Throughout the Apollo missions, NASA believed there was no water on the Moon.

In the nearly one thousand pounds of rock and soil samples that these missions brought back, they did find traces of water. But they assumed these were contamination from gathering and transport.

Then in 2008, the Indian space agency launched a Moon orbiter carrying NASA’s Moon Mineralogy Mapper—or M3—which was designed to search for minerals, like water.

The tilt of the Moon’s axis prevents sunlight from reaching into some lunar depressions.

M3 used infrared light absorption to discover ice hidden in the dark corners of these craters— especially near the frigid lunar poles.

But the Moon’s atmosphere is too thin to keep water from escaping into space. As it dissipates, how is it being replaced?

Scientists realized that solar wind bathes the Moon in hydrogen ions for three weeks of its four-week orbit around Earth. The hydrogen reacts with oxygen compounds in Moon rocks to form water.

During the one week of full moon, when the Moon is hidden behind Earth, it’s also shielded from the solar wind.

At that time, Earth wind—the tail of our magnetosphere, which is deformed by solar wind into a teardrop that stretches toward the Moon— also bathes it in hydrogen and oxygen.

Without these constant supplies of the building blocks of water, from both Sun and Earth, the Moon would, in fact, be totally dry.

In a few rare places in the world, there are salt lakes that are flamingo pink.

To understand what gives them their bright color, we should first understand what makes flamingos pink.

The birds spend much of their lives wading and feeding in shallow lakes that aren’t pink but are salty and hold the flamingo’s favorite food: brine shrimp.

These shrimp are pink, colored by high concentrations of beta-carotene—the same pigment that makes carrots orange. After a couple years of eating shrimp, flamingos, which start out gray, have consumed enough beta-carotene to turn their feathers pink.

But what makes the shrimp pink? It’s also something they eat.

In these salty lakes lives a particular kind of microalgae adapted to the saline water.

It starts out green, but to protect itself from UV radiation, produces a pigment that acts as a natural sunblock: beta-carotene. Which turns the algae … pink.

So, pink algae make pink shrimp, which make flamingos pink.

But what about the pink lakes? They don’t have any flamingos in them. In fact, they’re so salty that almost nothing can live in them, except that microalgae.

And there’s so much of it that it colors the water red. When the sun shines through it and bounces off the light-colored bottom, we get a bright, flamingo-pink lake.

These pink lakes are valuable sources of both salt and beta-carotene, and for many years people have visited them to collect both.

Monkeys make tools. Birds build houses. And ants grow agriculture.

Bees live in complex societies, and many creatures use basic language to communicate.

It could be argued that the biggest differentiator of humans from other animals is that we have harnessed energy—first and still foremost in the form of fire.

Fire kept us warm, allowing early humans and our ancestors to spread into harsher climates. It helped us hunt, then gave us the ability to cook. We gathered around the fire at night, which helped us develop language, share stories and build cultures and religion.

Scientists have theorized that fire was so instrumental to human development, we could not have evolved without it.

Cooking with fire broke down tough animal protein and plant matter, making things that may not have been edible now digestible and more nutritious.

This may have given prehumans the calorie and protein surplus to develop bigger brains, to build stronger communities, to spend more time raising children and passing knowledge to them.

Scientists have found evidence of hearths, places to cook and gather, from as far back as one million years ago.

Four-hundred thousand years ago, hominids may have realized they could strike flints to make sparks, which made fire portable.

And today, three billion people still get most of their energy from burning wood and biomass.

Humans make fire, but fire also made humans.

For billions of years, there was no fire on Earth.

There was heat to ignite it, like volcanic eruptions and lighting strikes. But fire lacked two very crucial ingredients: fuel to burn, and oxygen to feed the flames.

Ironically, plants would provide both.

Fire is a chemical reaction where fuel oxidizes to produce heat and light energy, carbon dioxide, water vapor and other gases.

Fire can start when there’s about 13% oxygen in the air, but it won’t stay lit.

It will burn steadily at 16% oxygen, improving to about 23%, and plateauing at 30%.

Land plants evolved 470 million years ago, consuming carbon dioxide to perform photosynthesis and producing oxygen as a by-product.

As they grew, evolved, and covered more of the Earth, plants finally drove Earth’s atmosphere to above 13% oxygen.

And, 420 million years ago, the first fires started.

Plants continued to thrive, and swampy forests eventually covered the globe during the time of dinosaurs. Oxygen levels hit 29% and wildfires became very common.

Around 50 million years ago, oxygen levels stabilized at 21%, as fire and photosynthesis struck a balance: Fire consumes plants and oxygen and makes carbon dioxide. Plants consume carbon dioxide and make oxygen.

A perfect cycle.

Here’s a fun experiment you can try at home to make miniature cold lightning using rocks from your yard, or candy.

First, look for some quartz pebbles. Preferably milky white ones.

Next, find some wintergreen Life Savers—or white sugar candies will do.

Then grab some safety glasses, because you’ll be smashing things.

Now go to a darkened room, let your eyes adjust, and rub the pebbles together. Try different levels of friction and speed. You should see a flash of light in one or both pebbles as friction causes them to luminesce—without producing a spark.

This is called triboluminescence, which happens when some materials rub together or break.

Now try crushing the Life Savers with a hammer or pair of pliers. The wintergreen oil will also fluoresce, increasing the effect.

Scientists are still not exactly sure how this happens. It’s thought that the friction or cracking causes positive and negative charges to separate. When they recombine in the presence of nitrogen in the air, they produce cold light, without heat, similar to lightning in a cloud.

Besides being a neat trick, researchers are trying to put it to use. They’re experimenting with integrating triboluminescent materials into high-value items, like bridge structures or spacecraft parts.

