Original subtitles

Narrator: This is the story of a remarkable atom.

Just one of an inconceivable number of

atoms that helped create the world we know.

Toxic, but life giving.

Fragile, yet powerful.

Taking part in countless chemical

reactions, yet indestructible.

You could breathe in atoms once breathed in

by Caesar, Cleopatra, or Genghis Khan.

Blasting through earth's history,

they are a crucial part of earth's most

important events.

Shaping evolution.

From some of the first life forms,

to the giant insects of the coal swamps.

Helping life invade dry land.

Playing a key role as dinosaurs conquer

earth, and giving energy to more familiar

creatures.

Yet this atom creates so much precisely

because it's so destructive.

Building up in earth's early atmosphere,

it killed most life.

Today we can't live without it.

The atom.

Amazing on its own.

With a chemical partner,

it transformed earth.

We didn't know oxygen existed until the 18th century.

Antoine Lavoisier and his wife Marie-Anne are

intrigued by the way materials burn.

At the time, scientists believe burning is

caused by the release of something called

phlogiston, found in all flammable material.

But Lavoisier suspects that air contains

different gasses, each with different

properties.

He and his wife try to isolate them.

When he slowly heats mercury it turns into a

red powder.

And there's one-fifth less air in the flask.

One of the gases must have been absorbed.

Reheating the mercury releases this gas back

into the atmosphere.

This was the gas they were looking for.

Lavoisier calls it "oxygen".

Today, we call the gas O2,

because it's 2 oxygen atoms bound together

and we know much more about why it behaves

the way it does.

A single oxygen atom consists of 8

electrons, orbiting a tiny nucleus occupying

distinct shells.

But two of these shells have space for another

electron.

Desperate to fill these spaces,

oxygen is greedy for more electrons.

It takes from wherever it can,

making it one of the most "reactive"

chemicals on earth.

If we follow this particular atom we'll

see just how reactive.

The first surprise is that this atom's life

didn't start on earth.

This particular atom was born billions of

years ago, in a distant corner of the galaxy.

The story begins with a dying star.

The star has been collapsing for more

than 10,000 years, and at its core,

both temperature and pressure have been rising.

Atoms squeeze together creating ever bigger

ones, new elements with new properties.

Every oxygen atom is made this way.

Forged in the heart of a dying star.

But this is the last one this star will ever

make.

Because now it's making larger and larger atoms

that are no longer oxygen atoms,

until it runs out of fuel.

Finally the core of the star implodes,

then explodes.

A supernova.

All of the star's atoms blast across the

universe.

But in the vastness of space it's alone.

The only time it will exist as a single atom.

Eventually it slows down,

combining with other atoms to form molecules

that clump together, forming tiny particles

of dust.

Gravity draws dust particles into ever

bigger lumps, until 10 million years after the

supernova, planet earth is born.

And the star's last oxygen atom is here

combined with two hydrogen atoms in a

molecule of H20.

Water.

Water in the atmosphere condenses to create the

first oceans.

This is where life begins.

At first just tiny bacteria cells break

apart dissolved chemicals to get their

energy.

But three and a half billion years ago some

bacteria cells learn to harness the power of

sunlight.

When sunlight strikes these cells,

the energy passes along a chain of chemicals

from one atom to another,

until it is used to build new cells,

a process called "photosynthesis".

As it does so, water molecules tear apart.

But an oxygen atom can't exist alone so it

combines with another unwanted oxygen atom

and creates a molecule of oxygen gas.

Our last atom from the dying star is half of

the first molecule of O2.

This is a major milestone in the

history of our planet.

Photosynthetic bacteria produces more and more

oxygen.

But where does it go?

Not into the sea or the atmosphere above.

Oxygen is so reactive it's always looking for

new partners.

It isn't hard to find one.

In the oceans, volcanoes spew out

chemicals from deep within the earth.

Among them is iron.

O2 loves it and forms a new molecule.

But the new molecule is soon torn apart.

Our last oxygen atom is now part of a water

molecule while its partner drops to the

ocean floor, shackled to iron.

