EarthDate

Why do zebras have stripes? It’s probably a combination of things. Zebras’ main predators are lions. Black and white stripes actually make zebras stand out against their grassland home, rather than camouflage them. But when many zebras are running simultaneously, the cacophony of stripes may confuse predators as to how many zebras there are and which way they’re moving, making it more difficult to...

Ernest Hemingway made Mount Kilimanjaro famous with his story “The Snows of Kilimanjaro”—though he never climbed the peak. But many others have. More than 30,000 try each year, with two-thirds reaching the top. Kili, as it’s called, is the tallest mountain in Africa but the easiest climb of the Seven Summits—the highest peaks on the seven continents. Its high camps have hosted some world record sp...

Have you ever seen the brilliant hues of petrified wood and wondered how it gets its colors? When trees die, they typically fall to the forest floor, where they decay. But if they fall in a place without oxygen—in water, a swamp or bog, or are buried by volcanic ash or flood silt—they may not decay. After thousands or millions of years, water seeps into the pores of the wood, carrying dissolved si...

The megalodon, Earth’s largest shark, is thankfully...extinct. It was twice the length of a school bus. Larger than most of today’s whales and three times the size of the biggest great white shark—with up to 10 times the bite force. Its jaws were filled with hundreds of six-inch teeth, which fell out and were replaced every few weeks. The megalodon’s large range meant that fossilized teeth have be...

Utah’s Great Salt Lake may seem like a wasteland, ringed by toxic deposits of mercury and arsenic, and filled with water so salty that only brine shrimp can live in it. However, those shrimp feed 10 million migrating birds. And the lake provides eight thousand jobs and two billion dollars in industry, harvesting salt and other minerals. It’s vital to the region’s ecology and economy. But the lake...

So-called water spiders aren’t spiders at all but insects specially evolved to walk on water.  There are 1,700 species of these water striders, which have existed on Earth for millions of years.  If you’ve ever wondered how they skate so effortlessly across a pond without falling in, the answer is surface tension—and their very specific adaptation to it. Water molecules, as we’ve discussed on prio...

When a thunderstorm forms over the desert, it may not produce rain—but could form a deadly dust blizzard called a haboob. When rain droplets condense within a thunderhead, they cool the air, which rushes toward Earth with the rain. If this happens over a desert, the rain will often evaporate before reaching Earth. The evaporative cooling further chills the air, which falls faster. Eventually the c...

Hail is created when rain starts falling up. This usually happens in the spring, in middle latitudes, when tall clouds form over warm updrafts. In the cold upper reaches of the cloud, water condenses around nuclei, like dust particles, dirt, or salt crystals, to form droplets of rain that begin to fall to Earth...but then are pushed back upwards by the updraft. The rain droplets tumble within the...

Giraffes are fascinating animals. They have the same number of vertebrae in their necks as humans do—seven—but each one is nearly a foot long. They have long, purple tongues too—nearly two feet—that can grasp things as easily as a monkey’s tail can, which they use to pull leaves and fruits from high branches. All four giraffe species are covered in spots. And each individual’s spots are as unique...

At the bottom of the ocean lies a treasure. But recovering it could be technically difficult, geopolitically challenging, and environmentally damaging. Eighty three percent of the ocean is a mile deep, or much more, making the deep ocean the largest environment on Earth, covering 115 million square miles. Down there, like in the Amazon, species diversity is high. There may be thousands of species...

Beavers are amazing rodents. They have long teeth that never stop growing; they control their length by gnawing on wood. They have fat-insulated bodies, webbed feet, and a large flat tail—which make them clumsy and exposed on land but quick and graceful in the water. Most importantly, beavers cut down trees to dam streams and rivers to make their homes. To many humans, these activities seem destru...

Since the peak of the last Ice Age, Earth’s ice has been melting, and sea level has risen nearly 400 feet! But only recently do we have the technology to carefully measure it. For the last 20 years, a network of satellites and nearly 4,000 robotic floats have been measuring temperature and surface elevation of the global oceans. They’ve found that the surface of the ocean has warmed an average of...

