Episodes

At midnight, at the end of the year, Earth celebrates the completion of two cycles. 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 ...

There are over 1 million avalanches every year, but they kill only 150 people. 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 side...

Maybe only Santa’s reindeer can fly—but regular reindeer come pretty close. 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 b...

There are hundreds of thousands of species of beetle, but only one species of human, and koala, and aardvark. 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...

On another episode, we talked about species that are the last of their family tree. Well, here’s one that’s the last in its genus, in its family, even in its order. 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, b...

Geothermal energy comes in three varieties. 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 geotherm...

Space is black—so why is the sky blue…and the sunset red? 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 shorte...

To make it through winter, trees have developed two very different strategies. 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...

In other EarthDates, we’ve talked about how water can shape Earth’s surface. 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...

In the 1970s, engineers drilled a series of wells off the U.S. Atlantic Coast, looking for oil. Instead they found water. Fresh water. 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 fou...

Within a tiny salmon egg, molecules of magnetite are already gathering. 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...

Think of Earth as a rubber ball. If you push in at one place, the surface will indent. Surrounding that indentation, the ball will bulge outward. 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 ...

You may remember from an earlier EarthDate that seawater is so salty, drinking it pulls water from the rest of your body, which can lead to dehydration and even death. 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 wat...

The sun may appear constant but, like most things in the universe, it’s constantly in flux—cycling between an active state, called a solar maximum, and a more restful one, called a solar minimum. 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. Cha...

What makes leaves change colors so dramatically in the fall? 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...

Earlier on EarthDate, we talked about the three North Poles. 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 navigat...

The human body is amazingly capable…despite the fact that, in many places, it’s engineered all wrong. 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 ...

The most abundant element, making up an incredible 75 percent of the known mass of the universe, is hydrogen. It also might be the energy fuel of the future. 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...

It might surprise you to know there are actually three North Poles: the geographic, the magnetic, and the geomagnetic. 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, ...

The Grand Canyon is so grand it can be seen from space. At more than a mile deep and nearly 300 miles long, it could hold all the world’s river water and still be only half full. 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, va...

Since the Roman Empire, troops have used homing pigeons to carry messages from the front lines to command posts. They remained popular for long-distance communication, even after the telegraph was invented in 1844. 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 a...

Earth is mostly covered with water, and most of that is ocean. Only 2.5 percent is fresh water. 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 ...

In October 1964, three young thieves cased the American Museum of Natural History in New York City. 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 sap...

If you’ve been to Iceland, you know it doesn’t have much ice. In fact, there’s so much grass that on maps it’s colored green. 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 die...