The cardinal, for instance, has the range of a piano, though higher on both ends. And he can span it in a tenth of a second. No human can come close.

The wood thrush can sing one note, a different note on top of that, and trill them both independently. It’s like a soprano duet in one 2-oz animal!

How can they do these incredible things? The secret is their voice box.

Our larynx has one chamber. Theirs, called the syrinx, has two. Ours sits in our throat; theirs, at the base of their trachea. At that location, each chamber has access to a lung.

In this way, the most accomplished bird singers can control each side of their voice box separately, even take small breaths in one side while singing from the other, to keep their song continuous.

If that weren’t enough, some birds know up to 1,000 different songs.

You may remember from a previous EarthDate that for most of Earth’s history, animals couldn’t hear sounds—or make them. So it’s particularly impressive that birds have developed this ability.

In fact, one of the ways we know that ancestors of modern birds lived through the asteroid extinction that wiped out the dinosaurs is that we’ve discovered fossils from before the impact with a voice box similar to those of today.

The syrinx is one of nature’s greatest hits. It may be an oldie, but it’s a goodie.

In another EarthDate, you heard how lightning is essential to life on Earth. It frees up nitrogen in the atmosphere to make it available to plants, which form the base of our food web.

For that to happen, you’d think there must be a lot of lightning. And you’d be right.

Storms around the world produce about a billion and a half lightning strikes each year—which hit about 20,000 people. Of them, only 10 percent, or 2,000, die.

That’s a lot, but it makes for pretty slim odds—about 1 in a million.

To make them even slimmer, try these simple guidelines:

First, the obvious: don’t go out in a lightning storm. Most buildings have lightning rods, wiring, or plumbing that will guide the lightning safely into the ground.

But stay out of the shower and off the landline. Plumbing and electric lines could carry a charge.

If you are caught out, avoid high places, where you’re closer to the clouds.

Also try to avoid flat open spaces, where you might be the tallest object.

And, large trees—lightning can vaporize the water inside them, causing them to explode.

If you can get to, or stay in, your car, that’s a good place to be. The frame, wheels, and dripping rainwater can carry the charge to the ground, leaving you insulated.

Earth is the only planet we know of where the three phases of water—solid, liquid, and gas—are present on its surface.

That’s partly because those three phases exist in a narrow temperature window. And the middle phase—liquid water—corresponds to much of Earth’s surface temperature.

This allows our oceans to exist, which are the key reservoirs of the hydrological system. Winds moving across oceans lift huge volumes of water vapor—seven times more than simple evaporation could.

Converting liquid water to gas distills it, leaving salts and impurities in the sea and carrying pure water vapor into the atmosphere. It rises to form clouds and rains down elsewhere.

Three-quarters of that rain falls back into the ocean. The other 25 percent falls on land, where it’s used by all terrestrial life.

But it’s also one of the most powerful forces eroding the surface of Earth.

Gravity pulls rainwater downhill, and over a few million years—a blink of an eye on Earth’s time scale—it can flatten mountains and carry them in rivers, grain by grain, to the sea.

If frozen into glaciers, water becomes a river of ice and rock, grinding down the earth even faster.

The amazing life-giving, planet-shaping properties of water are what make Earth what it is, and we’ll talk a lot more about it on EarthDate.

Well, here’s a famous beast that started as a tiny elephant.

During the Pleistocene ice ages, polar ice and continental glaciers held more of Earth’s water, causing sea level to fall.

During low sea-level periods, elephants from Africa walked and swam across a nearly dry Mediterranean to Europe. Once seas rose again, some were trapped on islands like Sicily.

When a population gets stuck on an island, it will often overstress its food reserves and be forced to adapt—something called island rule.

These elephants shrunk to survive on less food, and on Sicily got as small as 3 ft tall and 250 pounds.

Once adapted, they did quite well, with no natural predators…

That is, until man arrived, 11,000 years ago. Overstressing their own food reserves, early tribes hunted the small elephants to extinction.

Some of their bones ended up in caves, where tribes lived or cooked. And thousands of years later, the Greeks discovered them.

The elephants’ skulls were about twice the size of a human’s—with a single hole in the middle where the trunk would have been.

Having never seen an elephant, the Greeks imagined these were the skulls of giants with one large eye: the dreaded cave-dwelling Cyclopes—which then appeared in Greek mythology and rose to fame in Homer’s Odyssey.

Today, scientists believe they found fossils and, unable to explain them, gave them exaggerated features of the animals they knew and found places for them in folklore.

For instance, we know Greeks and Romans collected fossil bones. They believed these once belonged to their gods and warrior heroes, who were hailed as giants when the huge bones were found.

These fossils, now known to come from mammoths, were displayed in the Roman capital as late as AD 500.

Long before then, different cultures told stories of gryphons, which were part lion, part eagle and protected Earth’s gold.

Where might this story have come from?

In the Gobi Desert, gold would often erode into streambeds with fossils of Protoceratops. Their skulls somewhat resembled contemporary lions, but with a large eagle-like beak.

Earlier still, dragons appeared in Chinese mythology. While many experts today don’t see a direct fossil connection, there’s an ironic link to the present day:

Many villagers still believe in dragons and grind fossilized “dragon bone” into medicines, as they have for 2,500 years. Paleontologists can often follow the sources of apothecary “dragon bone” to find new fossil beds.

No doubt there are some cases where mythical beasts sprang purely from the imagination, not fossil discoveries. But on a future EarthDate, we’ll look at one famous myth that almost certainly did.

So you may be surprised to hear that scientists have discovered a new continent—and New Zealand is part of it, after all. In fact, it’s one of the only parts of what’s now called Zealandia that’s above sea level.

Most of Zealandia, which is almost two-thirds as big as the continental United States, is more than a kilometer underwater.

That’s deep enough that you might be thinking, “That doesn’t sound like a continent.” Except the seafloor around it is 4 kilometers deep.

Antarctica, too, if you melted all the ice, would be just a few islands, with most of the western part of the continent submerged.

Which begs the question: what exactly makes a continent? The leading factors are its mineral content and density.

The seafloor is dense and heavy with iron, so it rides low in the mantle that supports all of Earth’s crust.

Continental crust is high in silica and aluminum. It’s less dense and much thicker than oceanic crust, so it floats higher in the mantle, like ice on a lake.

Most continents are large landmasses surrounded by a shallow ocean shelf.

