All language subtitles for Earth s01e04.eng

The heavens. The great bowl of
the heavens, of our sky.

Just so beautiful!

I love the sky because, wherever
I am in the world, if I can find

some space, I can look up at this

big, blue, pristine space.

And I like the apparent permanence -
the fact that I can stare into

a sky that the dinosaurs stared
into, that Neanderthals stared into.

The atmosphere is essential for the
Earth to be habitable at all.

This thin layer of gas that
clings to our planet,

keeps liquid
water on the Earth's surface

and shields life from the most
harmful of the sun's rays.

As far as we know,
our thin blue line is unique

in the vast void of space...

..and today,
scientists are beginning to piece

together just how our planet
got its special blue bubble.

By going back to the Earth's
earliest origins,

we can now tell the almost
implausible story of our atmosphere.

How it emerged from
a toxic orange hell...

..and transformed the planet from
an exposed ball of rock...

..to a beautiful, living world...

..capable of nurturing
a staggering abundance of life.

This atmosphere has been
the planet's great protector

for 2.5 billion years,

soaking up everything
that our planet has thrown at it.

It's a thin, delicate,
fragile cloak that shields

and protects all life on Earth.

Our atmosphere is a unique
mix of gasses not found anywhere

else in the solar system,

gasses that allow Earth to be
a living, breathing world.

78% of our atmosphere is nitrogen,
which can be taken up by

bacteria in the soil and plants,
and it's an integral part of DNA.

21% of our atmosphere is oxygen.

It's there for animals to breathe,
but also for many living things

to use to convert
their food into energy.

Even less abundant gasses
are crucial for sustaining life.

A fraction of a percent is
water vapour, which condenses

and falls as rain,

and a tiny amount is carbon dioxide,

which might be a waste product
to us but it's absolutely

essential for plants
when it comes to photosynthesis.

It almost appears that this
unique cocktail of gasses

is here as a sort of
life-support system.

So, where did this beautiful
atmosphere come from

and how did it lead to the
origins of life here?

Well, to answer that, we need to
go back to the very beginning...

..4.6 billion years ago.

Our Earth began
as nothing more than dust and gas.

A nebulous cloud containing every
element our new world would need.

Over tens of millions of years,
the cloud begins to clump together,

forming rocks.

Pulled together by gravity...

..they grow bigger and bigger...

..until, finally, a new world
is formed.

Asteroids rain down
on the young Earth

for hundreds
of millions of years...

..its molten surface still searing
from the heat of its creation.

But something is missing.

The colour blue.

You see,
the Earth has no atmosphere.

The sun and the newly formed moon
sit in a jet-black sky.

This is how the Earth could
have remained...

..a lifeless ball of rock,
floating in the void of space.

This is what the
surface of the Earth may have

looked like 4 billion years ago.

Stark, brutal and yet,

in some ways, beautiful landscape.

The early Earth was little more
than a ball of cooling rock,

so where did the planet's
first atmosphere come from?

Now it might surprise you, but
I've got some clues to the answer

to that question in my pocket,

in the form of this tiny,

but extremely rare and valuable,
granular piece of rock.

This, you see, is a
carbonaceous chondrite meteorite,

and it was formed at the same
time our solar system was formed -

and I've got it in my hand!

I am holding the history
of our solar system

and the Earth in my hand.

4.5 billion years ago,
trillions of tonnes of this

type of material came together
to form our planet.

These meteorites are leftovers
from the Earth's creation.

So, through chemical analysis,

scientists can discover the raw
ingredients that made our world.

These meteorites contain
heavy elements, like iron,

and the rocky constituents
that formed the planet itself.

But chondrite meteorites contain
lighter elements too.

Chemical analysis reveals that
these rocks contain carbon,

hydrogen and sulphur,

and we can still see them
belching as gasses

from volcanic
vents around the world today.

When combined, these elements
form new compounds like methane,

carbon dioxide and
hydrogen sulphide,

which are light
enough to exist as gasses

but not so light they
drift off into space.

