Episodes

If you live in or visit the mountains, you can look at the snow-covered hills as nature’s water towers. As that snow melts, it could provide 75 percent or more of the area’s freshwater each year. That’s true far downstream from the mountains too, and even in snowy flat areas. Around the world, snow provides 50 percent of our total annual freshwater supply. And it does more than that: snow reflects sunlight, keeping areas cooler and making it possible for snow to accumulate. Snow protects against...

In another episode, we talked about the horseshoe crab, which has existed on Earth nearly unchanged for more than 400 million years. In the last 40 years, it’s become a vital player in our medical industry. Why? It’s in their blood. Horseshoe crab blood is copper based, not iron based like ours, which makes it blue. It coagulates so rapidly and completely around invading pathogens, that medical researchers realized it could be used to detect pathogens for us too. So they isolated the coagulating...

You might have heard of your microbiome, but did you know you also have a virome? That’s right, there are more than a trillion active viruses within you right now. Viruses exist in every organism, in every environment. There are at least ten times more viruses on Earth than all other biological entities combined. A virus is a tiny packet of RNA or DNA, about 1500 times smaller than a grain of salt. They lack the ability to reproduce or the ribosomes to make energy. Many scientists don’t even con...

To Egyptians and ancient Greeks, amethysts were as precious as diamonds, rubies, and sapphires. The stone was thought to cool tempers and prevent drunkenness, so it was cut into jewelry for wise kings and crafted into wine goblets for those who hoped to stay sober. In the Middle Ages, it adorned the rings of religious leaders and the scepters of royalty. Since then, huge finds in many places, especially Brazil and Uruguay, have made amethyst plentiful and affordable. And that’s good, because thi...

Dr. Gene Shoemaker mapped the moon, trained astronauts and discovered more than 800 asteroids. He was also the first person to go to the moon… and stay there. Shoemaker started his career with a bang, proving with his Princeton dissertation that the mile-wide Barringer Crater in Arizona, previously attributed to volcanic activity, was in fact the result of a meteorite impact. Soon after, he founded the astrogeology program of the U.S. Geological Survey, in part to better understand the potential...

When scientists mapped the human genome, they found that just 2% of it controlled our own functioning. Fully 8% was the DNA of fossil viruses. Paleovirologists who study fossil viruses have found that all viruses share a common single-cell ancestor from more than 3 billion years ago. About 1.5 billion years ago, viruses changed their protein coating, allowing them to penetrate the cells of their hosts. As multicellular life became increasingly complex, viruses got simpler, eventually giving up i...

In earlier episodes, you heard that trillions of viruses live peacefully, even beneficially, within each of us today. And that our ancestors battled now-extinct “fossil viruses,” which are preserved in our own genetic code. Turns out, that’s been beneficial too. For instance, viruses helped drive our evolution. 100 million years ago, proto-mammals were infected with a virus that encoded into their DNA the ability to produce syncytin, a protein that viruses use to fuse cells together so they can ...

Mt. Everest, at just over 29,000 feet above sea level, may be the highest point on Earth’s surface—but what’s the lowest? Well, the deepest part of the deep sea is the Mariana Trench in the Pacific, off the island of Guam, about halfway between Japan and Australia. It’s five times as long as the Grand Canyon and more than a mile deeper than Everest is tall. And the deepest point in the trench is called Challenger Deep, nearly 36,000 feet below sea level. It’s named after the Challenger 1 and 2 e...

In another EarthDate, we talked about Challenger Deep, the deepest point in all the oceans, at almost 7 miles down. The first humans to explore it were a Swiss oceanographer and U.S. Navy Lieutenant. They built a special deepwater submarine called a bathyscaphe, and in 1960, headed for the bottom. It took them 3 hours to reach the western pool of Challenger Deep at 35,000 feet. But they stirred up so much sediment, they couldn’t see anything. That, and a worrisome crack in a window, cut their tr...

You may have heard that bumblebees shouldn’t be able to fly. That’s a myth actually, as any flying bumblebee will tell you. The science of their flight is now understood. But the bees hold another mystery that could affect human agriculture. Bumblebees hibernate over winter, and when they emerge in the spring, they’re hungry. But what if the plants they rely on for pollen and nectar aren’t yet producing? The bees actually force them to do it. Like their honeybee cousins, bumblebees scout their e...

What if you’re a fish in freezing water? Well, a free-swimming ocean fish can migrate to a warmer part of the sea. But if you’re a lake fish, you don’t have that option. Luckily, the properties of water make its solid form—ice—less dense than its liquid form. As a lake freezes, the ice floats on the surface, insulating the water below and keeping most lakes—and the fish within them—from freezing solid. You would still, however, be very cold. Lake fish have to lower their metabolism and enter a s...

The horseshoe crab is a living fossil—sometimes called a stabilomorph, a body design that evolution got so right, it hasn’t had to change. They’ve been roaming the coastal shelves and brackish bays of Earth for more than 400 million years in nearly the identical form as today, having survived all five great extinction events we’ve discussed on EarthDate—including the asteroid that wiped out the dinosaurs. Why are they so enduring? A few reasons: They’re generalists that can live in shallow or de...