But Zealandia is a small landmass surrounded by a large ocean shelf, having been pushed around, squeezed, then sunk by plate tectonic forces over millions of years.

Deserts have little rain, but if they’re near the coast, they can have fog—which you may remember is just a cloud on the ground, water vapor condensing around particles in the air.

In the Atacama, fogs often roll in from the Pacific, but the water droplets are too small to produce rain. So in the 1950’s, a professor began experimenting with ways to extract water from the cloud.

Following his lead, the villagers of Peña Blanca have strung a series of nets in the mountains. Together, they condense more than 2,000 gallons of water from the fog each day, which is carried by aqueducts into the village.

This water serves people, livestock, vegetable gardens—and an award-winning microbrewery. Their beers are famed for their light body, which some attribute to the lack of minerals in the cloud-borne water.

Chilean researchers estimate that collecting just 4 percent of the water from the Atacama fog would meet the needs of all the communities in the desert, and that a 3-ft by 5-ft net could provide enough water for one person per day.

For these reasons, villages in many countries are now building fog nets, and they could be an important source of water—and beer—in coastal deserts around the world.

In 2003, NASA took the same technology to the Atacama Desert in Chile and got the same reading. Was there really no life there?

And by extension, no life on Mars?

You might think that the driest place on Earth is the Sahara. But they’re actually polar deserts, like the McMurdo Dry Valleys of Antarctica, and high deserts, like the Atacama. There are places there where it hasn’t rained in 500 years—if ever.

Surprisingly, the driest deserts are cold, not hot. That’s because cold air holds 20 times less water vapor than hot air.

Though average temperatures in McMurdo are below freezing, the Atacama averages 70 degrees—but it’s in the rain shadow of both the Andes and the Chilean Coastal Range. It’s at 8,000 ft, where the air is very thin. And it’s near the equator, where solar radiation is extreme all year long.

This is the most similar environment on Earth to Mars, which is why NASA is testing old and new Martian exploration technology here.

While the Viking equipment missed any signs of life in the Atacama, new understanding of extremophiles—life found in extreme conditions—led NASA scientists to look beneath the soil and within rocks, where they found photosynthetic bacteria.

And if life can exist here, in the most inhospitable place on Earth, we might also find it on the next mission to Mars.

A bite on a fossil is not that unusual, but this one helped settle an argument.

Over the past few decades, some paleontologists maintained that T. rex was a ferocious hunter.

Newer theories pointed to his useless forelimbs, small eyes, and huge olfactory chambers.

He wouldn’t have been able to grasp prey and may have had poor vision—but he would have been able to smell a rotting carcass from miles away. In other words, he was likely a scavenger.

But the hadrosaur tail vertebrae in this fossil were fused together around a T. rex tooth—the wound had healed.

This meant that the hadrosaur was alive when it happened, and lived on. Which strongly suggests that T. rex did in fact chase and catch it—almost.

This brought up another question: given his weaknesses, how did the tyrannosaur do it?

A different set of scientists analyzed the leg mechanics of T. rex for bone stress. Proponents of “T. rex the hunter” had pointed to his speed, previously estimated at over 30 miles per hour.

But this new research suggests that the foot bones, carrying his 7 tons of weight, would have shattered at that pace. The tyrannosaur’s top speed was probably just 12 miles per hour.

And maybe that’s why the duckbill got away—T. rex may have been an occasional hunter, but maybe not a very good one.

In many European cultures, he was a man banished to the moon for stealing from his neighbors—or for working on Sunday. (Good thing that’s not a banishable offense today!)

Coastal Germans, recognizing the moon’s tidal connection, believed he was a giant who poured water on Earth to create high tide.

In Norse legend, the man kidnapped two children to have them fetch that water, a story that would become Jack and Jill.

In the Southern Hemisphere, however, the man’s face is upside down, which makes it look like a rabbit—with legends all its own.

The eyes of the man and the body of the rabbit are actually basalt flats caused by ancient lava flows. But why do all people on Earth see this same view?

The answer is something called tidal locking—most moons are tidally locked to their planets.

Soon after the moon formed, the powerful pull of Earth’s gravity created a bulge near the moon’s equator.

Gravity kept pulling the bulge toward Earth, slowing the moon’s rotation till it was perfectly in synch with the moon’s orbit around Earth, meaning that only one side of it faces Earth, and always will.

So what exactly is on the other side of the moon? You’ll have to wait till another EarthDate to find out.

The term “sand” just refers to the size of the grain. It can be made of many materials, but the sand we value most is made of quartz.

We use it to make glass, computer chips, roof shingles, paints, sealants, cosmetics, and much more.

But we use it most in concrete, which is about two-thirds sand. There are hundreds of tons in the average American house—and billions of tons in cities. And therein lies the rub.

Because sand is so heavy, it’s expensive to transport, meaning most sand used in buildings is local.

And the rapid growth of new cities, particularly in China, India, and other developing countries, has used up much of the high-quality local supply.

Beach sand is not a good choice for concrete—the salt can corrode the reinforcing steel. Yet some coastal cities and island nations have stripped their beaches bare for the building trade, leaving only rock.

Other communities, like Dubai and Phoenix, use their local desert sand, which is often poor quality, as well. It’s high in clay, chalk, and iron oxide.

Shortage of good-quality sand has led China to begin importing it. Elsewhere, like in India, a black market has sprung up, complete with sand mafias!

In the future, we’re likely to see a growing global trade in this surprisingly precious commodity.

All that water was due to where Venice is built—in the middle of a lagoon. And why was it built there?

In the fifth century, Roman farmers, fleeing invaders, moved out to fishing huts on a string of low mud islands. Battered by tides, they built houses on stilts.

But their protection worked. While barbarians pillaged Italy, Venice thrived. Their settlement grew into a city, which grew into the greatest naval power in the Mediterranean—with the whole thing built on stilts.

Over the centuries, sediments beneath the city gradually compacted. The Venetians responded by jacking up their buildings farther.

But in the twentieth century, drilling and extraction of groundwater and natural gas caused the city to sink faster, while the Adriatic Sea level rose.

Tidal flooding became so frequent that Venice built a system of 79 enormous steel gates at the inlets to their lagoon. Each gate is 100 ft tall and weighs 300 tons. It rests flat on the seafloor—till an overly high tide is predicted.

Then, Venice pumps the gates full of air, and they slowly stand up, able to hold back 10 ft of ocean surge. When the threat is over, they sink back to the seafloor.

