Just how rare are rare earth elements? It depends on their price.

There are 17 REEs, with funny names like gadolinium and dysprosium—and all of them are metals.

Their special magnetic, thermal, and corrosion-resistant properties have led engineers to use them in our most familiar electronics.

The rarest ones are still 200 times more plentiful than gold. And the most common are as abundant in the Earth’s crust as nickel, zinc, or lead.

The challenge is that they’re rarely concentrated enough to mine. And when they are, it takes heavy processing with heat and acid, which produces salty, radioactive wastewater.

California was the largest producer of rare earth elements—till China entered the market.

Lower labor costs and looser environmental regulations allowed China to produce such a large supply so cheaply that U.S. mines closed.

With rare earth elements common and cheap, engineers used them in thousands of products.

But once China dominated the market, they began to raise prices and limit supply, to apply political pressure to electronics makers, like Japan.

But this backfired: Higher prices encouraged mines in other countries to reopen and discouraged engineers from using rare earth elements in new designs.

Which goes to show that rare earth elements, like all resources, are subject to the laws of economics.

Supply often depends on how much we’re willing to pay. If the price climbs beyond that, we start looking for alternatives.

When you look at a cloud, you’re actually looking at billions of microorganisms.

Ever since Darwin found microbes in dust over the Atlantic, they’ve turned up in ever-stranger places:

In dust plumes over mountains. In high-altitude snowfields. And in the tops of clouds.

This means, of course, they’re also in rain. Scientists have identified thousands of species of microbes and fungi living in rain and clouds—able to withstand the harsh temperatures, low oxygen and punishing radiation of the atmosphere.

What we didn’t expect is their complex relationship with clouds and rain.

Clouds are usually born at high altitude, where it’s cold enough for ice crystals to form. To do that, they need a nucleus to form around. Nuclei can be inorganic particles, like dust, salt, or ash. Or they can be organic particles, like microbes.

Recently we’ve discovered that many cloud-dwelling microbes create proteins that mimic the structure of ice crystals, allowing ice—and therefore clouds—to form at higher temperatures and lower altitudes.

As the ice crystals grow and become heavy, they fall through the cloud to become snow, sleet, or rain, carrying the microbes down with them.

On Earth, many of these microbes feed on plant populations, which die and dry up, and the microbes are carried by the wind into the atmosphere again.

This cycle transports microbes around the world, forms more clouds and, with them, more rain.

You’ve probably heard of adventurers skiing down the highest mountain in the world. But did you know that elite cyclists can actually ride up it in a day’s time? Then race down at 80 miles per hour?

You probably guessed that I’m not talking about Everest. It’s still the tallest when measuring purely by height above sea level, or altitude, at just over 29,000 ft.

But by other metrics, there are other contenders.

If you measure from the center of the Earth, the highest mountain is near the equator, where the Earth is 21 km wider than at the poles. By this measure, the tallest is the volcano of Chimborazo, in Ecuador.

But, if you’re starting at the base of the mountain and measuring to the top, the tallest—by a wide margin—is another volcano: Mauna Kea on the big island of Hawaii.

Its summit is just shy of 14,000 ft above sea level, the ocean around Mauna Kea is almost 20,000 ft deep, and the base of the volcano is on the seafloor. This makes Mauna Kea nearly 34,000 ft from tip to toe, a full mile taller than Everest.

Its low humidity and long distance from civilization make Mauna Kea an excellent astronomical observatory, with 13 international telescopes at its summit.

There are roads leading up to them, so if you’re looking for an 8-hr-straight-up bike climb followed by a blistering white-knuckle descent, Mauna Kea may be your kind of mountain.

From a previous EarthDate, you may remember that some mythological creatures were born when ancient cultures discovered fossils and created stories to explain them.

Well, here’s a famous beast that started as a tiny elephant.

During the Pleistocene ice ages, polar ice and continental glaciers held more of Earth’s water, causing sea level to fall.

During low sea-level periods, elephants from Africa walked and swam across a nearly dry Mediterranean to Europe. Once seas rose again, some were trapped on islands like Sicily.

