Derek: The world is full of mysterious places you can see from high above using Google Earth, but what's really going on down there, and why? I'm Derek Muller, a scientist, educator, and filmmaker, and I'm going to unearth the stories behind these amazing places. Just drop a pin and I'm off.

( mysterious music ) ♪ ♪ I am here in the middle of the Utah desert surrounded by sandstone cliffs and red rocks and this scrub. But that is not what I'm here for. What I'm looking for should be right over this ridge.

♪ ♪ There are electric blue ponds in the middle of the Utah desert. When I saw them on Google Earth, I had so many questions, like what are they? Why are they here?

And why do these colors keep changing? One person thought this might be a top-secret NASA experiment, since, after all, you can see them from space. Someone else suggested, "Well, maybe they're just really large swimming pools.

" What are those? What do you think? Like a geo kinda thermal thing?

Like a solar thing? Like, they come up from the ground? It's gotta be some sort of, you know, science experiment of some kind.

They sort of look like rice paddies, 'cause they're on ledges. Derek: The truth is far more fascinating than any of those guesses. These technicolor pools are full of something that's been prized throughout human history.

What are they used for and how are they connected to fireworks, George Washington, soap, glass, Gatorade, gunpowder, a pioneering scientist named Humphry Davy, every other person on the planet, and lots of money? ( birds crying ) ♪ ♪ The answer begins with a pot and a hardwood fire. This is a 1,500-year-old recipe.

Take some hardwood and burn it, not for the heat, but for the ash. Put the ash in a pot and add water. Now, there are a lot of different chemical compounds in there, but the one I'm after is water soluble, so it dissolves.

Strain out the solids and you'll find the solution is slippery. Put it in a pan and let the water evaporate in the sun, and what you're left with is this crystalline substance. All that work for this.

It is one of the most important chemicals people have been making for centuries, and it's called potash because that is exactly where it comes from. In 1807, British scientist Humphry Davy got some damp potash and put electrodes into it. Then he connected them up to a battery, and what he observed was the formation of tiny metal globules, and as they burst through the crust of the potash, they spontaneously caught fire.

Davy had discovered a new element, so naturally, he named it pot-ash-ium. Potassium. Yes, that is where the name of the element comes from.

It comes from the potash. ♪ ♪ When you hear the word potassium, many people think of bananas or Gatorade, and that's true, these foods are good sources of potassium, but it's not pure potassium. This is a piece of pure elemental potassium.

It's a metal, but I can squish it with my fingers. And this had to be created in a lab because it is so reactive, it'll react with anything. This piece was kept submerged under oil so it doesn't react with the water in the atmosphere.

It's an incredibly reactive substance, and to demonstrate that, I'm going to put a piece of it in this water. I'm gonna weight it down so the potassium doesn't just sit on the top but actually will sink down to the bottom. Three, two, one.

- ( pops ) - Oh, yeah! - ( pops ) - Oh! - ( pops ) - Oh, yeah!

I did not expect it to do that. That is awesome! Are you kidding me?

Yeah! Of course, I've seen this demo before, but never with such a huge explosion. ( in slow-motion ) Oh, yeah!

I think the key was weighing it down so it didn't just spark on the surface. Potassium reacts with water, forming potassium hydroxide and hydrogen gas. It also releases a lot of heat, so when the hot hydrogen gas hits the atmosphere, it spontaneously combusts.

Potassium is so reactive because it has one electron in its outermost shell, which is easily removed, and that's why we never find metallic potassium in nature. Now, the word potash originally referred to that stuff which, chemically, is potassium carbonate, but potash has become a catchall term referring to lots of potassium-containing compounds. So the potash that Davy was using was actually potassium hydroxide.

And this is not the last time we're gonna hear from Davy. But why is potash so important to people? I'm on the trail of Potash.

Look at that. ♪ ♪ All right. This is bacon grease.

For centuries, it was used in making soap. Take some animal fat, add potash, and a chemical reaction creates a primitive liquid soap. And look at that.