There are many other subsiding cities, like New Orleans, Miami, and Jakarta, keeping a watchful eye on the sea—and on the amazing gates of Venice.

And it left many wondering: could it happen again?

Harvey was a so-called “500-year event.” This means that meteorologists project 1 in 500 odds that a flood of that size will happen in a given year.

The incredible thing is that Harvey was the third 500-year flood in Houston in just 3 years. The odds of that happening are very long indeed.

This suggests that the probability system may need to be revised, and that in the future, severe floods may be more likely.

There is no “normal” in nature. It’s always changing. Nature doesn’t adapt to humans; humans must adapt to nature.

Houston is located on a marshy plain. Its soils don’t drain well ... but they hardly drain at all when covered in concrete or asphalt. Houston has grown successfully, but future plans should maximize green space and minimize impermeable cover. 

Since its land is flat, the rivers and bayous that drain Houston are slow moving, and prone to overflow. The city must accelerate efforts to widen and improve them, and consider barriers to block storm surge from pushing water back up them.

As population grows, there will be a temptation to expand into flood-prone areas. The city has been warning developers against this but should step up efforts.

The good news is, with careful planning and management, Houston should be able to minimize the impact of future storms.

What you may not have heard is that Earth has been emitting and storing carbon for millions of years, cycling it between sky, sea, soil, and rock.

Deep in the geologic past, atmospheric carbon dioxide was 10 times higher than today. Then ancient ocean life began to use it.

Early marine organisms used CO2 dissolved in seawater for photosynthesis, forming the base of the food chain. Other organisms used it to build their exoskeletons and shells.

When they died, their carbon-rich remains sank to the seafloor and were buried. Very slowly, carbon was being stored within the earth.

Millions of years later, plants evolved and dramatically changed the carbon balance. They began to turn huge volumes of atmospheric carbon into organic carbon like carbohydrates and cellulose.

Some organic carbon goes back into the atmosphere or the soil. Some gets buried and becomes part of sedimentary layers and, with enough pressure and time, can be cooked into hydrocarbons—fossil fuels.

Today, the burning of fossil fuels is moving ancient carbon stored in the earth back into the atmosphere. Researchers are studying different ways to sequester that CO2, and we’ll talk about that on a future EarthDate.

There were times in Earth’s history when there was no polar ice at all. And many times, like today, when ice sheets formed at the poles.

In the Antarctic today, ice sheets cover 5 million square miles with over a mile of ice that’s up to 1 million years old. In subglacial polar lakes, this life may not have seen the light of day for 20 million years.

This enormous quantity of ice has been shown to harbor microbes in huge numbers. Scientists estimate their total organic carbon biomass would be about ten times that of all humans on Earth.

And, perhaps not so surprisingly, with ice this old, the bacteria are ancient, too.

Viable species hundreds of thousands of years old have been discovered in ice, frozen there all that time in a sort of suspended animation.

But once liberated and revived in labs, some started to replicate as normal.

With them are previously unknown viruses, and certainly new microbes that are yet to be discovered.

And this has scientists both concerned and excited. With continued polar ice melt, some of these microbes could bring ancient diseases…while some could bring new cures for existing ones.

Of course, this has prompted research; and we’ll look into that in a future EarthDate.

The glass on the front is a special hardened type. It’s made of quartz, which may have come from the USA, and aluminum, which probably came from Australia. It’s then treated with potassium salts, likely from Canada.

For scratch resistance, it’s given a coating, made of iridium from South Korea and tin from Indonesia.

The colors on its screen come from rare earth elements, mostly from China.

Its microelectronics could include copper from Chile, silver from Mexico, platinum from South Africa, and tungsten from Russia. Its tiny capacitors use tantalum from central Africa or Brazil.

Your phone’s rechargeable battery is made of lithium, which may have come from Argentina; cobalt from the Congo or Zambia; and pure graphite from India.

Petroleum, from many sources around the world, is used to ship all these minerals to factories, where they’re assembled into parts, then shipped again to be assembled into phones.

If supplies of any of these elements, from any of these countries, were to be restricted, it could disrupt the price and availability of the phones that billions of us rely on. There are also serious environmental impacts to mining these minerals.

Recycling the billions of old phones will ensure we have materials available for new ones.

Well, it killed at least 8,000 people and sent another 150,000 to the hospital. How was this?

In the years after World War II, England had rebuilt its factories and power stations, and all were burning coal. London residents, too, were burning coal in their homes to keep warm.

But England had sold its premium coal to pay war debts and was using a poor grade with high sulfur content.

On a particularly cold winter day in 1952, with furnaces and fireplaces working overtime, a fog rolled in.

Fog is just a cloud on the ground. It forms when humid air cools and its water vapor condenses. This time, there was also a high pressure area that sat over London.

Together they trapped the coal emissions, and the fog became the “Great Smog.”

Sulfur dioxide in the smoke mixed with water vapor in the fog to form a dilute sulfuric acid. As the water evaporated, the fog became ever-more acidic and stank of rotten eggs.

Breathing it damaged lungs and led to serious lung infections.

Hospitals overfilled. People began dying in such numbers that undertakers ran out of coffins. Finally, 5 days after it began, wind blew the toxic fog out to sea.

Today, scientists are using lessons from the Great Smog to mitigate the effects of smog in China and other industrializing areas that depend on coal for electricity.

It’s a mystery.

In fact, we don’t understand the vast majority of the seafloor. Our maps of the moon, Mars, and even Venus are 50 times more detailed.

Near the coasts and continental shelves, where waters are shallow and boat traffic is high, we’ve used sonar from ships to build high-resolution seafloor maps. But these cover just 10% of the ocean.

The rest, with an average depth of 2.5 miles, is too deep for ordinary sonar, and too remote and dark for other types of visual mapping.

So we’ve resorted to measuring the ocean surface with satellites, then interpreting the seafloor from that. The best resolution we’ve been able to manage is a data point every 3 miles.

Exactly what’s happening between these points? We have little idea.

And this is a bit of a problem. The contours of the seafloor shape the paths of tsunamis and the direction of major currents that shape our weather.

When a cargo ship or a jetliner goes missing, we struggle to locate them.

Who knows what we might discover with a better knowledge of the deep ocean. New minerals and resources. New life forms. Things so new we can’t even imagine them.

