Episodes

Horses changed human history. But first we had to change horses. The horse evolved in North America 50 million years ago, and migrated across the Bering land bridge into Eurasia. Then, during the last Ice Age, it went extinct in the Americas. Around 5,000 years ago, humans began taming horses in the Eurasian Steppe, in what is today Kazakhstan, Russia and Ukraine. There, archaeologists have found residue of mare’s milk in drinking vessels. Some horse skeletons show wear on their teeth suggest...

Famous early scientists, like Leonardo da Vinci, would not have called themselves scientists, or practiced science as we do today. They were then more commonly called ‘natural philosophers,’ and based their work on observing the natural world, then inferring principles. Until Sir Isaac Newton, and his colleague Sir Francis Bacon, moved to standardize the scientific method. They wanted proof; knowledge based on evidence, not speculation. So they argued that scientists should put forth a hypot...

Two hundred million years ago, the ginkgo tree evolved to be very stinky, because there was a creature that loved it. The ginkgo is unlike any other tree; not a conifer, not a flowering deciduous. When pollen from the male ginkgo fertilizes an ovule of the female, it produces a round yellow fruit full of butyric acid, which smells -- especially when it falls and rots on the ground – like, well, vomit. But there must have been a dinosaur or other creature that found this smell appetizing. So i...

The Chernobyl nuclear powerplant, in Ukraine, was designed and operated so badly, it was practically destined for disaster. First, the Soviet plant design was fatally flawed. It didn’t include a containment vessel, the massive concrete structure that encloses other nuclear reactors. Adding one, of course, would have been very expensive. But, it would have contained the accident. It occurred when unqualified engineers ran the reactor at very low power during a test – which made the reaction uns...

Just eight percent of Earth’s surface is covered in topsoil -- but that grows 95 percent of our crops. And healthy plant growth depends on healthy soil. Which depends on a healthy population of soil life. As noted in an earlier EarthDate, a single handful of healthy soil contains more microbes than the human population of Earth. And more biodiversity than the entire Amazon. One handful. Along with microbes, there are fungi, worms, insects, plant roots, and much more. And they all make noise....

In 2024, Spanish oceanographers studying the deep seafloor west of the Canary Islands discovered an enormous seamount -- A mile-high, 70-mile long mountain on the bottom of the ocean, formed of three inter-linked ancient volcanoes. At its summit, just 200 feet beneath the water’s surface, they found sand dunes and cliff faces that could only have been formed if it had once been above water. During the last Ice Age, when Earth’s water was locked up in continental ice sheets, sea level was over...

There are many kinds of floods. River floods develop slowly, water gradually rising over days, providing ample time to evacuate. Coastal floods come mostly from storm surges, when a hurricane or tsunami makes landfall. Coastal communities also have evacuation warnings. But when not, these can be catastrophic. Urban flooding happens increasingly as paved areas expand, preventing the land from absorbing rainfall. Flash floods, though often localized, can be the deadliest for their size, simpl...

Greenhouse gases trap heat in the atmosphere and keep Earth warm. Without them it would be a frozen iceball – as it once was before. There are many greenhouse gases. Water vapor is by far the largest by volume, and does most of the warming. Carbon dioxide is the weakest greenhouse gas in warming potential, but the second most abundant. Carbon is always moving between Earth and sky in what’s called the carbon cycle. But since humans have industrialized, we’re transferring carbon that was held...

Billions of years ago, the globe spun twice as fast as today; a complete rotation took just 6 hours. Then Earth’s rotation slowed, and that’s why you’re here listening to this episode. Let me explain. The atmosphere of early Earth was made up of methane, CO2 and sulfur gases. But no oxygen. Eventually, as noted on a prior EarthDate, cyanobacteria, blue-green algae, began to produce oxygen through photosynthesis. At first, the amount of oxygen they released was so small that it was absorbed b...

Each year, U.S. drivers collide with 1 to 2 million large animals, often killing them and endangering the drivers. Add in smaller creatures, and studies estimate up to 300 million animals die on U.S. roads annually. An astounding number. This is because wildlife must roam, and always has -- to find food and water, breed and raise young, and migrate seasonally. They often follow ecological corridors dictated by geography and natural resources. These pathways could be millennia old. But in the...

Sand dunes are dynamic, always changing. They occur wherever there’s sand, even thousands of miles from the sea. Even on the shores of freshwater lakes. And the largest freshwater dunes in the world, more than 400 feet high, are in Michigan, on the shores of the Great Lakes. They’re made of sand formed during the last Ice Age. Continental glaciers ground up rock as they moved, and deposited sand in the basins that would become the Great Lakes. Dunes form here, like everywhere, when wind pic...

Around the world, a small group of secluded libraries contain some of the rarest and most fragile objects on Earth. They’re staffed by scientists, equipped with redundant power supplies… and kept very, very cold. That’s because the ‘books’ in these libraries are ice cores. They’re collected in some of Earth’s harshest environments, like Antarctica and Greenland, at great cost, then transported frozen to these libraries. Each core is one of a kind. And once it’s been read – small samples melt...