Planet earth is rusting.

This ancient story is recorded for posterity

in thick red bands found in some rocks at

the bottom of the ocean.

But iron ore is more than just a stunningly

beautiful record of earth's history.

Iron has shaped the destiny of humanity.

Before iron is forged into a hard metal,

it has to be released from oxygen's grip.

It takes a lot of energy to separate the

iron from the oxygen atoms.

So iron ore is mixed with limestone in a

blast furnace and heated to more than

3,600 degrees Fahrenheit,

hot enough to force oxygen out and release

the pure molten iron.

Now the metal is forged and put to work.

The attraction of oxygen to iron is

incredibly strong.

And we can thank three-and-a-half-billion

years of oxygen in our oceans for the

availability of iron today.

But billions of years ago earth is undergoing

great change.

The more dry land that forms,

the more iron-rich volcanoes erupt above

water, creating unfavorable conditions

for iron to soak up oxygen.

These volcanoes are much hotter than those

on the seabed.

They spew different chemicals already bound

to each other in stable compounds and immune to

reactions with oxygen.

So around two and a half billion years ago,

oxygen gas builds up in the atmosphere.

It's a disaster.

Global pollution worse than any in our own

time.

For billions of years life had consisted of

bacteria getting energy from breaking down

sulphur compounds in an oxygen-free

environment.

For these bacteria, oxygen is a deadly

poison.

Humans depend on oxygen to stay alive,

so it's hard to think of it as toxic.

Yet it can destroy delicate organic

molecules.

Oxygen gas produces earth's first mass

extinction.

Some of those ancient sulphur bacteria still

exist today, though they are banished to

areas that oxygen can't reach.

Extreme environments, like these volcanic

pools in Yellowstone National Park.

Two billion years ago, our last oxygen atom is

half of an O2 molecule again,

and with a new partner.

As a gas it wreaks havoc for most bacteria

alive at the time.

But this simple molecule is a new

opportunity for some.

Any life that tolerates O2 has a strong

advantage.

Breaking down organic molecules with O2

releases 16 times more energy than breaking

apart simple minerals.

This is a great success for these new bacteria.

They're still around today.

Millions of them inside every cell of our

bodies.

Called "mitochondria", they provide energy for

every complex life form.

Around 2 billion years ago life is hooked on

O2, and oxygen takes on a major role in shaping

evolution.

In 1909, paleontologist Charles Walcott is

working in the rocky mountains of British

Columbia.

All summer he's been collecting samples from

a rock formation called the Burgess Shale.

These rocks are ancient,

around 520 million years old,

so he isn't expecting more than a few small

simple fossils.

What he finds, and then keeps finding,

is astonishing.

Narrator: Most common among the fossils

Charles Walcott finds in the Burgess Shale is

an intricate creature he calls a "lace crab"

because it looks so delicate.

But how did something so complex evolve so

long ago?

It's possible that O2 played a part.

Oxygen levels in the atmosphere have varied

throughout history.

The lace crab's ancestors lived through

a time of low oxygen.

Life had just become dependent on O2 so this

was a disaster.

But lace crabs reveal how their ancestors

survived.

Their bodies are in segments and each

segment has a gill to absorb oxygen.

In evolutionary terms, it's simple to add new

segments and therefore increase the number of

gills, allowing the animal to absorb more O2.

When oxygen levels rise again, they thrive.

Walcott names this animal Marrella.

The rocks of the Burgess Shale exhibit a

rich diverse ocean teeming with animals

all as strange as Marrella.

And nearly all of them segmented.

Life now depends on O2.

Forced to adapt when oxygen levels fall,

and exploding into new forms when levels rise

again.

But 400 million years ago,

there's another drop in oxygen levels.

The animals that survive use a trick as

clever as Marrella's.

They find another source of O2.

Air.

There's always more oxygen in air than in

water, so finding a way to tap into oxygen

above the waterline is a clever move.

And it's what mudskippers do today.

When the amount of O2 in their swampy home

changes with the tide they head for land and

gulp air, pushing it against moist patches

in their mouths to soak up oxygen.