This is partly because geysers are spectacular, and partly because they’re rare. There are only about 1,000 worldwide, and nearly half of them are in Yellowstone. Most others occur in just five countries.

Why are there so few? They require very specialized geology.

At the surface, they need caprock, to trap water. In the subsurface, they need fissures in the rock, so water can flow into and collect in reservoirs and cavities.

Below that, they need intense heat—all geysers are in volcanic areas.

The bottom of the geyser’s water column is closest to the heat, under higher pressure—which raises the boiling point. So the water keeps heating without converting to steam.

The heat travels up the water column, eventually reaching the top. There, the pressure is lower, so the water can boil.

As it turns to steam, it releases pressure on the water just below it. Which can now boil, releasing pressure on the water further down, and so on. This chain reaction produces huge volumes of steam, which erupt out the top of the geyser.

In large geysers, steam can carry thousands of gallons of boiling water into the air, in fountains that can last a few seconds to a few hours and reach heights up to 300 ft.

If you go to see one, prepare to be amazed. It’s one of nature’s greatest shows.

How exactly is T. rex related to the common house sparrow?

Around 230 million years ago, there was a group of dinosaurs called the theropods, which included the bipedal carnivores.

With their back legs used for movement, their front legs were free to specialize. In T. rex, they became, well, not much. But in other species they became grasping claws.

While T-rex and his cousins were getting bigger, the grasping-claw dinosaurs got smaller. One of these subgroups, the coelurosaurs, evolved two important things:

They became omnivores, so they could survive on a broader diet.

And they grew early feathers, perhaps to keep warm. Suggesting they may have also become warm-blooded, like birds.

With these traits in place, this group evolved rapidly. They got smaller still and developed early wings, for hopping and then gliding.

This was a huge advantage, which encouraged ever-more-capable flight. Over millions more years, they evolved sophisticated feathers and hollow bones.

Finally, to navigate in three dimensions and across huge areas, they developed greater brainpower and better communication systems.

When that asteroid hit Earth 66 millions years ago, it ended the reign of T. rex. But birds, with their new capabilities, flew on. So look for a little dinosaur on your windowsill.

The soil is a place where air, water, rock, and life intersect. It’s the surface we live on, farm in, build upon, and are often buried in when we die.

For dirt to be good soil, it needs some special ingredients: decomposed bedrock—which gives soil its minerals; organics—from dead plant and animal matter; and life—lots of it.

In a single shovelful of dirt there are trillions of creatures, from earthworms to bacteria, and thousands of feet of fungus.

Soil’s most important job is to provide plants their nutrients and a place to anchor their roots. But it does many other amazing things.

It absorbs, stores, and releases most of the water on Earth’s surface and filters it before it moves to an aquifer.

By managing water, soil limits surface runoff and flooding.

Soil stores and recycles minerals and other nutrients, so that living things can use them again and again.

It absorbs and emits gases like carbon dioxide, methane, and water vapor, constantly interacting with the atmosphere.

It even provides building materials, like sand for concrete, clay for bricks, and lumber from trees growing on healthy soil.

How we choose to take care of our dirt—how we farm it, keep it free from pollutants, and recognize that it’s a living ecosystem—impacts the health of all other life on Earth.

Glaciers form when winter snow does not melt in summer. Some of it lasts till next winter’s snow, which covers and compresses it.

More years of snow add more weight, which eventually compacts the layers into ice.

Glaciers that continue to add snow and weight eventually become heavy enough to move downhill. They bend, flow, and can even fold on themselves, and that movement could have destroyed our Swiss couple’s bodies.

But it didn’t. This glacier was very stable, not moving much, the amount of winter snow balanced with the amount of summer melt.

Instead, in the cold, very dry environment, the bodies essentially freeze-dried, preserving them there through the decades.

Until now: 2014, ’15, and ‘16 were warmer years and glaciers in the region have begun to shrink.

A patrol crossing the area, on one of their regular paths, found the remains of the couple melting out of the ice.

Their children, now in their 70s and 80s with children and grandchildren of their own, breathed a sigh of relief: they could finally lay their parents to rest in the town cemetery.

They chose to wear white to the funeral, rather than black, to symbolize the hope they always held out, to one day reclaim them from the mountains.

Not exactly a good reputation—so it might surprise you to know that lightning is essential to life on Earth.

Lightning forms when freezing water droplets fall through a cloud, carrying a small charge with them. Millions of falling drops eventually build up a negative charge at the bottom of the cloud.

When the charge becomes powerful enough, it slices through the air in a bolt of current, connecting to a positively charged area to neutralize it. This could be the ground below or, more often, the top of the cloud.

The bolt is just 1 inch wide and lasts one-fifth of a second. It travels at 200,000 miles per hour and heats the air around it hotter than the surface of the sun. This air expands very rapidly, and the shock wave is heard as thunder.

As lightning blasts through the atmosphere, it breaks apart nitrogen molecules. This allows them to combine with oxygen in the air to form nitrogen oxides. The rain dissolves these into nitrates, then carries them to Earth and into the soil.

Nitrates are the most easily absorbed form of nitrogen for plants, which require nitrogen to thrive.

And thriving plants are the base of the food web that all other creatures depend on.

Just another reminder that everything is interlinked on our amazing planet—and these connections can sometimes be shocking.

Scientists have been trying to determine what the prehistoric world sounded like by studying the sounds of modern animals.

Sounds of aggression, like roars and screams. Sounds of communication, like birdsong or a wolf howl. Perhaps most amazing, echolocation—used by bats and whales to find prey and avoid obstacles.

The organs required to make, and hear, these sounds had to evolve sometime. So scientists went looking for them in the fossil record. And here’s what they found:

For 90% of Earth’s history, the only sounds were natural phenomena, like waves and thunder. That would have made little difference to early life forms—because none of them could hear.

Then around 400 million years ago, crustaceans started making clicking sounds. Early fishes, looking for a meal, developed the ability to hear them.

It took land animals a long time to catch up. But by 200 million years ago, insects were chirping, early birds were honking, and, to track them, predators developed the tympanic eardrum.

So what would you have heard from that tyrannosaur? Well, not much. He might have been able to huff or hiss. But with no vocal cords, he couldn’t roar like in the movies.

And he’d probably be too far behind you anyway. Turns out T. rex may have been much slower than we thought. But that’s a story for another EarthDate.

But salt is a vital ingredient—for the function of our nerves, muscles, and organs.