Using special sensors that can see the faintest luminescence, they hope to observe fractures developing before critical failures could occur. A cool benefit from cold lightning.

Some of the loudest sounds in the ocean are air guns, fired by ships doing seismic studies of the seafloor.

The blasts can interfere with the communication of whales for a thousand miles around. So, scientists thought, what if they could use whales to do the studies instead?

In a seismic study, sound waves from a ship travel down through the water, through the ocean floor and into the geologic layers below.

They reflect off these layers and bounce back to other ships, where powerful computers analyze them to build geologic models of the Earth below the ocean.

The songs of fin whales, when converted from water to air, are as loud as a jet leaving an aircraft carrier, but in a similar low range as the air guns.

Scientists used hydrophones on the seafloor to record the whale song and its reflections, then fed that data through the same seismic computer programs.

Turns out the whale song did in fact penetrate the subsurface, down to about 8,000 feet, and could successfully be used to build similar geologic models.

Scientists now plan to analyze the higher-frequency songs of other whales, seals and dolphins to see if they can add detail to the models.

Air guns are still louder and penetrate deeper, so whale song won’t replace seismic ships for critical study.

But recording and analyzing the songs of sea mammals could allow geologic studies where seismic ships are too expensive or impractical.

For decades, Death Valley held a mystery that scientists could not solve.

Large rocks were slithering across the valley floor, traveling hundreds of meters, leaving long tracks behind them.

But no one had seen them do it or could figure out how it happened.

So, scientists fitted rocks with GPS trackers and set up remote cameras to try to capture the rocks in motion.

Because the movements could be separated by decades, they expected this to be “the most boring experiment ever.”

But just two years in, they got very lucky: they were in Death Valley one cold December to change the GPS batteries … and saw the rocks move in person.

And figured out the rare combination of conditions that made it happen.

The valley floor had to cover with water, from rain or melting snow. The night had to be cold enough to form a thin sheet of ice across its surface.

The next day had to be warm enough to break up the ice into large floating panels, up to 50 feet wide.

Then a light, steady wind was needed to gently push the ice islands across the water, slowly nudging the rocks along with them, across the slippery mud bottom.

By midday, the ice and water had evaporated, and the scientists saw long trails behind the now displaced rocks. Their cameras and GPS trackers captured it all.

If your birthday is in August, your birthstone is peridot. And if you have one, you can be sure it came from deep within the Earth—or deep in outer space!

Peridot is the gem name for a gem-quality example of olivine.

Olivine is very common inside the Earth, where it makes up an astonishing 50 percent of Earth’s upper mantle. But it’s much less common on the surface.

It’s found where tectonic forces push mantle up and over Earth’s crust, or where volcanic activity brings up mantle in the form of lava, which can contain peridot crystals.

The most celebrated source of peridot was the tiny Egyptian island of Zabargad, which was pushed up in the region that is now the Red Sea when the African and Asian plates collided 600 million years ago.

Zabargad has been mined since the third century BC and has produced some of the world’s best peridot gemstones. Today, the largest mines are in Myanmar and Pakistan.

A much rarer source of olivine is meteorites that break off from a planet or asteroid large enough to have a mantle then enter Earth’s atmosphere.

These spectacular meteorites contain olivine crystals held in a dark nickel-iron metal matrix. Of the thousands of meteorites found, only 45 contain olivine.

So, if you have a peridot, you can marvel at the long distance it traveled to get to you from deep inside—or far outside—the Earth.

In another EarthDate, we talked about Earth’s magnetic polarity reversing.

But sometimes the poles don’t flip, they just go on an excursion—with potentially drastic consequences.

A polar excursion happens when the pole moves more than 45 degrees from Earth’s rotational axis. This happened 12 times in the last million years.

Forty-two thousand years ago, there was a particularly wayward North Pole.

It wandered down to New York, then all the way to Antarctica, before rising back up to its original position.

The excursion took nearly a thousand years. While the pole traveled, Earth’s magnetic intensity fell, to as low as 6 percent—which is what caused the trouble.

You may remember from another EarthDate that Earth’s magnetic field protects us from cosmic rays. With it almost gone, much more radiation could reach Earth.

New data from this period suggests that increased cosmic radiation eroded the ozone layer and altered global wind patterns, causing dramatic climate change.

Ice sheets advanced in the higher latitudes. Drought swept across the middle latitudes. Megafauna went extinct in Australia. Neanderthals went extinct in Europe.

And cave art flourished, perhaps as humans took shelter from weather and harmful solar radiation.

It’s hard to say how much is correlation versus causation. But the poles are always wandering. If a pole goes on an excursion, we may find out for ourselves the effects of a reduced magnetic field.

Compasses point north. Until one day, they’ll all point south—as they have before.

In 1905, a French geologist discovered a lava field with some very strange properties. Iron within it was magnetized in reverse. What should have been north was south.

After much pondering, he realized this could only be possible if Earth’s magnetic poles were reversed at the time the lava was flowing. When it solidified, it preserved that reversed magnetic orientation.

It took 50 years for other scientists to accept the idea that Earth could change its polarity. But when they did, a frenzy of research began to try to document the phenomenon.

First, they looked for more places where a reversed magnetic field was memorialized in iron compounds.

They found them along spreading ridges in the Atlantic, where tectonic plates pull apart and new iron-rich rock is pushed up, producing new crust for the planet.

In 1959, they mapped alternating stripes of reversed magnetic orientation in several places along the Atlantic ridge, then dated each stripe of rock.

To their surprise, they discovered that Earth had reversed polarity hundreds of times, with episodes lasting tens of thousands to millions of years before reversing again.

They also realized that Earth’s magnetic poles are always on the move, sometimes without making a full reversal.

We’ll talk more about the mess this could make on another EarthDate.