How long is a second? That depends on how you measure it. In a previous EarthDate, we talked about how people divided the day into 24 hours, then hours and minutes into 60. That made the second 1/86,400th of a day. But how long is a day? Turns out, that’s not constant. Earth wobbles slightly on its axis, changing its rotation time. So scientists settled on a year, reasoning the day’s length would average out. But which year? Those aren’t constant either. So they agreed on a specific year: 1900. ...

Each winter in the Northern Hemisphere, it feels like Earth is drifting farther away from the warmth of the Sun. In fact, it’s just the opposite. When we measure the size of the Sun in our sky, we find that it actually appears 3.4% larger in winter—because it’s 3.4% closer. More than 3 million miles closer. The Sun is about 95 million miles away in summer, but just 92 million in winter. And this is because Earth’s orbit is elliptical, with Earth following the closer part of its path during the n...

You’ve probably heard that no two snowflakes are alike. And mostly, that’s true. Snowflakes aren’t formed from freezing water, but when water vapor freezes, skipping the liquid stage altogether. This allows the water molecules to organize themselves into the snowflake’s delicate structure. Snow crystals come in more than 30 basic shapes, with the classic star-shaped snowflake forming best in temperatures around 5 degrees Fahrenheit. These begin when water vapor freezes around a nucleus like a du...

The waterfall. In concept, it’s simple: just water… falling. But in life, waterfalls are a wonder. Beautiful, frightening, powerful, calming, deafening, soothing—sometimes all at once. They’ve been inspiring humans for millennia. When water flows over a wide shelf, it’s called a block falls. The widest is Victoria Falls in Zambia, over one mile across. Called “smoke that thunders” in the local language, it can be heard 25 miles away. Human tools have been found there from 50,000 years ago. The t...

We have 10 fingers, so we’ve based our common counting systems on 10. Why then, do we divide the day into 12 hours and the hour into 60 minutes? To understand, we need to go back 3000 years. Babylonians also used their hands to count, but wanting to count higher than 10, they devised a different system. They used their thumb to count the three segments of their four fingers to get 12. They marked that 12 by raising a finger on the other hand. Twelve times five fingers is 60. 2500 years ago, when...

Imagine walking down a beautiful tropical beach. You spot a fruit on the sand, like a plum or small ripe apple. It smells sweet, so you wash it in the water and you’re about to take a bite… But wait! You may have in your hand a Death Apple, the fruit of the manchineel, a tree that’s relatively common to the tropical beaches of the Americas. Despite its good looks, the manchineel is listed in the Guinness Book of Records as the most dangerous tree in the world. Every part of it is highly toxic. T...

Earth has experienced dozens of ice ages in the past few million years. At the coldest point of the most recent one, ice sheets over a thousand feet thick covered much of North America. Then, 15,000 years ago, the world began to warm, and ice started melting—until 13,000 years ago, when Earth plunged back into the Ice Age for a thousand more years. Scientists thought this may have been caused by trillions of gallons of cold glacial meltwater flooding out into oceans, interrupting the warmer surf...

Greenland is Earth’s largest island, and most of it is covered by ice up to 2 miles thick. Scientists decided to investigate the age of this ice sheet and were surprised to find that not that long ago, there wasn’t one. They used ice cores to date different areas, then flew planes over it with special ice-penetrating radar. The radar identified bands of softer and harder ice and layers within them, which they matched to the ice cores to determine different ages of ice across the island. Turns ou...

X-rays are common today, but their accidental discovery 125 years ago was celebrated around the world as a scientific miracle and earned Wilhelm Röntgen the first Nobel Prize in physics. Röntgen was working in his lab in Germany, trying to replicate the experiments of other scientists with an electrified cathode tube, when he noticed some barium-painted cardboard nearby fluorescing. Puzzled, he turned off the lights, but it continued to glow. He realized the cathode tube was emitting something o...

In a previous EarthDate, we told you about the accidental discovery of X-rays in the late 1800s. Scientists around the world began to experiment with them. Thinking them no more harmful than visible light, they did so without protection… sometimes with disastrous results. Early researchers would place the emitter in the center of the room, hold up their hands, and—using special lenses to examine their bones—looking directly into the beam. One of Edison’s scientists absorbed enough X-rays to deve...

Earlier, you heard how geckos have a sticky superpower. Microscopic hairs on their toes generate electromagnetic attraction to the surfaces they walk on, letting them run up glass and across ceilings. Anoles—common garden lizards in the southern U.S.—have less stick. They can dash up trees but can’t cling to the underside of things. Their electromagnetic attraction evolved separately from geckos’. In fact, they diverged on their family tree more than 200 million years ago, before either develope...

They may not go into polling booths and come out with an ‘I Voted’ sticker. But most animals that live in groups have developed ways to make collective decisions and act together for the good of one and all. English rock ants are always scouting for a new nest. When a few individuals find the same new spot, they seem to agree that this real estate has potential. So they go back to the current nest to try to lead other ants over, one by one. If they can persuade enough to follow, they’ll hit a cr...