So, meteorites like this
weren't just the

building blocks of our planet -

they contained the essential
ingredients for its atmosphere.

And 4.5 billion years ago,

that had begun to change everything.

The ancient Earth holds within it

everything it needs to create
the first atmosphere.

Those ingredients just have
to make it to the surface.

But deep within the young
Earth, something is stirring.

Across the globe,
molten magma races up from within...

..and these rivers of liquid fire
unleash gasses that will

transform our planet.

The world is smothered by a thick
toxic fog.

As the sun creeps above the horizon,

gas scatters the light.

Earth gets its first colour-filled
sunrise.

This new world now
has an atmosphere...

..but one like nothing
we've ever seen.

We're all familiar with the colours
in the early-morning sky,

but a sunrise 4 billion years ago
would have been very different.

Sunlight passing through that
churning mixture of methane

and carbon dioxide would have given
the whole planet an orange hue.

But this toxic atmosphere
was very important.

It was the first time
that our planet had

a protective shield from space.

But, of course,
it was still a very alien world -

would have been to us - and not just
because of that noxious

orange fog, or the searing, hot,
black, bare volcanic rocks

beneath our feet.

It was because something
fundamental,

something that we take for granted
every day, was missing.

Water.

Today, 70% of the Earth's surface
is covered in water.

A planet of
almost limitless blue...

..with endless rivers...

..freezing ice caps...

..and turquoise tropical paradises.

But 4.5 billion years ago...

..there wasn't a single
drop of liquid water

on the ancient Earth's surface.

However,
the planet wasn't totally dry.

The young atmosphere
did contain water.

Asteroids and volcanic eruptions
have released a vast

ocean of water vapour.

Trillions of droplets
were floating in the sky...

..so small they soar
on moving air.

Colliding and merging
with each other, they slowly grow...

..until they can no longer
fight Earth's gravity.

En masse, they are pulled downwards,
towards the ground.

But with the atmosphere still
scorchingly hot from heat

trapped by Earth's formation...

..not a single drop of rain...

..has ever made it to the surface.

And it's been the same story every
day for tens of millions of years.

The Earth is stuck -
a barren desert world

totally incapable
of supporting life.

Water today is on a continual
journey.

It emerges from the leaves
of green plants as vapour,

rises up to the sky,
where it forms clouds,

which then condense into rain,

which falls onto the ground,
which drains into the rivers,

which eventually flow into
our vast oceans.

And we're very used to seeing water
appear out of our atmosphere.

What about those lovely soft layers
of mist that we see over rivers,

or the dew on your toes
if you scuff across a summer lawn,

or when it falls as rain or snow?

The only reason our planet is
a water world is because it's the

right temperature and pressure for
water to form out of the atmosphere.

4.4 billion years ago,
Earth needed to cool down.

Slowly, heat has been radiating
out into space...

..over millions and millions
of years.

Until...

..a tipping point is reached.

What starts with just a few drops

becomes the greatest deluge

the solar system has ever seen.

Huge weather systems
sweep across the planet

and storms which last centuries dump
oceans of water from the skies.

A key element in the equation
of life had been

well and truly unleashed.

Our planet is transformed.

As the Earth continued to cool,
the rains that fell from its thick,

dense atmosphere created a new
water world.

And for the first
time in its history,

it would have looked
a little bit like this.

If you gazed into the sky,
you would have seen clouds,

you would have felt the wind
and the rain on your face.

And if you listened,

you'd have heard waves
carving a new coastline.

But that's where the similarities
would have ended,

because this rocky,
wet world was devoid of life.

But it was a world
where life could begin.

Water was the crucial ingredient.

Not long after Earth's oceans
rained from the sky,

a shallow pool was about to
play host to the most important

moment in the history of the Earth.

So much of how life began
is still a mystery.

It's not known exactly
when, where or how it happened.

But we do know that,
one day on Earth,

a living thing
came into existence.

The first microscopic organism.

And in that instant of pure chance,
everything changed.

The Earth became a living world.