The gleaming White Cliffs of Dover have dark seams of flint within them that were the target of some of Britain’s first mines—more than six thousand years ago. The white cliffs are made of nearly pure chalk, the remains of phytoplankton, tiny floating algae. These phytoplankton lived here in warm Cretaceous seas. When they died, their spherical bodies fell apart into the hard plates that covered t...

When you watch waves crash on the beach, you’re seeing the visible end result of many invisible forces. Waves are formed near or very far from shore, usually by wind—the first invisible force. As wind blows over the sea, surface friction transfers its energy to the water. How fast, how far, and for how long the wind blows determines how much waves grow. When the wind stops blowing, the waves stop...

In the 1700’s, there was no standard of measurement. Every village had its own unit. By some estimates, there were 250,000 different units in France alone. This made commerce and mapmaking so difficult that the French government created a special bureau to standardize things. And they decided to create the meter—which they defined as one ten-millionth the distance from the equator to the North Pol...

When dinosaurs were first discovered, scientists thought they must have been cold-blooded like the lizards they resembled. Later, they realized that some dinosaurs are related to modern birds—which have the highest metabolic rate in the animal kingdom. Could dinosaurs, too, have been warm-blooded? New research reveals the answer is: both. So-called “cold-blooded” creatures, or ectotherms, are conf...

Carlsbad Caverns National Park is a very rare place. Its main room is the largest cave chamber in North America, covering more than eight acres. And its cave formations are unsurpassed anywhere. It’s also rare because it was created not by carbonic acid percolating down through the soil but by sulfuric acid coming up from below. Around 20 million years ago, hydrogen sulfide gas began to migrate un...

There’s a place in Siberia that the locals call “The Gateway to Hell.” Technically, it’s a retrogressive thaw megaslump. In plain English, a crater melted into the permafrost. In fact, it’s the largest permafrost melt in the world. It began 60 years ago, when the Russians clear-cut a strip of Siberian forest. This exposed the soil to the summer sun, which began to melt a crater that’s now a half m...

Cacti are native to the Americas and first evolved 30 million years ago—which sounds like a long time—but they’re hundreds of millions of years younger than most other types of plants. They’re specially adapted to dry environments, having transformed their trunks into thick, green, water-storing tissue and their leaves into spines. Cacti grow from half an inch to more than 60 feet in height and ra...

Some paleontologists have recently put forth a controversial idea—that they’ve found a place where the time of year the dinosaurs died is captured precisely in the fossil record. It’s called Tanis, in North Dakota. But it was once the northern end of an inland sea. 66 million years ago, when the Chicxulub asteroid struck the Yucatan Peninsula, it instantly wiped out all life within 1,000 miles. Bu...

Spring is tornado season, so let’s take a look at a few twister myths and how the truth about them can keep you safe. The first myth is that spring is tornado season! While it’s true more than half of those in the Northern Hemisphere do occur in April and May, they can occur in any month of the year. It’s also a myth that tornadoes never strike the same place twice. Some places have had three in o...

Easter Island has little to do with Easter—but new research shows it did once have a very impressive egg hunt. More than a thousand years ago, Polynesians crossed thousands of miles of ocean to reach one of the most remote islands on the planet. They called it Rapa Nui and built a community there. Three hundred years ago, a Dutch captain arrived on Easter day and gave the island its Western name....

Lobsters used to be considered the “cockroach of the sea,” food fit only for indentured servants and prisoners. My, how times have changed. Could the same change be coming for crickets? Today, nearly 40 percent of habitable land is used to raise livestock and their feed. By 2050, the UN projects global population will increase by two billion people—people who will need protein in their diet. There...

Heavy farm equipment is now as heavy as the heaviest dinosaurs—and, surprisingly, there may be some similarities. Today, a fully loaded combine weighs 60,000 pounds—or more! Engineers have worked to distribute their increasing weight across the soil, widening the tires, sometimes putting three tires on each hub. But research has shown these heavier machines compact not just the tilled topsoil but...

For more than 20,000 years, humans have used poison—in hunting, in pest and plant control, and even to kill other humans. Castor bean residue is the source for ricin, which causes multiple organ failure. But it’s used by some indigenous tribes on their hunting arrows. But the deadliest synthetic poison is VX, a nerve agent that stops victims' breathing. Originally developed as an insecticide, it p...