Episodes

Today, emeralds may be a bit less famous than their red, white, and blue cousins—diamonds, rubies, and sapphires. But they were once perhaps the most celebrated gemstone. 3,500 years ago, the Egyptians found emerald deposits in their kingdom. They ascribed to the stones many mystical properties. They were symbols of fertility and immortality, perhaps because of their “ever green” color. They were thought to increase eloquence and intuition. Some even thought they could cure malaria. Those who pu...

Machu Picchu, the Incan city built on a jagged mountain peak, is so remote that the Spanish conquistadors never found it. It’s difficult to get to, even today. We’ve long wondered why the Inca built it there. New research suggests they chose the site because it’s on the intersection of fault lines. That would seem like a terrible place to build any city! But the Inca had good reasons. The faults would have fractured the rocks there, making it easier for the Inca to dig and build flat terraces on...

If you’ve ever walked through an aspen grove, you’ve seen hundreds or thousands of white trunks propping up a sky of silvery green leaves trembling in the wind. In the fall, all the leaves in one grove will go from green to gold at the same time. This is because the entire grove is really just one organism, a massive root system from which many trunks sprout, grow, die, and are replaced by new trunks. The largest aspen grove in the world, in Utah, is named Pando: Latin for “I spread out.” It spr...

When you see white, you’re actually seeing all the visible colors of light at once. And when you see black, the object you’re looking at is absorbing light. White and black aren’t colors; they’re visual experiences. And a few rare animals can produce the visual experience of super-black. Most black surfaces are still slightly reflective. But these creatures have developed plumage or cells that absorb nearly all visible light. The male birds of paradise in Papua New Guinea have super-black feathe...

On a previous EarthDate we talked about GPS, the Global Positioning System, and recent improvements that allow mapping down to the millimeter—accurate enough to detect the creeping movement of Earth’s tectonic plates. These advances have inspired scientists to use GPS in many new ways to better understand earthquakes and other Earth processes. The signals from GPS are very long—many thousands of digits—making them too slow to track seismic activity. But recently, scientists realized they could u...

North America’s Great Lakes are great indeed. They contain 20 percent of the planet’s surface freshwater—enough to cover the continental U.S. 10 feet deep. They formed at the end of the last Ice Age, when Canada was under an ice sheet 3,000 to 9,000 feet thick. This massively heavy continental glacier had flowed southward, depressing and carving the Earth as it passed over, pushing ahead of it huge piles of eroded rock and gravel called glacial moraines. 20,000 years ago, the ice sheet finally b...

In previous episodes, we’ve talked about geothermal energy—the heat of the earth. Where extreme heat is near the surface, it can be used to produce steam to drive electric generators. Where this heat warms groundwater, it makes hot springs. But there’s another type of geothermal energy that’s more widely available: not extreme heat, but constant, low-temperature heat. Anywhere in temperate latitudes, if you dig 10 feet or more below the surface, the ground is a near-constant mild temperature all...

In two earlier episodes, we talked about the greatest environmental disaster in U.S. history: the Dust Bowl, which killed thousands and left millions homeless. 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 establish...

We often think that Thomas Edison invented the light bulb. 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 f...

Plains Indians depended on buffalo for everything: meat for food, hide for clothing, horns and bones for weapons and tools. 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 dia...

The greatest environmental disaster in American history lasted for eight years and displaced more than 3 million people. What was it? 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 Am...

Earlier, we talked about the run-up to the greatest natural disaster in American history, the Dust Bowl. 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 ...

Deep within our planet, intense heat left over from Earth’s formation is stoked by the continued decay of radioactive isotopes. 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 furth...

You may have heard that monarch butterflies migrate from Mexico to Canada and back. 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 th...

We call Earth the Blue Planet because it’s covered in water—but what makes water blue? And why is it not blue in your glass or your ice cubes? 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 t...

California is well known for droughts. But it also had one of the greatest floods in U.S. history. 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, sa...

Previously, we talked about California’s 1861 super flood that turned its Central Valley into an inland sea. 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 somethin...

The pangolin is one of the world’s most unusual animals—and one of the most heavily poached. 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. The...

Recently, a group of sailors in the South Pacific encountered something extraordinary. One minute they were sailing in water. The next, in a sea of rocks. 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 ins...

Human life has always depended on salt. Chemically, and culturally. 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...

Mass extinctions have happened throughout Earth’s history, sometimes wiping out the large majority of all life on Earth. 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 mi...

Opinions are divided on eucalyptus trees. In some places, they’re a fast-growing cash crop. In others, they’re an invasive species. 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 ...

Getting caught in quicksand can be fatal, with victims dying mostly from dehydration, hypothermia or heat exhaustion. 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...

Each year, millions of pebble-sized meteors strike Earth’s atmosphere and burn up harmlessly. 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 airb...