All trace of the first life has
vanished, lost to history.

But even today,

we can get clues as to what
early life might have been like.

High in the Andes is one of the
largest geyser fields in the world.

The water in this vent is
boiling at 85 degrees Centigrade

and NASA scientists have
looked into this water and found

that it contains one of the highest
concentrations of arsenic,

a serious toxin,
anywhere in the world.

And these toxic conditions
are similar to those

found on the early Earth.

But amongst the poison
and boiling water,

something ancient is flourishing.

Just look at all of these
beautiful colours here.

That's life - a primordial mat
of billions of thriving bacteria.

These hardy bacteria are called
extremophiles and, just

like their predecessors, they've
adapted to live in this hot water.

In fact, they've carved out a niche
where they can proliferate.

There are a great range of species
here and an enormous

number of individual organisms.

Which just goes to show that
even the simplest life is inherently

flexible, adaptable and tough.

So, perhaps it's not surprising
that that early life grabbed

an opportunity to try and live
in an environment which, for us,

is incredibly harsh and hostile,

but where they could prosper.

Today, life is prolific.

It thrives in the most
unlikely of places across the world.

But living in these extreme
environments comes

with severe limitations.

The extremophile bacteria
living around these

hot springs are essentially
locked in,

defined by the very precise
requirements in terms of the

heat of the water and the nutrients
in it. And if we were to remove

them from this highly specialised
environment, they would likely die.

And things were pretty much
the same for early life on Earth.

It was essentially stuck, trapped
in the niches that it evolved to

survive in. And because all
of the nutrients were in the water,

the option for life on land
simply wasn't there.

Early life wasn't prolific,
widespread, or even visible.

The ancient Earth is harsh
and unforgiving...

..with barren black land...

..and acidic green oceans.

But the biggest barrier to life's
flourishing is the atmosphere,

toxic and orange.

An atmosphere in constant turmoil.

Tectonic movements in the Earth's
crust drives land formation,

which in turn creates massive
atmospheric instability.

Vicious winds sweep dust
high up into the air...

..and these dust particles
create more clouds.

Storms rage across the planet,
laced with poisonous gasses...

..deadly to the vast majority
of life we know today.

But whilst chaos rages
above the waves, deep underwater

our ancestors are simply existing,

seemingly trapped...

..with no means of escape...

..day after day,
for nearly a billion years

where nothing appears to happen.

Today, life is no longer
confined to the water.

Oh, yes, what a view!

Both life and the atmosphere
that supports it have undergone

an astonishing transformation.

It's a male.

It's got the comb on top of its head
and its feathers are all silvery,

rippling in the wind as it glides
along the edge of this escarpment.

With a wingspan of more than 3m,

the giant Andean condor is
one of the largest birds on Earth.

Oh, goodness me! Look at that!

Absolutely sensational.
Now I can see its eye.

I'm looking into the eye
of an Andean condor.

Oh!

It's ornithological nirvana!

Watching these giant birds
soaring here

just reveals how their life
is completely intertwined with

that thin cloak of air that's
wrapped around our planet.

But then, when you think about it,
everything - every plant,

fungi, every bacteria, every tiny
insect, every giant reptile,

even us - are completely
dependent on this atmosphere.

So, how DID the atmosphere
go from a toxic orange haze to the

nurturing cocktail of gasses
we know today?

Well, it was life itself that would
make the difference...

..thanks to a giant
evolutionary leap.

The development of complex life
was far from inevitable.

When you think about it,

there are plenty of forks
in the road of evolution,

trillions of dead ends

and there is no definitive
end point.

But the very fact that we exist
proves that whatever card

is thrown at life,
it plays it and it survives.

And that's precisely

what was happening 3.5 billion years
ago.

Life was playing its card - slowly
evolving, gently proliferating -

and it wasn't quite as stuck as
we might have thought it was.

In fact, a significant development
in a single cell was about to

change the way that life
could exist.

Life was about to take
a quantum leap forward.

A leap, that would
change our atmosphere forever.

