Episodes

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. ...

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...

Wondering what to get that special someone for Halloween? How about a bouquet of corpse flowers? Of course, you’ll have to go all the way to Indonesia to get them. And it would be a very, very large arrangement. There are two types of corpse flowers, and both emit a strong odor of rotting meat to attract flies and beetles to pollinate them. Titan arum lives up to its name, with flowers topping 10 feet in height. To produce a bloom of such staggering proportions, it spends a few years as a small ...

Phoenician soldiers, when injured in battle, would shave bronze from their swords into their wounds. Why? For the copper. Copper is often found in its pure state, rather than bound in ore, and is easy to bend. This made copper the first metal to be shaped by humans into useful implements around 10,000 years ago. The Copper Age lasted 5,000 years, until someone realized they could add tin to copper to make bronze, which was easier to melt and cast, harder as a finished product, and better for too...

Have you ever seen a gecko walk straight up a glass door, or sprint upside down across a ceiling, and wonder, “How can they do that?” To get the answer, you’d need an electron microscope. At 200× magnification, you’d see the gecko’s toes are covered with tiny hairs called setae. Zoom in closer and at 1000×, you’d see that the setae are actually bunches of hairs, like in a hairbrush. Much closer, at 55,000×, you’d see that each one of those hairs splits again into hundreds of branches of spatulae...

California gray whales, like several other whale species, migrate from arctic feeding grounds in summer to warm equatorial waters in winter to birth their young. This migration can be more than 13,000 miles—the longest on Earth. Scientists think they may use magnetoreception, navigating according to Earth’s magnetic field. New findings somewhat corroborate that, but with a wrinkle we can’t explain. It’s not uncommon that whales will get lost or injured along the route, strand themselves on the c...

Around September 23rd and March 20th each year, visitors gather at ancient monuments to witness the equinox. On these two days, day and night are equal everywhere on the planet. The sun rises exactly in the east and sets exactly in the west. Ancient architects, astronomers, and priests collaborated to align many structures with the equinox sun to create spectacular light effects. In a 5,000-year-old underground Celtic temple, the rising sun penetrates a long shaft to light an engraved wall. At a...

When passengers boarded a British Airways flight from New York to London on February 8, 2020, they had no idea they were about to make history. Once their 747 reached cruising altitude, the pilots directed the plane into a jet streak, a fast-moving current of air that sometimes occurs in winter. The streak rocketed the plane to a ground speed of 825 miles an hour, cutting travel time by 25 percent and setting a record for subsonic aircraft making the trip. The surprised passengers arrived in Lon...

On another EarthDate you heard that bees are dying. While it’s common for a hive to lose 15% of its bees each winter, rates since 2007 have sometimes hit 40%. This has scientists concerned, and after a decade of research, they’ve traced the bees’ troubles to several factors. First, stress. A decrease in wild acreage means fewer wild bees, so that more commercial bees are needed for pollination. This has the hives traveling farther and more frequently. Rising temperatures also have an impact, mak...

Nickel is in demand because it’s used in lithium ion batteries, common alloys such as stainless steel, and new super alloys for the aerospace and wind turbine industry. But mining and smelting nickel is energy intensive, using a great deal of diesel fuel and coal. And the after-products are environmentally dangerous. Luckily, we’ve found that nickel can grow on trees. Or more specifically, shrubs. Metals are toxic to most plants, which don’t grow in metal-rich soils. But some 700 species are hyp...

Even if you’ve watched documentaries about honeybees, you may know little of their remarkable life within the hive. A queen will lay a million eggs in her 5-year lifetime, which she places in wax brood cells. Fertilized eggs grow into sterile female workers. Unfertilized eggs become male drones. When the queen gets old, nurse bees bathe regular female larvae in royal jelly, which turns them into queen larvae. The queen that emerges first will kill the other larvae to become sole heir to the thro...

Honey is a miraculous substance, containing enzymes, vitamins, minerals, and antioxidants. But it’s not the only amazing thing bees make in the hive. Honey starts as nectar that bees gather from thousands of flowers on foraging flights. The bees store the nectar in a special sac next to the stomach. On returning to the hive, they transfer it to the mouths of waiting worker bees. Workers ingest and regurgitate the nectar over and over for several minutes. Their digestive enzymes convert the sucro...

Bees make over $300 million worth of honey, beeswax, propolis, and other products each year in the U.S., which we eat and use in medicines, cosmetics, even varnishes. But the real big business of bees is the billions of dollars keepers earn pollinating crops. Bee colonies are treated, and valued, like livestock. The keepers move the hives to the best positions for most effective pollination on a strict schedule, following the flowering of crops across the country. They start in February, in Cali...

It seems that Australia’s modern highways may have been laid out according to the stars. Australian Aboriginals, like many ancient cultures, have an elaborate oral history passed down through generations to help them navigate and find food and water in their desert environment. This knowledge base uses visual memory aids from the land… and the sky. When ancient aboriginal navigators found a successful path through the desert, they looked for a path in the stars that mimicked it. They’d use stars...

You’re about to hear what may be the oldest story ever told. In another EarthDate, we talked about how Australian Aboriginals remember star maps using songs. But their oral history has preserved much more in stories that corroborate ancient geological events. For instance, they tell of a dramatic sea-level rise long ago that inundated areas of the coast. Many tribes, separated by great distance and different languages, tell the same story. And the details match the geological record of 7,000 yea...

In many parts of the U.S., what we call “locusts” are actually cicadas—that plug-shaped insect that sings in the trees. But especially in Africa and the Middle East, “locusts” are large grasshoppers occurring in massive swarms that can devour crops across the region. These grasshoppers have undergone a strange metamorphosis. In normal times, they’re a shy, solitary desert hopper. Heat and drought control their numbers, and they’re not a threat to agriculture. But every few decades—when heavy rai...