Humans used to get their salt from eating wild meat. But as we began to rely on agriculture, adding salt to our diets became more important.

For cultures that lived near the sea, getting salt was easy. But the farther inland humans lived, the more salt became a scarce commodity.

Wars were fought over access to it. And salt mines, when they were discovered, were strategic resources.

Salt reserves form when seas dry up and their salt is left behind as thick layers.

Salt is different than any other sediment layer: it flows like glaciers at Earth’s surface and forms giant salt domes underground. 

As early as 3500 BC, a salt reserve was found in Poland. It became a center of commerce, and eventually the city of Kraków was built on top of it.

By AD 1200, miners had dug the mine more than 1,000 ft down, to include nearly 2,000 chambers. The miners began to build religious chapels in them, especially where there had been accidents.

The grandest chapel has furniture, statues, and even chandeliers, all carved from salt. The chapels are now a UNESCO World Heritage Site, so if you’re ever in Kraków, be sure to observe a quiet, if not salty, moment.

It all started 7,000 years ago, when the Sahara wasn’t a desert at all, but a land of huge lakes. The largest was the mega-lake Chad, bigger than all of our Great Lakes combined.

The mega-lake was home to a huge number of diatoms, algae-like plankton that form the base of the food chain. After algal blooms, billions of dead diatoms would sink to the lake floor.

When natural climate change caused the lake to shrink dramatically, it left behind the massive Bodélé Depression, which is now called the “dustiest place on Earth.”

This dust is rich with phosphorous from centuries of dead diatoms and iron from the lakebed. Each winter, winds blow down from the mountains of Saharan Africa and carry it high into the sky.

The dust then blows across the Atlantic in huge plumes and over the Amazon.

There, rising water vapor from the rainforest condenses on the dust particles and rains back down, rich in minerals, like fertilizer from the sky. The phosphorous and iron are essential to the vigorous plant health across the region.

Amazingly, at about the same rate that the Saharan winds carry it in, floods wash previous years’ phosphorous out of the soil, down river, and into the sea.

There, it feeds new algal blooms—completing a circle thousands of miles wide and thousands of years in the making.

As violent and frightening as landslides can be, they’re a natural part of the constant erosion and reformation of Earth. Most often, erosion is a very slow process—except about 400 times a year, when there’s a landslide.

They can creep downhill at just a few inches a day. Or they can build up speed, hitting nearly 200 miles an hour. Landslides can be massive, moving many cubic miles of earth in a single event. The wind they push in front of them can strip the leaves off of trees.

Landslides require both gravity and water. Natural erosion, or manmade activities like a roadcut, can make a slope overly steep or unstable. Too much water—from rainfall, snow, or even groundwater—can then weaken the internal cohesion of the soil.

After that, it’s just waiting for a trigger. That could be a natural tremor, from an earthquake or even thunder. Or it could be manmade, like vibrations from a mining operation or a train.

Studies of the Washington slide have helped us better understand all these contributing factors. And as our knowledge of landslides continues to grow, hopefully we’ll get better at getting out of their way.

Fifteen years ago, NASA launched the Gravity Recovery and Climate Experiment, or GRACE. It’s a pair of satellites with a codependency issue. Rather than measuring Earth’s surface, they keep track of each other. In particular, their exact distance from one another, down to the micron.

When the first satellite passes over a place on Earth with greater gravity, it speeds up very, very slightly, and the distance between the satellites increases—by less than the width of a human hair. When it passes over an area with lower gravity, the distance decreases.

By tracking the expanding and contracting distances between each other, over 2.5 billon miles of Earth orbits, the pair has given us a more accurate picture of our varying gravity than ever before, which has revealed something very important.

Humans have never been able to measure groundwater well. But by sensing the shifting gravity as the water is depleted, the satellites have found that, under many cities in deserts, groundwater reserves have declined by two-thirds since they started measuring, putting these communities at serious risk.

With this remarkable data from space, we can better manage our water resources here on Earth.

Working against it keeps our muscles toned, and the rest of us…not so toned. But it keeps us standing upright, keeps water in our glasses and in the oceans. In fact, Earth as we know it couldn’t exist without gravity.

All objects exert a gravitational pull on other objects. The strength of this pull is determined by the object’s size and density.

The sun has more gravitational pull than Earth, which holds Earth in orbit around it. The moon has less than Earth—and thus orbits around us—but still has enough gravity to pull on Earth’s water, causing tides.

If Earth had a smooth surface, and were the same density in all places, gravity would be the same everywhere. But it’s neither of these things.

If you’re standing next to a mountain and holding a lead weight on a string, that weight would not hang perfectly straight but would be drawn slightly toward the mountain. Not enough for you to notice, but measurable with a sensitive instrument.

Mountain ranges in general have stronger gravitational pull than, say, oceans, since rock is denser than water. It’s the different densities of different places on Earth that cause Earth’s gravity to vary.

We’ll explore the surprising things that changing gravity reveals on a future EarthDate.

Its powers were recognized by early cultures, from the Greeks to Native Americans. And for decades it has been used as a pharmaceutical drug.

Lithium is highly reactive—it’s one of the few metals that will easily burn. If you try to put it out with water, it reacts violently, as it splits off hydrogen gas, which also burns.

When lithium burns, it creates a crimson light—which you’ve seen whenever you’ve watched a fireworks show. Lithium makes their signature red color.

Lithium is so reactive it’s typically stored in mineral oil. But when it enters the human body, often as a much less reactive lithium salt, its incendiary personality does a 180.

In a process we don’t completely understand, it seems to moderate the flow of electricity and promote the overall health of our nervous system. The result is a calming effect.

This has led doctors to prescribe lithium as a successful treatment for bipolar disorder. Studies have even found that cities and towns with higher levels of lithium salts in their groundwater have markedly lower levels of depression, suicide, and violent crime.

A very surprising fact—which has led some scientists to recommend that lithium be considered an essential nutrient. It may be time to take a closer look at this ancient remedy.

When you write with it, you’re scraping off a very thin layer. For decades, scientists tried to slice a layer just one atom thick—which they called graphene.

But it was only 13 years ago, at the University of Manchester, that they succeeded. Graphene turned out to be far more miraculous than they could have ever imagined.

It’s the thinnest compound known to man, thousands of times thinner than the human hair. It’s also the lightest, a thousand times less dense than paper.