It started with a mutation
that altered the fundamental

chemistry of the cells...

..giving them the ability
to capture the sun's rays...

..and store the energy as glucose,

energy the cells can then use
to grow and reproduce.

This was photosynthesis...

..an evolutionary
innovation that will change

the course of Earth's
history forever.

The ancestors of this
cell are still around today.

They can be found in almost
every puddle, lake,

sea or ocean across our planet.

Peering down through this microscope
is like taking a look

back at life on Earth
almost 3.5 billion years ago.

You see, these rod-shaped structures
here are cyanobacteria,

and we think they're pretty similar
to those that existed

trillions of generations ago, when
our atmosphere was very different.

Now, they may not look impressive,
but I've got to tell you,

they're probably one of the most
successful organisms to ever live.

A little over 3 billion years ago,
these tiny flecks,

these microscopic organisms

just a fraction of a millimetre
across, started to build

an atmosphere which humans
could live and breathe in.

Thanks to energy from the sun,
these cells are able to steal

hydrogen from water molecules and
combine it with the carbon dioxide

dissolved in the oceans, fabricating
essential tools for life.

Individually,
these revolutionary cells,

which you can still find in
water bodies like this all across

the planet, produced a negligible,

unremarkable, nonexistent effect.

But when they combined
in their trillions,

when they combined en masse,
they were about to demonstrate,

for the very first time, the awesome
power of life on Earth,

and that would have a profound,
long-lasting

physical resonance on our planet.

Life powered by photosynthesis
thrived.

Cells with this new ability to
harness energy from the sun

out-competed those that couldn't.

So, they began to multiply.

One becomes two.

Two become four.

Until there are literally
trillions of offspring.

Enough to fundamentally change
the chemistry of our world.

Photosynthesis was a game-changer
for life because the

ingredients that it required were
so readily available and abundant.

But the by-products of many types
of photosynthesis include a very

reactive and dangerous gas.

Now, for these revolutionary
early organisms,

this was just a waste product,
something to be thrown away.

But for the likes of you and I,

and the rest of complex life
on Earth, it's absolutely essential.

I'm talking, of course,
about oxygen.

Trillions of bacteria are spread
across the ancient oceans...

..and the waste oxygen they
throw away is enough to build a new

atmosphere for our planet.

Bubbles of oxygen race upwards,
towards the surface.

But they can't escape.

The bubbles are absorbed and vanish.

Earth seems trapped,
with a toxic atmosphere of methane

and carbon dioxide.

The Earth was essentially in stasis.

You see, that toxic orange
atmosphere still enveloped

the planet.

Life was still microscopic
and could only exist in the oceans,

and there was no
oxygen in the atmosphere.

To all intents and purposes,
you could say, well,

that the planet was stuck.

But that was about to change.

Because it wasn't just oxygen
dissolved in the water -

there were metals, too...

..including iron.

The iron, like oxygen, is invisible

to us when it's dissolved in water.

But we all know what
happens when iron,

oxygen and water come together...

..and there's plenty
of evidence of that on this old bus.

Just look here - this lovely brown,

orange and red.

Rust.

The iron is being oxidised -
aggressively attacked

by the oxygen in the
presence of water, or water vapour.

But what's interesting
is that, whilst the iron

and whilst the oxygen are soluble
in water,

the rust is not.

The newly released oxygen reacts

with the dissolved iron
already present

in the oceans,

and that causes
something extraordinary to happen.

Rust pours onto the ocean floor.

The world's oceans turn red.

And if you know where to look,
you can

still find evidence for this
bizarre effect.

I'm armed with a rock hammer.

If I have a little tap at this
stone, there we are.

Let's have a look at what's inside.

This rock once formed
part of an ancient seafloor.

Hm, look at that.

You see that there, that red?

That's iron

laid down billions of years ago,

a volatile memory of oxygen reacting

with iron in the early seas.

A sort of geological tattoo.

I love that.

This rust was to have
a profound effect

on our Earth's young atmosphere.

For half a billion years, oxygen
has been trapped in the oceans.