Breathing air means they can stay topside.

Mudskippers also breathe through their

skin but it has to stay wet to absorb oxygen.

Rolling in mud keeps their skin moist.

The returning tide brings oxygen-rich

water and predators.

Mudskippers need somewhere to hide so

they dig burrows.

But the oxygen-depleted incoming water doesn't

mix with the oxygen-rich water in

the burrow.

O2 levels could drop so low that the mudskipper

might suffocate.

These clever creatures have a solution.

They hollow out a chamber,

and fill it with air pulled in through their

mouth, one gulp at a time.

The air chamber is safe from predators and

holds enough oxygen to last until the tide

ebbs again.

Breathing air is a good way to survive low

oxygen levels in water.

When O2 levels rise again about 30 million

years later the first animals leave the water

to walk on land.

And they find a world rich with plants that

colonized the land long before they arrived.

Plants not only cover the land,

they have grown enormous with ferns the

size of trees.

There are so many plants they change the

atmosphere itself.

Countless large green leaves,

all pumping out oxygen gas for millions of

years.

These huge plants also lock up carbon in their

massive stems and roots.

Dead plants are buried so quickly in the

swampy forests they don't have time to rot.

All that carbon is locked away as coal.

Carbon reacts with oxygen to produce

carbon dioxide.

And since oxygen is always looking for a

partner, with so much carbon locked away,

oxygen levels can keep rising.

This is a great time for insects.

They breathe passively, letting oxygen diffuse

into their tissues through tiny tubes that

open down their sides.

The longer the tubes, the slower oxygen is to

reach their tissues and that limits the size of

insects.

But 300 million years ago,

O2 levels are almost double those of today.

Imagine a dragonfly with a 3-foot wingspan,

just one effect of so much oxygen in the

atmosphere.

And it's not only the animal world that's

supercharged by high oxygen levels.

There is something else.

The northern and southern lights.

They grace our skies in vivid color with the

help of oxygen.

High in the atmosphere, molecules of gas are

bombarded by charged particles from the sun,

giving them a flash of energy released again

as light.

If the charged particles strike

oxygen, the light show is a brilliant green.

When O2 made up 35% of the atmosphere,

the auroras must have been brighter and much

greener than they are today.

But this doesn't last.

270 million years ago O2 levels fall again to

just 12%.

So much carbon is buried that carbon

dioxide levels crash.

Plants need carbon dioxide to fuel

photosynthesis so there's much less

oxygen released into the atmosphere.

At the same time all of earth's continents are

fused into a single super-continent.

Cut off from moist ocean air,

a vast desert forms at the center.

It's the greatest catastrophe the planet

has known.

The Permian extinction.

90% of all species die.

Low oxygen is one of many causes that come

together to generate this crisis.

Yet life always adapts.

After the great extinction,

there are reptiles similar to modern

lizards.

They ambush their prey, running in sudden,

short bursts.

Like modern lizards, it can't run and breathe

at the same time.

As one front leg moves forward it squashes the

lung on the other side.

It has to stop to get its breath back.

Basilisk lizards have the same problem.

But they have a more efficient way to move.

Running just on its hind legs is faster and

doesn't squash its lungs.

It's a small improvement,

but if O2 levels plummet,

it could make all the difference.

230 million years ago, that advantage makes

one group very successful.

The first dinosaurs stood upright just as

O2 levels were at their lowest.

When oxygen levels rise again they are ready to

rule the world.

T-Rex lives at the end of the dinosaurs'

reign.

O2 levels then were lower than they are

today.

If T-Rex were around now,

it would be even more terrifying.

With a body tuned to lower oxygen levels,

today's higher oxygen levels would give T-Rex

a major boost.

Sophisticated dinosaurs like T-Rex did more

than just separate their arm movements

from their breathing.

They developed a new lung system.

Our lungs suck in air, remove the oxygen then

blow it out again.

But the T-Rex has rigid lungs.

Air sacs around the lungs suck in the air,

and the air is pumped through the lungs in

one direction only.