Graphene is harder than diamonds, and 200 times stronger than the strongest steel. Its ability to conduct heat is 1000 times greater than copper. It’s also the best-known conductor of electricity at room temperature.

It’s impermeable to gases—not even helium can pass through it—while being transparent, highly flexible, even stretchable. And get this: if it does get torn, it can repair itself.

Not surprisingly, this incredible material will transform our lives in the future. It will lead to lighter, faster, more efficient and much smaller electronics. Lighter, stronger aircraft. New industrial products, like impermeable paint. Consumer products, like better tennis rackets. And because graphene is carbon-based, just as we are, the biotech possibilities are too many to mention.

Diamonds are transparent, prized for their clarity and brilliance. Graphite is opaque and nearly black, valued for its ability to leave marks—which is why it’s used as pencil lead.

Diamonds are famously hard. This makes them highly abrasive, and used on saw blades, drill bits, and sandpaper. Graphite is incredibly soft and is so nonabrasive that it’s commonly used as a lubricant.

Diamonds are an excellent heat conductor, while graphite can be used as an insulator.

How could two minerals from the same element be such different characters? The answers lie in where they were born and how they were formed.

Diamonds are created deep within Earth under intense heat and pressure. Their crystal structure is bonded tightly together in three dimensions. Graphite is formed from organic matter when it’s heated during continental plate collisions. Its mineral structure is in sheets, which are bonded loosely together and can slip past one another.

Different minerals made of the same element are called allotropes and are more common than you’d think. There are other natural and man-made allotropes of pure carbon. All have different characters depending on their crystal structure—and one of them will likely change our lives. We’ll talk more about it on a future EarthDate.

Of course, your smartphone is a miracle of GPS navigation. It receives data from a network of 31 satellites orbiting about 12,000 miles above us—at least 4 of them are visible from any place on Earth at any time. It uses that data to pinpoint your location to within 10 feet. Pretty amazing.

But there are many other ways that GPS impacts our lives. It helps airline pilots and ship captains stay on course. It helps taxis find their fares and military missions find their targets. And it plays important roles in bank transactions and power grids.

In fact, because the GPS satellite network is even more stable than the shifting surface of the planet, scientists now use it to track continental plate movement.

It shows that Australia moves as fast as fingernails grow, about 3 inches a year, while Hawaii holds the record, moving toward Japan at 4 inches a year.

Geodetic surveys correct GPS coordinates for the shifting earth and send updates to our devices on demand. 

And the whole thing is about to get more precise. The next generation of GPS will use both satellite and ground stations to be accurate to within 1 inch.

We’ll need it, as future technologies like driverless cars, delivery drones, and things we can’t even yet imagine, rely on GPS for increasing precision.

Well, a total eclipse happens only when the moon passes perfectly in front of the sun, blocking its view from Earth. Because the moon is so much smaller than the sun, the “path of totality,” where the sun is completely obscured, is quite narrow.

This may be easiest to imagine if you picture the view from space. You’d see a small moon shadow 70 miles wide cast upon the surface of Earth and moving across it at 1,500 miles an hour.

That moon shadow crossed the U.S. from Oregon to South Carolina, passing over 50 million people who live there—and several million more who traveled there to see it. And I was one of them.

Here’s what we saw:

The moon shadow raced forward, eventually engulfing us. Darkness fell. The temperature dropped 10 degrees. Sunset descended on all horizons. Birds stopped chirping, and night insects began.

It was an amazing, almost unnerving experience.

Then as quickly as it started, it was over, and the moon shadow raced on.

Now, if I’m making you more disappointed that you missed it, don’t be. Seven years from now, a total eclipse will return. Because of the orientation of the sun, moon, and Earth, the path of totality will be wider, and it will cross from Texas to Maine.

So set a reminder on your calendar for April 8, 2024.

The Rockies? At 3,000 miles, they traverse the U.S., Canada, and Mexico. But they’re not even close.

How about the Andes? Nope. They stretch most of the length of South America, but that’s just 4,000 miles.

The longest range in the world is over 40,000 miles long. Yes, one and a half times the circumference of the globe itself! How could that be?

Well, this range zig-zags across Earth like the stitch lines on a baseball, but there’s only one place you can easily see it: in Iceland. Everywhere else, it’s underwater.

That’s right, this mountain range follows the tectonic plate boundaries between continents, under the ocean. This chain, called the mid-ocean ridge, is created as the plates spread apart, when molten mantle pushes up to fill in the opening space. At these points you can see the ocean floor forming. Provided, that is, you have a deep-sea submersible.

At times the top of the ridge is a mile underwater. But because the ocean around it might be more than 2 miles deep, that means these mountains are still a mile high!

If you didn’t already know about this, don’t feel too bad. It wasn’t until the 1950’s that scientists had the technology to notice the largest continuous geologic feature on Earth.

Predators developed binocular vision, to give them better depth perception when hunting prey. As a response, prey developed eyes on the sides or tops of their heads, for a wide field of view to detect predators. A raptor can spot a rabbit from more than a mile away. Butterflies see ultraviolet light, to find flowers and mates. But there was a time long ago when life on Earth was blind.

Then, about 500 million years ago, trilobites evolved. Much like today’s horseshoe crabs, they scuttled around the ocean floor looking for marine worms or carrion to scavenge. And to help find food, they began to develop eyes.

This amazing new capability allowed them to spread across the globe, adapt to different environments, and diversify into as many as 20,000 species, ranging in size from a fingertip to trash-can lid.

Trilobite eyes forced other organisms to evolve defense mechanisms like locomotion and camouflage—and eyes—to compete with them for food and to avoid being eaten. Some scientists think that trilobite eyes encouraged the explosion of diverse life forms that led to the dinosaurs.

Vision enabled trilobites to dominate Earth for more than 100 million years. And although they eventually went extinct, vision has survived across the millennia.

So next time you use your eyes, thank the lowly trilobite for getting the party started.

That same summer, Mary Shelley spent a chilly vacation holed up indoors—and used the time to write Frankenstein. Crops failed around the world, plunging Thomas Jefferson into serious debt for the rest of his life. Oats became scarce in Germany, making horse travel expensive—and leading to the invention of the bicycle. Struggling farmers in China began raising opium, giving rise to a drug trade that has lasted to modern times. And famine in many areas led to widespread disease, including a cholera outbreak that killed millions.

What was the cause of all this chaos? A year earlier, a volcano erupted in Indonesia.

