Where does gold come from?

In medieval times,

alchemists tried to achieve 

the seemingly impossible.

They wanted to transform lowly lead

into gleaming gold.

History portrays these people

as aged eccentrics,

but if only they'd known that their

dreams were actually achievable.

Indeed, today we can 

manufacture gold on Earth

thanks to modern inventions

that those medieval alchemists

missed by a few centuries.

But to understand how this precious metal

became embedded 

in our planet to start with,

we have to gaze upwards at the stars.

Gold is extraterrestrial.

Instead of arising 

from the planet's rocky crust,

it was actually cooked up in space

and is present on Earth 

because of cataclysmic stellar explosions

called supernovae.

Stars are mostly made up of hydrogen,

the simplest and lightest element.

The enormous gravitational pressure

of so much material

compresses and triggers nuclear fusion

in the star's core.

This process releases energy

from the hydrogen,

making the star shine.

Over many millions of years,

fusion transforms hydrogen 

into heavier elements:

helium, carbon, and oxygen,

burning subsequent elements faster

and faster to reach iron and nickel.

However, at that point nuclear fusion

no longer releases enough energy,

and the pressure from the core peters out.

The outer layers collapse into the center,

and bouncing back from this sudden

injection of energy,

the star explodes forming a supernova.

The extreme pressure

of a collapsing star is so high,

that subatomic protons and electrons

are forced together in the core,

forming neutrons.

Neutrons have no repelling electric charge

so they're easily captured 

by the iron group elements.

Multiple neutron captures enable

the formation of heavier elements

that a star under 

normal circumstances can't form,

from silver to gold,

past lead and on to uranium.

In extreme contrast to the million year

transformation of hydrogen to helium,

the creation of the heaviest 

elements in a supernova

takes place in only seconds.

But what becomes of the gold

after the explosion?

The expanding supernova shockwave

propels its elemental debris

through the interstellar medium,

triggering a swirling dance 

of gas and dust

that condenses into new stars and planets.

Earth's gold was likely delivered this way

before being kneaded into veins

by geothermal activity.

Billions of years later, we now extract

this precious product by mining it,

an expensive process that's compounded

by gold's rarity.

In fact, all of the gold 

that we've mined in history

could be piled into 

just three Olympic-size swimming pools,

although this represents a lot of mass

because gold is about 20 times 

denser than water.

So, can we produce more 

of this coveted commodity?

Actually, yes.

Using particle accelerators, we can mimic

the complex nuclear reactions

that create gold in stars.

But these machines can only construct gold

atom by atom.

So it would take almost the age 

of the universe to produce one gram

at a cost vastly exceeding 

the current value of gold.

So that's not a very good solution.

But if we were to reach 

a hypothetical point

where we'd mined 

all of the Earth's buried gold,

there are other places we could look.

The ocean holds an estimated 

20 million tons of dissolved gold

but at extremely miniscule concentrations

making its recovery too costly at present.

Perhaps one day, we'll see gold rushes

to tap the mineral wealth

of the other planets of our solar system.

And who knows?

Maybe some future supernova 

will occur close enough

to shower us with its treasure

and hopefully not eradicate 

all life on Earth in the process.