But now, iron has almost been
totally flushed from the seas.

At last, the oxygen in the water
has nothing else to react with.

It can break free.

Over millions years,
oxygen flooded from the oceans...

..and our atmosphere
was transformed.

When those bubbles first breached
the surface of the ocean,

you might have thought that
the atmosphere was getting

a breath of fresh air,
and to some extent it was.

But this wasn't the moment
when life suddenly flourished,

or when it developed that complete
and utter dependence that

contemporary complex life
has upon oxygen.

But that's not to say that
when those bubbles first fizzed

out there that this
wasn't a momentous moment.

It was.

The planet was about
to be re-calibrated,

and the relationship
between the ocean,

the land and the atmosphere
was going to change forever.

And as this volatile, reactive gas
flooded into the atmosphere, the

full destructive force of oxygen was
felt across the planet's surface.

Oxygen attacks the Earth.

Any rocks containing iron
and aluminium rust and crumble,

driving vast dust storms.

The world is being torn
apart by its own atmosphere...

..and this has a startling
side-effect -

the entire Earth turns a vivid red.

Scientists find evidence for this
red Earth in

rock formations in landscapes
all over the world.

Direct evidence of the action
of all of those

trillions of cyanobacteria
churning out oxygen.

And before oxygen, the planet
was barren, grey and black.

You see, it's oxidation that
gives us this wonderful red hue.

But oxygen's effect on the land
went further.

You see, oxygen doesn't just
react with iron -

it reacts with pretty much anything.

It attacks minerals within
the Earth's crust...

..creating as many as 3,000
exotic new minerals,

all previously unknown
to the solar system.

Minerals that led to an explosion
of colour right across the planet.

Minerals that, to this day,

play a vital role in sustaining
the rich complexity of life we know.

Now, one of the colours
unleashed by oxygen is this rather

wonderful sea green here.

You see, when copper, the metal,

comes into contact with
oxygen in the air, it oxidises,

producing this - copper oxide.

And it turns out that this compound

was fundamentally important
in the development of more complex

life. And what's more, it retains
its biological importance today.

It's necessary for the synthesis
of neurotransmitters in our brains,

and the brains of other animals,

and also for the production
of hormones and pigments.

So, even in today's world,

life is dependent on that chemical
complexity that was unlocked

so long ago, when our atmosphere
became richer in oxygen.

Thanks to oxygen, we live
in a world of extraordinary colour

and diversity.

A myriad of minerals
colours the Earth's surface...

..and the biological world
has continued

to make use of this
ever-increasing

chemical complexity to transform
the planet.

From the rich green
carpet of plant life...

SHUTTER CLICKS

..to the fluorescent
pink feathers of flamingos.

Oxygen has allowed life to
flourish in ways unimaginable

3 billion years ago.

But this volatile gas had
one more gift to bestow.

As oxygen enriches the atmosphere,
it reacts with methane,

stripping it away.

And as methane levels drop,
the orange haze lifts.

Nitrogen and oxygen
in the atmosphere are left

to scatter the light.

The colour begins to change.

For the first time in Earth's
history, the sky

is an oxygen-rich, brilliant blue.

Today, this lovely thin blue line
marks our Earth as unique

in the entire known universe.

It's a spectacular
demonstration of a 4 billion-year

dance between our atmosphere
and life -

an atmosphere that was

created, shaped
and calibrated by life itself.

Our planet went from volatile,
fiery and dead to the beautiful

living and breathing blue bubble

floating in the darkness of space.

How do scientists unravel billions
of years of our planet's history?

In this episode, we saw how
meteorites -

rocks that have fallen from space -

can tell us what Earth's
early atmosphere was made from.

This is a chondrite meteorite.

4.567 billion years old -

the oldest thing you could hold
in your hand -

and it's made of all these
tiny droplets

that were part of the
earliest solar nebula, including

all the gasses that eventually would
wind up in the atmosphere.

Meteorites are
so valuable to science

that researchers go to great
lengths to track them down.