This is 33% more efficient than our way

of breathing.

Good thing T-Rex is not around today!

Narrator: Remember our oxygen atom?

The one forged in the heart of a dying star

billions of years ago?

It can't exist alone so it partners up and then

splits up.

But deep below these mountains in earth's

crust, this oxygen atom's first partner is

still trapped where it fell billions of years

ago.

The partner atom is locked inside a mineral

called corundum.

Corundum consists of just oxygen and

aluminum formed under heat and pressure in

molten magma.

But sometimes it gets contaminated by other

elements, like chromium,

creating the red stones we call rubies.

Within reach of the Himalayan Mountains,

rubies surface in the rivers after rainfall.

Downstream, ruby collectors are waiting.

Rubies have been collected for thousands

of years.

From long before we understood how they

were created, or that they trapped atoms of

oxygen from ancient times.

While the trapped atom remains in the ruby its

old partner, our last oxygen atom,

is on a much wilder adventure.

As part of a water molecule it's still

shaping life on earth.

We take water for granted,

but it's an extraordinary liquid.

Pond skaters can bend water,

creating dimples in the surface,

because the oxygen in the water molecules is

greedy for electrons.

Oxygen tries to pull negatively charged

electrons toward it, making the oxygen part

of the molecule slightly negative,

and the hydrogen part slightly positive.

Since opposites attract,

each water molecule is drawn into a dance with

its neighbor.

Underwater, all the forces cancel out.

At the surface, each water molecule is

pulled downward, creating a skin,

surface tension.

Strong enough for some animals to live their

entire lives here.

To avoid breaking the surface,

water skaters have legs covered in water

repellent hairs that need continuous

grooming.

For other animals the surface film is lethal.

Small insects are held fast by tiny electrical

charges on the countless water

molecules.

When the fly struggles, vibrations on the

surface give away its position to the pond

skater.

Surface tension is so strong it creates a

problem for creatures underwater.

A diving bell spider spins an underwater web

in the shape of a bell and fills it with air.

To top up the chamber, it must break through

the surface tension to get more oxygen.

Then, the spider sits in its own pocket of

air, waiting for prey.

The bell holds the spider rigid,

helping the bubble conserve oxygen.

When the pressure of oxygen in the bell

drops, more diffuses in from the water.

The bell is working like a gill but it

still needs the spider to top up the air

supply.

Some air-breathing creatures live in

fast-flowing streams where hightailing it to

the surface is a real effort.

And then there's this bug, aphelocheirus.

It doesn't need to reach the surface at all.

Like the spider, it's covered in an air bubble.

A bubble so thin we can see it only with an

electron microscope.

A cutaway section of the bug's body surface

shows thousands of tiny hairs that trap a thin

air layer so rigidly it can't collapse.

So oxygen in the water is always diffusing

into the bubble replacing that used by

the bug.

It's a true gill, covering a large part

of the bug's body.

These water creatures all owe their lives to

oxygen.

And in more ways than one.

Oxygen plays a crucial role in the formation

of ice.

As the temperature drops,

the dance of water molecules slows down

and they move closer together,

making the water more dense.

When it freezes the molecules arrange

themselves in a lattice and are farther apart

again.

So ice is less dense than water.

And it floats.

That's good for the animals living beneath.

Our oxygen atom is free again with yet another

partner.

But it's about to change once more as it

gets involved in reactions at the other

end of the temperature scale.

Narrator: Fire.

O2 combines with elements from hot fuel.

So much heat is released that electrons

in the fuel are catapulted into

different orbitals, then drop back,

releasing the energy as light,

the glowing flame.

Fire is yet another way that oxygen shaped life

on earth.

Humans have relied on fire for over a million

years.

When we moved out of Africa to colder

countries, it was vital.

It kept us warm and scared away predators.

And fire was a focus for humans to get

together, developing our social groups.

It even shaped how we look.

Cooked food is softer than raw food,

and is more nutritious.

Over time our jaws got smaller,

and our brains got bigger.

And we learned to use fire to transform the

world.

It might seem strange to set fire to the

forest that provides food.

