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.