Episodes

Sometimes we have too much electricity. But more often, grid operators are carefully managing its production to be sure that we have enough. 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...

What exactly is fossil water? And why have we consumed so much of it? 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 2...

A decade ago, there were typically 20 earthquakes a year that were large enough to feel in the central and eastern U.S. But in 2015, there were over 1,000 of them. 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 w...

Shortly after modern humans arrived in Europe, the Neanderthals disappeared. And scientists think we had something to do with it. 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...

Since the dawn of humankind, people have used caves—to explore, hold religious ceremonies, create art, or avoid the dangers of weather and predators. Partly because of that, they continue to fascinate scientists today. 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 p...

Trapped beneath the permafrost, and under the deep ocean floor that surrounds continents, is enough natural gas to power humankind for thousands of years. 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...

For the majority of Earth’s history, the planet has been hotter than 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. ...

On another EarthDate, we talked about Greenhouse and Icehouse periods in Earth’s history that last hundreds of millions of years. In Greenhouse times, temperatures rise and life flourishes. And in Icehouse periods, temperatures fall and life can struggle. 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 ...

Whales and dolphins are spectacular creatures. 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 flu...

You may remember the film Close Encounters of the Third Kind, when Richard Dreyfuss fills his living room with dirt and garbage to sculpt a replica of Devils Tower. Later in the movie, the tower becomes the landing platform for alien spaceships. 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 g...

The Kingdom of Egypt prospered for 3,000 years—in the desert. Its success depended on strong leadership, written language, mathematics and engineering… but most importantly, on the flooding of the Nile, which happened each June through September. 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 rece...

Insects first appeared around 400 million years ago, long before mammals or flowering plants. Even before dinosaurs. 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 t...

It may surprise you to know that the garbage that leaves your house will be preserved for centuries—in a landfill. More than a dump, landfills are an engineered storage system. 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 close...

On other EarthDates, we talked about how humans have used, and sometimes overused, water from aquifers—to grow crops or build cities where previously none could exist. 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...

In 79 AD, 20,000 Romans lived in the town of Pompeii, near present-day Naples. Many were farmers, working the fertile soil that, unbeknownst to them, came from previous eruptions of nearby Mount Vesuvius. 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 wer...

Previously we talked about how early humans outcompeted Neanderthals. One big reason for their success might be sitting right next to you. I’m talking about dogs. 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...

Scientists studying the jet stream over Europe discovered that it has contributed to the extreme weather seen across the continent in the last 50 years. 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...

Sixty-six million years ago, three-fourths of all species on Earth died out. Scientists knew it. But they didn’t know why. 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 l...

Previously, we talked about how scientists discovered the asteroid that brought down the dinosaurs. 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 reb...

Previously, we talked about how scientists discovered the asteroid that brought down the dinosaurs. 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 reb...

Alchemists in the Middle Ages were fixated on turning lead into gold. 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 comm...

Today you can take a train, in a tunnel beneath the English Channel called the Chunnel, from London to Paris in 2 hours. 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 June, a man climbed into the Ötzal Alps, on today’s Austrian–Italian border. 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...

Though our electricity system is highly complex, its basic principle is simple: 99 percent of our electricity comes from turning a generator. 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 s...