In 1984, an engineer walked into a nuclear power plant under construction and set off radiation alarms. But there was no nuclear material yet on site. Where was the radiation coming from? Testing revealed the man was carrying it, on his clothes. Where did he become so contaminated? Turns out, at home. Scientists visited his house and found levels of radon gas 600 times higher than normal – the highest level ever measured inside a building. They immediately moved the man and his family out. ...

We often think of rivers as mostly straight or gently bending waterways. If they are, it’s because we’ve made them that way, guiding them with levees or dredging them for navigation. When viewed from the air, natural rivers, especially across nearly flat landscapes, bend dramatically, sometimes folding back on themselves. Rivers meander, constantly changing their paths. Rivers have several sources: lakes, springs, drainage plains, and melting snow or glaciers. When they originate in steep a...

Five centuries ago, the last emperor of the Aztecs drank a full gallon each day of a coveted beverage, rich in vitamins and caffeine. The Aztec word for it: xocolatl Chocolate. Just like today’s chocolate drinks, his was made from the ground seeds of the cacao fruit. The Olmecs and Mayans before him domesticated the cacao, an understory tree from Ecuador. There and in Mexico, it thrived – under very specific conditions: Steady warm temperatures. Abundant rainfall. Well drained volcanic soil...

Volcanoes often form where tectonic plates collide or pull apart. But sometimes they’ll form in the middle of plates, due to geologic hotspots. A hotspot is a plume of hot mantle that rises from within Earth, and heats, expands and deforms the crust above it, to create mountains, volcanoes or volcanic islands. The classic example is the chain of Hawaiian Islands, which formed as the Pacific plate traveled across a hotspot. Scientists always thought hotspots were stationary, while tectonic pla...

Geothermal energy, the heat of the earth, can be found under our feet everywhere on Earth. Historically, we’ve only been able to access it in a few places, commonly in hot springs. Much less commonly, in far fewer places, we find more intense heat, so close to the surface that it can be used to heat cities or generate electricity. That intense heat could be developed anywhere… if we could go deep enough, cheaply enough. And that’s always been the challenge: How to reach it, how to bring it b...

Humans have lost most of our body hair, but the beard has stubbornly remained – though anthropologists can find no function for it. Perhaps that’s why men have been grooming it, or removing it, for thousands of years. Early cave paintings show men with smooth faces. Archeologists have found flint ‘razors’ they may have used to shave. And shell ‘tweezers’ they may have used to pluck off their beards. Ouch! The Egyptians were first to engage in elaborate shaving rituals. Facial hair was consi...

Birds have very large brains for their body size. New research is helping scientists understand how they work, and came to be. One part of a bird’s brain, the cerebellum, controls their amazing flight capabilities – their spatial awareness, allowing sudden direction changes through tree branches, or their ability to chart migration over thousands of miles. PET scans taken pre- and post-flight have shown very high brain activity in the cerebellum, especially the neural pathways connected to the...

If you believe the old cartoons, elephants are afraid of mice. But would a woolly mammoth be afraid of a woolly mouse? We may soon find out. That’s because scientists have recently used gene editing tools to tweak the mouse genetic code, adding genes from woolly mammoth DNA. The result? The woolly mouse, with long, shaggy fur and extra insulating fat. Fortunately, no tusks. The woolly mouse is the first step toward the de-extinction of the woolly mammoth itself. For that, the scientists will...

Rare Earth Elements, or REEs, are a group of 17 trace metals that play important roles in the electronics we rely on daily. Their properties are so unique, they’re not replaceable. But their current supply is almost completely controlled by China, which creates shortages and security challenges. So, researchers are looking for domestic sources—and have found a surprising one: coal ash. When coal is burned at a power plant, it’s reduced to gases and about 10 percent of its weight in ash. In tha...

You may remember that opposite electrical charges attract. If a positive charge builds up, it seeks to connect to a negative charge, to reach equilibrium. This is what creates lightning. As explained in a prior episode, it’s generated by the static electricity of water vapor and ice molecules rubbing against each other. Billions and billions of molecules can produce a whopping charge. Positive and negative charges build within the cloud, but they’re separated by air, which is a poor conductor...

You may have heard that hydrogen could be a fuel of the future, with lower carbon emissions than any we’re using today. When it’s burned, it produces only water vapor and a lot of useful energy as heat. That sounds pretty good. And hydrogen is the most abundant element in the universe. That sounds good too. But nearly all hydrogen on Earth is bound up in other compounds, like water. Or natural gas—methane—which is one carbon atom and four hydrogens. Today, we get most of our hydrogen by spli...

On the east coast of the Yucatan Peninsula lie the wetlands of Belize. Swampy, hot and full of mosquitoes, these are unappealing places. But when they dry out each season, visitors noticed earthen banks that cut across the marsh. They thought these were water gathering facilities created by the Maya, who populated Belize centuries ago. Then carbon dating revealed they were at least a thousand years older. What could they be? When extended drought dried the swamps long enough for detailed fie...