Original subtitles

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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