This is incredible. ( laughs ) I'm getting a real lather going here. That's not bad.

Take a look at that. The potash soap actually worked. Potash was also used to make glass.

Glass is mostly sand, silicon dioxide, but add some potash and you reduce the melting point. This makes glass less brittle and easier to work with in early furnaces. ♪ ♪ ( Western music ) ♪ ♪ If you take the potash solution and add bat guano or manure, crystals of a different potassium compound form: potassium nitrate, also called saltpeter, and it's one of the core ingredients in fireworks and gunpowder.

♪ ♪ Get ready. ( laughs ) That was awesome! Saltpeter made from potash infused gunpowder in the muskets and cannons of battles fought in China, Europe, and the American revolution.

( slow-motion explosion ) Potash was by far the main chemical product of the early American colonies and a substantial source of revenue. By 1788, there were 250 potash works in the state of Massachusetts alone, places where wood was burned on a massive scale just for its ash. In 1790, the newly-independent U.

S. government issued its first ever patent. It was for an improved process for making potash.

The patent office has now issued over 10 million patents and the literal first one is for potash. It was signed on July 31, 1790. Look closely at the signature.

It's signed by none other than President George Washington. That should give you an idea of how important potash was. The demand for potash was so high that across Europe and the eastern U.

S. , forests were decimated. Unfortunately, it required a huge amount of lumber to create just a small quantity of potash.

Then in 1861 in Germany, they started producing potassium from a different source. They found it not in plants or any living organism, but in a rock. This is potassium chloride in its natural mineral form.

Now, this also gets the name potash even though the name originally referred to ash in a pot, potassium carbonate. It changed everything. Germany established a near monopoly in the potash supply.

They had so much of the stuff that they started looking for new uses. Well, they did experiments sprinkling this stuff on farmers' fields, finding that this acts as an excellent fertilizer. That's because potassium, along with nitrogen and phosphorous, help crops grow far larger and makes them more drought-resistant.

The downside was, in 1910, just four year before the start of World War I, the Germans cut off potash exports to the world. Their preemptive first strike was depriving the world of potassium, something countries had become dependent on to feed their growing populations. The U.

S. became so desperate for other sources of potassium that in 1911, Congress appropriated money to find domestic sources. Sites discovered near Searles Lake, California, Carlsbad, New Mexico, and Moab, Utah, became potash paydirt.

( inquisitive music ) ♪ ♪ But the potash rocks weren't on the surface. They were deep underground, so potash had to be mined out. ♪ ♪ But how did it get here in the first place?

I'm meeting Mike Coronella, a Moab guide who knows the history of this area. ♪ ♪ So the layer that the potash is found in is called the Paradox Formation, and it was created by an inland ocean that kept retreating, returning, retreating, and returning. The water would evaporate and leave behind salt and other evaporites like potash.

Salt in the ground is very much like an air bubble in water. Geologically, it wants to float. It's literally pushing up against the crust here.

And they used to harvest it underground like coal, you know? Scraping it out, throwing it on the narrow-gauge rail up to the surface. But salt also likes to trap oil and gas, and there's oil and gas in this area.

And I believe it was 1963, as they were mining the potash, they hit a pocket of gas and there was a big explosion, major loss of life. Derek: This tragic explosion occurred at 4:40 in the afternoon on August 27, 1963. 18 men died.

Investigators concluded, the disaster was caused by the ignition of combustible gas by electric arcs, sparks, or an open flame. Miners' electric tools or lights or, back in the old days, candle flames could ignite the natural gas, leading to huge explosions. ( explosion pops ) But there was an invention made to prevent such explosions, an ingenious lamp.

This wire mesh disperses the heat from this flame rapidly enough to prevent igniting the gas outside the screen. This is called the Davy lamp after its inventor and also the discoverer of potassium, Sir Humphry Davy. Without the Davy lamp, the candles could ignite methane in the mine.