When a population gets stuck on an island, it will often overstress its food reserves and be forced to adapt—something called island rule.

These elephants shrunk to survive on less food, and on Sicily got as small as 3 ft tall and 250 pounds.

Once adapted, they did quite well, with no natural predators…

That is, until man arrived, 11,000 years ago. Overstressing their own food reserves, early tribes hunted the small elephants to extinction.

Some of their bones ended up in caves, where tribes lived or cooked. And thousands of years later, the Greeks discovered them.

The elephants’ skulls were about twice the size of a human’s—with a single hole in the middle where the trunk would have been.

Having never seen an elephant, the Greeks imagined these were the skulls of giants with one large eye: the dreaded cave-dwelling Cyclopes—which then appeared in Greek mythology and rose to fame in Homer’s Odyssey.

The water cycle makes life on Earth possible. And what makes it possible are the incredible properties of water itself.

Earth is the only planet we know of where the three phases of water—solid, liquid, and gas—are present on its surface.

That’s partly because those three phases exist in a narrow temperature window. And the middle phase—liquid water—corresponds to much of Earth’s surface temperature.

This allows our oceans to exist, which are the key reservoirs of the hydrological system. Winds moving across oceans lift huge volumes of water vapor—seven times more than simple evaporation could.

Converting liquid water to gas distills it, leaving salts and impurities in the sea and carrying pure water vapor into the atmosphere. It rises to form clouds and rains down elsewhere.

Three-quarters of that rain falls back into the ocean. The other 25 percent falls on land, where it’s used by all terrestrial life.

But it’s also one of the most powerful forces eroding the surface of Earth.

Gravity pulls rainwater downhill, and over a few million years—a blink of an eye on Earth’s time scale—it can flatten mountains and carry them in rivers, grain by grain, to the sea.

If frozen into glaciers, water becomes a river of ice and rock, grinding down the earth even faster.

The amazing life-giving, planet-shaping properties of water are what make Earth what it is, and we’ll talk a lot more about it on EarthDate.

Every person in the Northern Hemisphere, when they look up at the full moon, sees a face like a smiling snowman—the man in the moon. Throughout history, he has inspired legends.

In many European cultures, he was a man banished to the moon for stealing from his neighbors—or for working on Sunday. (Good thing that’s not a banishable offense today!)

Coastal Germans, recognizing the moon’s tidal connection, believed he was a giant who poured water on Earth to create high tide.

In Norse legend, the man kidnapped two children to have them fetch that water, a story that would become Jack and Jill.

In the Southern Hemisphere, however, the man’s face is upside down, which makes it look like a rabbit—with legends all its own.

The eyes of the man and the body of the rabbit are actually basalt flats caused by ancient lava flows. But why do all people on Earth see this same view?

The answer is something called tidal locking—most moons are tidally locked to their planets.

Soon after the moon formed, the powerful pull of Earth’s gravity created a bulge near the moon’s equator.

Gravity kept pulling the bulge toward Earth, slowing the moon’s rotation till it was perfectly in synch with the moon’s orbit around Earth, meaning that only one side of it faces Earth, and always will.

So what exactly is on the other side of the moon? You’ll have to wait till another EarthDate to find out.

Recently, scientists discovered the fossil of a hadrosaur, a duckbilled dinosaur, which was bitten by a Tyrannosaurus.

A bite on a fossil is not that unusual, but this one helped settle an argument.

Over the past few decades, some paleontologists maintained that T. rex was a ferocious hunter.

Newer theories pointed to his useless forelimbs, small eyes, and huge olfactory chambers.

He wouldn’t have been able to grasp prey and may have had poor vision—but he would have been able to smell a rotting carcass from miles away. In other words, he was likely a scavenger.

But the hadrosaur tail vertebrae in this fossil were fused together around a T. rex tooth—the wound had healed.

This meant that the hadrosaur was alive when it happened, and lived on. Which strongly suggests that T. rex did in fact chase and catch it—almost.

This brought up another question: given his weaknesses, how did the tyrannosaur do it?