Larger than Krakatoa, Vesuvius, or Mount St. Helens, Mount Tambora erupted for 2 weeks straight. Around it, nearly 100,000 people died, buried under thick layers of ash like in Pompeii.

Greenhouse-gas emissions from the eruption, which could have warmed the atmosphere, were offset by particulates and sulfur dioxide gas. Ash and dust blocked out the sun temporarily, darkening skies around the world. The sulfur dioxide was longer-lasting, becoming aerosols that reflected the sun’s heat for 3 years!

This turned 1816 into “The Year Without a Summer,” as it was called, with long-term global effects. The good news? The atmosphere recovered within a decade, and life went back to normal.

Scientists have shown that gem-grade diamonds were created between 1 and 3.5 billion years ago. The diamond on your finger could be nearly as old as Earth itself.

Diamonds form deep within the planet, 100 miles down or more, underneath the continents. There, the pressure, temperature, and chemistry of the upper mantle create the perfect environment for diamonds, at 2000°F.

So how did they get to the surface? Through ancient eruptions. Jets of mantle were propelled by expanding gas, some from 400 miles within the earth—far deeper than modern-day volcanic eruptions.

The eruptions blasted through these diamond zones and carried small quantities of diamonds up with them, in shafts we now call kimberlite pipes. But less than 1% of the 6,000 pipes we’ve discovered have produced diamonds economically.

All we see of the pipes today are their carrot-shaped roots, which is where we dig our most productive diamond mines. A smaller number of diamonds erode out of the pipes and end up in streams, beaches, and undersea deposits. Offshore of Namibia, giant ships vacuum them from the seafloor.

The ancient origins of this gemstone give a whole new meaning to the phrase, “a diamond is forever.” Perhaps it’s no coincidence that diamonds have come to represent everlasting love.

Every few days, the sun emits electrically charged particles, which stream to Earth in what we call solar wind. And when solar wind meets Earth’s magnetic field, we sometimes get…a magnetic storm.

Magnetic storms can interfere with satellite, GPS, and radio signals. But their most serious effect is when they create electric fields in Earth’s interior.

These electric fields have melted power-line transformers and even caused a power grid in Canada to fail, leaving 6 million people without electricity.

Magnetic storms are more common at higher latitudes, where they create the famous Northern Lights. During intense storms, these auroras can light up the sky much farther south, into the central United States and beyond.

How much a magnetic storm could affect the power grid depends on geology. Sedimentary rocks, like sandstone and limestone, are good conductors. In areas with these types of rocks, the natural currents tend to stay in the ground.

But igneous rocks, like granite, are poor conductors. Here, electric fields look for more conductive paths, which tend to be manmade networks, like power grids—which may not be able to withstand that unpredictable extra current.

To help utility companies safeguard against these effects, scientists are combining ground-conductivity data with magnetic-storm history to produce a geoelectric hazard map.

It’s a new way of weather forecasting that just may help keep the lights on.

They learned to write. Drove your first car. Took the hand of the person you’d marry. They work every day, in an office, shop, or laboratory. And they held, or will hold, your children for the very first time.

Your hands will touch every part of your time on Earth— but the minerals that make them up are eternal.

The calcium in the bones of your hands is older than Earth itself. It formed after the Big Bang through supernova explosions and became concentrated in rocky planets.

Once on Earth, it may have spent 500 million years drifting in seawater, or passing through generations of ancient sea creatures. 200 million years more in the age of dinosaurs, making up the bones of tyrannosaurs or the eggshells of Pteranodons.

Your calcium then journeyed through 100 million years of mammals—finally pausing for a geologic split second to form your hands.

After your hands have held their last cup of coffee or played their last song, no matter how your remains are disposed of, your calcium will one day reenter the earth.

Who knows where it might end up next? Perhaps it could pass through the bones of generations of future humans. One of whom just may take a tiny part of you, once again, to another galaxy.

Recently, paleontologists discovered the fossil of a baby titanosaur from Madagascar. As an adult, this species could grow to 50 ft long. Yet their eggs were smaller than soccer balls, and their hatchlings weighed just 7 lb. How did they get from the size of a human baby to bigger than a city bus?

While the infants of many species look very different from adults, this fossil baby was almost a perfect copy. The scientists used CT scans to look inside its bones and discovered patterns of very rapid growth showing that, since hatching, it had added 10 times its weight in a matter of weeks. A study of its joints then showed it would have been much more agile than its lumbering parents.

Taken together, its adultlike proportions, rapid growth, and athleticism suggest that this little sauropod—unlike humans—would have had to fend for itself right after hatching, like many modern lizards. Its ability to find large quantities of food to be able to grow that quickly must have been key to its success.

Scientists still don’t know much about the parenting habits of dinosaurs, but this tiny titan is shedding new light.

It’s so big that it looks like a flaw in the satellite photo. But it’s actually the world’s largest deposit of lithium, which has eroded from the Andes Mountains to form an enormous salt flat.

Lithium is a very special element. It’s the lightest metal, with an atomic number of 3. Only hydrogen and helium are lighter, and they’re gases.

It’s also highly reactive, because its third electron, circling alone in an outer orbit, is eager to bond with other elements.

These two qualities, light weight and reactivity, make it perfect for rechargeable batteries.

In fact, the lithium-ion battery has changed the world. It has allowed portable computers and mobile phones to become increasingly lighter and smaller, fundamentally altering the way we work, communicate, and access information.

Continued advances in lithium batteries are expected to make electric cars cheaper and lighter, with the ability to drive longer on a single charge.

They may also lead to widespread power-grid batteries. These could provide better, more portable storage of electricity to stabilize the output of renewable energies, when the wind’s not blowing or the sun’s not shining.

This has made lithium a highly valuable commodity and could turn the Bolivian salt flat, once a remote tourist destination, into a powerful economic resource for the world.

Lucy—the 3-million-year-old skeleton of one of our oldest known human relatives—was recently on a museum tour of the United States.

During her visit, University of Texas scientists examined her skeleton with geological CT scanners, similar to medical CAT scans but with higher resolution.

Fossil bones often break as they’re buried, but Lucy’s upper arm showed something unusual. It was compressed, with sharp fracture lines and tiny bone fragments intact.

The team called in an orthopedic surgeon, who confirmed that this injury in modern humans only occurs when they extend their arms to try to break a fall from considerable height.

So they began to look for other fracture evidence of a fall—and found it, in her ankle, knee, pelvis, and ribs.