And if a mine is full of methane and something ignites it, well, this is what it looks like. Okay, guys. Let's do it.

Producer: In three, two, one. Wow. That was incredibly fast.

Can I watch that back? This footage is shot at 1,000 frames per second. ( tense music ) So it ignites down here at the bottom, and once that spark takes hold, all that gas is burning, and as it does, it releases heat, which causes the gas to expand, and so it accelerates through all the shafts of the mine, getting faster and faster all the way up to the top.

You know, unlike out here in the atmosphere, where, you know, combustion can dissipate and there's a lot of fresh air that can rush in, in the mine, you just have that methane gas. Once there's a single spark, it basically sets the whole place ablaze. Mining is one of the most dangerous professions, so if you don't have to go down in a mine, it's better not to.

( country music ) ♪ ♪ A year after that fatal explosion in 1963, a mining company based in Saskatchewan, Canada, stumbled upon a safer way to mine potash. What they do at that mine is, they pump water from the Colorado River deep underground. It goes down 3,900 feet.

That is where the potash deposits are. Now, that water dissolves the potash salt, so we get a briny solution down here. Then they get forced back up to the surface, where that brine solution is pumped into these ponds.

Here, the water evaporates into the air, leaving you with that potash that you wanted to get. In a sense, the water molecules are like your little miners going in there to get the potash out so you don't have to. These are the ponds that we're looking at.

( investigative music ) ♪ ♪ It's a nice drone, man. So you trust me to fly this thing? I was thinking if we do some dual operator.

- Okay. - So I can fly it. - Uh-huh.

- And you'll have full control of the camera. ♪ ♪ Google Earth gives you this bird's-eye view, right? But you're so high, it's tough to make sense of it.

but it's really from here that you can see what these ponds are all about. You have the hot Utah sun and this dry air. So these are evaporation ponds.

They're evaporating the water off to get to that salt, to get to the potash which is in the water. And it just looks so beautiful from up in the air. There are 23 ponds spread over 400 acres, and it takes months for each one to evaporate.

There are 2 billion tons of potash in the Paradox Basin alone, and at an average price of $330 a metric ton, the potash harvested here could potentially generate billions of dollars. The color of these ponds changes over time. A full, fresh pond is a deep blue color, but over time, as that water evaporates and it gets shallower, we see seafoam green ponds, and further along the line, you get these sort of tan colored ponds.

Ultimately, when all the water is gone, you are left with this white crystalline substance. That is the potash, and they scrape it up with these vehicles. But if the potash crystals are white, then why do these ponds appear so blue?

The answer is in here. It is copper sulfate. See those copper sulfate crystals?

Well, if I add them to the water, they dissolve, dying the water blue. So the copper sulfate is in the water because it prevents the growth of algae and other living organisms. Plus it's this dark blue color, which absorbs more sunlight, more energy from the sun, and that helps the water evaporate faster.

( soft music ) If you can believe it, fertilizer now supports half of the world's population. Every other person owes their existence in part to innovations like this: harvesting potash and other minerals that are essential for the growth of our food. But increasing the efficiency of growing food doesn't just mean this planets can support more people.

It also means that they can explore different ways of life. You know, before the advent of agriculture, when our ancestors lived as hunter-gatherers, we spent all day every day just finding food. But once we could grow our own crops and these days, now that we can do it so efficiently with the help of fertilizer, that totally changes the game.

It frees up most people's time to do other things, to be artists and musicians and sports people and science communicators. So potash itself is irreplaceable. It has helped us make the modern world what it is today.

And that's what these blue ponds have to do with George Washington, Gatorade, fireworks, Humphry Davy, every other person on the planet, and untold riches and how gunpowder, soap, and glass all came out of a pot that was filled with ash and water centuries ago. In today's digital world, few mysteries remain, but there are some. What is this strange horse doing in the middle of the British countryside?

Why does this mountain look like a person? And what is this abandoned city off the coast of Japan? That's where I'm headed.

The Explosive Element That Changed The World