In 2020, scientists from the
University of Manchester set out

on a nine-week expedition to one of
the most remote areas of Antarctica.

Meteorite hunters
go into the depths of Antarctica,

into the extremes of the cold,
near the South Pole, because

they can find so many meteorites
in one expedition, because the

meteorites show up so well
on the white ice...

..compared to, say, other
places where the meteorites are

very hard to spot from normal rocks.

Studying meteorites has
helped answer some of the most

fundamental questions
about our planet.

So, the question of where
the water on Earth came from

and when it arrived is really
central to everything.

Some water was present in the
material that formed our planet,

but that's not the whole story.

We think that one of the other
ways that the Earth got its water

is through meteorites.

So, these meteorites would have
had water locked into their rocks,

or perhaps even on their surface,
as frozen, in outer space.

And then, the water would
have been degassed

into our atmosphere
as water vapour.

Later on,
when the Earth cooled even further,

that atmosphere would have condensed

and the water vapour would have then
formed liquid water on our surface.

Scientists think it's only after
the arrival of water that life

was able to get started.

The origin of life is one of the
greatest questions in science and

it's fair to say that we don't know
when, where or how life started.

A shallow rock pool is
one of the leading theories.

People think that shallow pools
would have been a potentially

important site for the origin
of life because they can get

wet and dry over and over again.

Through this repeated
cycling of wetting and drying,

re-flooding and evaporating,
maybe through a tide, maybe through

seasonal variation, more
and more complex molecules can form.

And that process could have been
the precursors for things like DNA,

which is what makes up
the information in our cells today.

But there are other theories.

Some scientists think life began
in a deep-sea hydrothermal vent.

Hydrothermal vents
are sources of gases,

like hydrogen sulphide for example,
and provide

the kind of reactive conditions to
make the building blocks of life.

Others think that life originated
somewhere completely else -

not on the Earth at all -
and landed here on a meteorite.

All of these different theories
have sort of different details,

but the punch line is that
life needed water

and it needed a way
to harness energy.

Although life's
origins are still debated,

scientists have some idea
when it happened.

This is one of the clear-cut
examples that life was living

even 3 billion years ago.

This is a formation called
a stromatolite.

What you're looking at shows
a structure

created by a lot of microorganisms,
single-celled organisms.

And as they grow and they reach
for the light, they secrete various

gluey substances that glue together
bits of sand in the environment,

and that actually helps keep
it from dispersing and blowing away.

They are astounding in that they
have the ability to adapt to

environmental change
and to change the environment

because they can be so abundant.

These fossilised structures were
created by cyanobacteria

and millions of them
can still be found along the coast

of Western Australia.

Cyanobacteria might not seem
so impressive,

but they're probably
one of the most influential

and successful organisms
ever to appear on planet Earth.

They were the organisms that
invented this ability to

break water into oxygen and hydrogen

and spit out that oxygen.

That oxygen was able to get
released into our atmosphere.

They completely
transformed the world.

There are these moments
in the history of life that seem to

have only happened once.

Oxygen producing photosynthesis
is one of them.

Was it a freak accident?
We just don't know.

The evolution of our atmosphere is,
in many respects,

the story of the evolution
of life on our planet.

Life can change a planet
fundamentally.

But it's always this
cause-and-effect kind of dance

between the environment
changing life

and life changing the environment.

The story of our changing
atmosphere is not over.

It will continue to evolve
both naturally

and under the influence of human
activity.

If we don't understand
the history of the atmosphere,

how can we possibly be the stewards
of the atmosphere moving forward?

By understanding the huge

and complex steps it took to
develop our atmosphere, hopefully

we can develop approaches to take
care of it for generations to come.

Next time...

..the making of the modern world.

How the end of the dinosaurs...

..through cataclysm and chaos,

set the stage for a human planet...

..to take its place.

If the Earth could talk,
what would it tell us?

Well, the Open University imagine
how it might answer

some of our questions.

To experience this interactive
presentation, go to the

website on the screen and follow
the links to the Open University.

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