But early hunters did just that.

Open glades supported more grass,

feeding more prey.

And hunting was easier with fewer trees in the

way.

Indigenous peoples cleared the ground for

crops with fire, leaving rich,

fertile soils.

And communities grew larger and more

elaborate on the back of farming.

Fire was part of the human toolkit.

That last atom from the burning star helped

people hunt, and went on to play a part in

the birth of civilization.

Dyeing fabric in exotic colors has a long

cultural history.

But one dye is stranger than most.

Cloth dyed in indigo comes out the same

color as it went in.

But hang it out to dry, and something strange

happens.

In water, the dye appears colorless as it

soaks into the cloth.

In air, the dye reacts with oxygen.

And after 10 minutes, the fabric changes

color.

A Babylonian stone tablet from 600bc

contains instructions for dyeing cloth with

indigo.

It stresses the importance of repeating

the dyeing and drying process many times to

get a deep color.

The process took a lot of effort and made

indigo fabric quite valuable.

Today equipment is different,

and designs are more ambitious.

But the real work is still done by oxygen.

For such a reactive element,

that original partner atom has led a quiet

life trapped in a ruby.

But not for much longer.

Thanks to an 18th century emperor.

Narrator: Precious and semi-precious stones

fascinate Austrian emperor Franz Stefan.

He relinquishes some of his vast collection in

the name of science.

Could diamonds be melted together to make

a huge priceless one?

He puts some small diamonds into a dish,

then uses a reflector and powerful magnifying

glass to focus heat where they touched.

Was this smoke a sign it was working?

No.

The smoke is carbon dioxide,

one carbon atom and 2 oxygen atoms,

released as the emperor vaporizes his diamonds.

Melting rubies would have been quite an

effort.

They must be heated to 4,000

degrees Fahrenheit to melt.

The most the emperor could do is free a few

atoms on the ruby's surface.

But the original partner atom is now

free at last thanks to the vaporized diamonds.

A few years later, in Paris,

Antoine Lavoisier understands the

mechanism of burning better than Franz

Stefan.

He realizes that oxygen is the gas responsible

for fire and the substance we need to

breathe.

Fire and breathing have a lot in common.

Both involve oxygen, release energy and

create carbon dioxide.

Respiration is just our body slowly burning

sugars.

It's a huge step forward for chemistry.

The Lavoisiers know that breathing O2 is

pleasant.

They couldn't have known they were

starting a trend.

In the 1990s a craze for oxygen bars starts

in Japan, and spreads to California.

Customers pay to breathe in 92% oxygen

for 20 minutes.

Combining the experience with

aromatherapy gives a choice of flavors of

oxygen.

Each jar contains an inconceivable number of

oxygen molecules: 10 with 22 zeroes after it.

So many that every jar is highly certain to

contain an oxygen atom breathed in by Genghis Khan.

The 800 years between us and Genghis Khan

seems like a long time, but to an oxygen atom

it's a mere blink.

Breathing in concentrated O2 is

thought to increase stamina and energy

levels.

Not surprising when you realize these people

are breathing in rocket fuel.

The space shuttle burns liquid hydrogen to

propel it into space.

To get the most energy, the hydrogen fuel is

burned with liquid oxygen.

Powerful but clean fuel,

generating only water as an end product.

Two minutes after takeoff, 28 miles up,

and the rockets are jettisoned.

But our last oxygen atom is in a molecule

that doesn't react with hydrogen.

Drifting in the upper atmosphere it's struck

by UV rays, and receives enough energy

to split apart and join a new O2 molecule.

The original partners are finally together

again.

This time as O3, ozone.

Ozone creates a shield, blocking lethal

radiation from the sun and protecting life

below.

The ozone layer first formed three billion

years ago as O2, made by the first plants,

rose high enough to intercept the sun's UV rays.

If life hadn't produced O2 early enough the

planet would have been uninhabitable,

bombarded by deadly ultraviolet rays.

This is the story of how life was made possible.

The story of the paradox that is oxygen.

Lethal, volatile and destructive.