They then looked to modern chimpanzees, which are about the same size as Lucy. Chimps nest in trees at heights of up to 35 ft, high enough that a fall could result in the same type and degree of fracturing found in Lucy.

Further studies using the CT data showed that her ratio of arm strength to leg strength was more like chimps than humans.

Both findings suggest that 3 million years ago, our ancestors may have lived a significant part of their lives in the trees.

But where does the magnetic field come from?

The inner core of Earth is very, very hot—about 6,000°C, the same as the surface of the sun.

At that temperature, you’d expect it to be liquid or even gas. But because the pressure at the core is so extraordinary, about 2 million times what it is on the surface, the inner core stays solid. In fact, it’s 85 percent solid iron.

The outer core of Earth is also mostly iron, but because the pressure is lower, it’s liquid.  

As lighter elements, at different temperatures, gradually rise through the liquid iron, they cause convection currents to form, like cream swirling in your coffee. Meanwhile, Earth’s rotation causes spinning eddies to develop.

This somewhat-organized circulation of liquid metal creates electric currents, which charge Earth’s iron core, turning it into a giant electromagnet.

The magnetic field in the core is thought to be more than 10 times stronger than on the surface —and strong enough to extend 400,000 miles into space. Which is what allows it to protect us from the hazards of space.

Diamonds form deep within Earth’s mantle, of pure carbon. Their atomic bonds are so strong that they’re Earth’s hardest mineral and our best conductor of heat.

These properties make diamonds valuable for industrial purposes—like on drill bits or rock saws, or in electronics for extreme environments. But that’s not the big surprise.

A diamond’s pure carbon structure makes it very clear. But sometimes trace amounts of boron or nitrogen, the elements on either side of carbon on the periodic table, will sneak in.

Boron turns a diamond blue, like the famous Hope Diamond. Nitrogen turns it yellow. Normally, this would make a diamond less desirable.

But it’s nitrogen that could make diamonds more valuable than ever.

Scientists at the City College of New York have figured out how to activate the nitrogen with red and green lasers, allowing them to store and erase data in three dimensions along the diamond’s crystal structure, at the atomic level. Think about that.

The technology is in its early stages, but researchers believe a diamond the size of a grain of rice could store the entire Library of Congress—five hundred times.

Think about that.

In the future, diamonds could open the possibility for tiny computers or medical devices to bring a shine to our lives that we can only imagine.

The first two happened several hundred million years ago. One was caused by a major ice age; the other, by falling oxygen levels in the world’s oceans.

The next big extinction, 250 million years ago, is called the Great Dying, because 96 percent of living species were wiped out. This one, and the one that followed at 200 million years, seem to have been triggered by a hotter climate.

There are many theories about what caused them, including meteorites, major lava flows, hydrate melts, and other climate events. Probably some of each.

One thing is consistent: dying species left empty environmental niches, which surviving species could then evolve to fill. In this way, these two extinctions allowed dinosaurs to dominate Earth.

Their rule lasted 200 million years, until volcanic activity started their decline. Then, around 65 million years ago, an asteroid famously hit Earth. Ash darkened the skies and plunged Earth into global winter, triggering the last great extinction.

Dinosaurs died off, and small animals with warm blood had a huge advantage. This gave rise to the age of mammals, and some of them, millions of years later, became you and me.

In this way, each extinction made it possible for new and often more advanced life forms to replace the old ones. Without that asteroid, we wouldn’t be here.

Even more amazing is that the magnetic field is keeping us alive right now. Without it, there would be no life on Earth. We’re talking Mars.

Here’s how it works: Our magnetic field is generated in Earth’s core. It flows outward through the crust and surrounds Earth like a giant bubble, called the magnetosphere, which extends more than 400,000 miles into space. But on the side that faces the sun, solar winds squash it down to just 40,000 miles.

It’s the force of that magnetic field, pushing back against the solar winds, that keeps them from scouring away Earth’s atmosphere. 

Scientists even think that, billions of years ago when Earth was forming, our magnetic field helped trap the gases that made up our atmosphere in the first place.

By contrast, when a planet loses its magnetic field, its atmosphere declines with it, like we see on Mars.

Magnetic field means atmosphere means life on Earth. That’s pretty mind-blowing!

So the next time you see a compass, take a moment to remind yourself that our lives are made possible because we’re living on a giant magnet.

Most of us remember the news footage from those grim days. What you may not remember is that the tsunami was caused by an earthquake. Scientists now know it was the most powerful earthquake in 40 years, a 9.3 on the Richter scale. Its epicenter was below the ocean floor, about 100 miles west of Sumatra.

The quake had the longest duration ever recorded, about 10 minutes of continuous motion as Earth’s crust ripped to form a 50-foot cliff on the seafloor. The tear continued moving north for almost an hour, finally extending more than 750 miles.

It was the huge volume of water displaced by this movement that caused the tsunami.

The quake shook the ground everywhere on Earth and triggered powerful aftershocks and earthquakes as far away as Alaska. The entire planet vibrated for weeks.

GPS data showed changes in the surface of most of the Eastern Hemisphere. Masses inside Earth shifted, which moved the location of the North Pole by an inch. Even the shape of the globe changed—very slightly, but enough to increase its rotational speed and shorten the length of the day by 3 microseconds.

December 26, 2004, was a shocking day in Earth’s history, for humans and the planet itself.

Now imagine 12 of them lined up on a table. That’s how much water the average American is carrying inside their body. 12 gallons. That’s a lot of water!

Every day we’re exhaling water vapor, sweating or excreting water, and if we don’t drink water or eat watery foods to replenish it, in as few as 3 days we’d be dead.

Water is very much a life or death issue to all humans and all living creatures. But for the most part, we take it for granted. Often when that happens, it’s because we have an abundance of something.

But do we? Sure, we live on the Blue Planet. Look at a photo taken from space and it’s easy to see that 70 percent of Earth is covered in water.

Take a closer look, though, and you’ll see that number is misleading. Water, even groundwater, is really just on the surface of Earth. Oceans may seem deep to us, but they’re incredibly shallow, just a sliver-thin veneer compared to the massive diameter of Earth.

As a matter of fact, all the water on the entire planet would fit into a sphere the width of Texas. And the fresh water that we depend on is less than 1 percent of that.

Fresh water is indeed a precious resource—and a topic you’ll hear a lot more about, on EarthDate.