A different set of scientists analyzed the leg mechanics of T. rex for bone stress. Proponents of “T. rex the hunter” had pointed to his speed, previously estimated at over 30 miles per hour.

But this new research suggests that the foot bones, carrying his 7 tons of weight, would have shattered at that pace. The tyrannosaur’s top speed was probably just 12 miles per hour.

And maybe that’s why the duckbill got away—T. rex may have been an occasional hunter, but maybe not a very good one.

Many ancient cultures have stories of fantastic creatures. Did all these people simply imagine dragons, gryphons, or giants?

Today, scientists believe they found fossils and, unable to explain them, gave them exaggerated features of the animals they knew and found places for them in folklore.

For instance, we know Greeks and Romans collected fossil bones. They believed these once belonged to their gods and warrior heroes, who were hailed as giants when the huge bones were found.

These fossils, now known to come from mammoths, were displayed in the Roman capital as late as AD 500.

Long before then, different cultures told stories of gryphons, which were part lion, part eagle and protected Earth’s gold.

Where might this story have come from?

In the Gobi Desert, gold would often erode into streambeds with fossils of Protoceratops. Their skulls somewhat resembled contemporary lions, but with a large eagle-like beak.

Earlier still, dragons appeared in Chinese mythology. While many experts today don’t see a direct fossil connection, there’s an ironic link to the present day:

Many villagers still believe in dragons and grind fossilized “dragon bone” into medicines, as they have for 2,500 years. Paleontologists can often follow the sources of apothecary “dragon bone” to find new fossil beds.

No doubt there are some cases where mythical beasts sprang purely from the imagination, not fossil discoveries. But on a future EarthDate, we’ll look at one famous myth that almost certainly did.

Imagine you’re in Chile’s Atacama Desert, the driest nonpolar desert in the world. Understandably, you’re parched. So you head to the local watering hole…where you’re surprised to find a craft beer—made from fog. What?

Deserts have little rain, but if they’re near the coast, they can have fog—which you may remember is just a cloud on the ground, water vapor condensing around particles in the air.

In the Atacama, fogs often roll in from the Pacific, but the water droplets are too small to produce rain. So in the 1950’s, a professor began experimenting with ways to extract water from the cloud.

Following his lead, the villagers of Peña Blanca have strung a series of nets in the mountains. Together, they condense more than 2,000 gallons of water from the fog each day, which is carried by aqueducts into the village.

This water serves people, livestock, vegetable gardens—and an award-winning microbrewery. Their beers are famed for their light body, which some attribute to the lack of minerals in the cloud-borne water.

Chilean researchers estimate that collecting just 4 percent of the water from the Atacama fog would meet the needs of all the communities in the desert, and that a 3-ft by 5-ft net could provide enough water for one person per day.

For these reasons, villages in many countries are now building fog nets, and they could be an important source of water—and beer—in coastal deserts around the world.

Next time you hear a bird singing, stop for a second to listen. Even the most common birds can do amazing things.

The cardinal, for instance, has the range of a piano, though higher on both ends. And he can span it in a tenth of a second. No human can come close.

The wood thrush can sing one note, a different note on top of that, and trill them both independently. It’s like a soprano duet in one 2-oz animal!

How can they do these incredible things? The secret is their voice box.

Our larynx has one chamber. Theirs, called the syrinx, has two. Ours sits in our throat; theirs, at the base of their trachea. At that location, each chamber has access to a lung.

In this way, the most accomplished bird singers can control each side of their voice box separately, even take small breaths in one side while singing from the other, to keep their song continuous.

If that weren’t enough, some birds know up to 1,000 different songs.

You may remember from a previous EarthDate that for most of Earth’s history, animals couldn’t hear sounds—or make them. So it’s particularly impressive that birds have developed this ability.

In fact, one of the ways we know that ancestors of modern birds lived through the asteroid extinction that wiped out the dinosaurs is that we’ve discovered fossils from before the impact with a voice box similar to those of today.

The syrinx is one of nature’s greatest hits. It may be an oldie, but it’s a goodie.