Original subtitles

Just look at that.

It's awesome, isn't it? If not a little terrifying.

A massive tsunami of ice, cascading down the valley.

Try to imagine that, though, not just happening here,

but happening all over the world.

Well, 700 million years ago...

..that's exactly what did happen.

Ferocious forces...

..created a climate emergency.

And from pole to pole, across all of the lands and oceans...

..our world...

..froze.

The story of this extraordinary time is written in the rocks,

and as the latest evidence helps us piece together what happened...

..we know this disaster hit at the worst possible time.

Just as the earliest forms of animal life were evolving, the ice

threatened to destroy them, and the world as we know it, forever.

The thing is, this moment in our planet's history is also

a story of resilience, because this climatic

and environmental catastrophe lead to something miraculous.

You see, this new life on Earth didn't just survive the ice

and its aftermath, it thrived.

The deep freeze saw a new age on Earth,

an age of complex life,

of a greater size and diversity than ever seen before.

Life that would go on to dominate the oceans

and the land to this very day.

Our story begins in Earth's ancient past...

..850 million years ago...

..when the face of our planet was unrecognisable.

Almost all the land that existed was gathered into one,

giant continent, called Rodinia.

Thousands of kilometres, coast to coast,

this rocky landmass dominates the planet.

For all its scale, from its jagged peaks...

..across its desolate plains...

..there are no plants

and no animals.

But there is life here.

In shallow, coastal waters...

..bacteria clump together

into living mats that cover the seafloor.

For nearly three billion years, this has been the limit of life on Earth.

A planet that couldn't be more different from the world we live in.

Even in Iceland, with its harsh winters, so hostile to life...

..once the warmth returns, so do a host of plants and animals.

It's honestly hard to imagine that up until very recently,

this was a dark, desolate and frigid place, because now look at it.

It's bright, it's busy, it's warm, it's busy with life doing

what it needs to do at this time of year, which is flower and fruit.

And look at this lovely, delicate little harebell here.

And these are the fruits of the crowberry.

And they're meant to be edible.

Best left for the birds.

But aside from the taste, look at that, it's a perfect little package.

It's exquisite. But what interests me more, what's more incredible,

more important, is how this fits into the grander scheme of things.

All the life here has evolved in partnership

with everything around it.

Each individual is just one strand in an intricate web of life.

Every part connected to, and reliant upon, all the others to survive.

Large, complex life in the modern world can only really make it

if it's part of a bigger, interconnected ecosystem, like

this one here, an ecosystem which is as complex as the life it supports.

But the staggering thing is, the truly staggering thing is,

that until recently, none of this existed.

You see, for over four billion years,

that's pretty much our entire planet's existence, large,

intricate life like this was nowhere to be found.

All the animal life that now exists in the world can

trace its origin back to what was happening off the shores

of Rodinia, 850 million years ago.

In the coastal waters, amongst the bacteria,

something new has appeared.

Giant cells tower over the living mats.

These strange microbes are the distant ancestors of animal life.

They're not bacteria, but eukaryotes - bigger,

more complicated...

..the first cells with a nucleus.

The bacterial mats here get their energy from sunlight, but like

you and me, they eukaryotes rely on food from their surroundings.

And in this basic ecosystem, there were slim pickings,

bacteria floating in the water,

and the slow flow of minerals from the eroding land.

Enough to survive,

but far from what they need to thrive.

These new life forms seem destined to live out a meagre existence

stuck on the sidelines...

..never able to evolve into the vibrant ecosystems of today.

But the planet was about to deliver a colossal shock to the system...

..thanks to powerful forces that are still at work today...

..and can be witnessed in places like Thingvellir,

on the western coast of Iceland.

Walking through here, I get a real sense of raw, primal,

brutal forces at play, and those forces certainly are at play.

You see, every year,

the walls of this chasm move apart by one centimetre.

Now, I know it doesn't sound like much, but that's

because we've got to start thinking about this in geological time,

so that's hundreds of millions of years, not hundreds of years.

The rock beneath my feet is quite literally splitting in two,

along a fracture which runs for thousands of kilometres.

Iceland sits on a boundary between two giant

chunks of the Earth's crust,

known as tectonic plates.

Heat churning within the mantle of our planet

is driving these plates apart.

As they spread...

..the land above stretches

and then tears...

..creating great rifts through the landscape.

These forces have been moving the world's greatest landmasses,

creating and destroying them, for more than three billion years, and

nothing can resist them, not even a giant supercontinent like Rodinia.

Deep beneath Rodinia...

..swirling currents of heat cause tectonic plates to shift.

They begin to move apart...

..and great chasms gape open across the landscape.

This great continent is ripping itself apart.

Earth is the only planet in the solar system to have active

tectonic plates.

And they're constantly reshaping our world and its life.

In many ways, we can think of the history of our Earth

as about the interplay between life and geology,

and sometimes, the great planetary process have given life

a bit of a leg up.

On others, they've knocked it right back down again.

One of these moments was about to play out,

and what happened next would ultimately define the entire

living world that we experience today.

As the rifting continues for millions of years...

..it creates deep valleys...

..powerful rivers...

..and hundreds of kilometres of new coastline...

..all greatly increasing erosion,

and causing a flood of minerals to pour from the land into the oceans.

Thanks to this boost in minerals, the eukaryote population explodes.

They build numerous colonies,

a crucial step towards forming multi-celled animals.

And some organisms now have enough energy

to produce protective spikes...

..built from all those minerals washed off the land...

..and vital defences,

as there were now predators taking advantage of the boom in numbers...

..in this newly energised ecosystem.

We've witnessed this dramatic change with our own eyes,

thank to recent discoveries made

in 700 million year-old rocks from the Grand Canyon.

Scientists have discovered these...

..tiny micro-fossils of marine life, each smaller than a grain of sand.

What shocked them were the holes in the outer shell,

most likely created when they were attacked and eaten.

Now, the predators weren't preserved,

but the best guess is that they were something like...

..this...

..a single celled amoeba called Vampyrella.

This predator punches holes in its victims

before sucking out their inners...

..leaving behind holes near identical

to those found on the micro-fossils.

This is the earliest evidence of predators and prey ever found.

That element of everyday life, so key to our modern world.

The vast tectonic processes at work provided complex life with

the spark that it needed,

an environmental revolution which allowed it to move towards

the interconnected ecosystems that we see around us today.

But just as life was taking this great leap forwards,

disaster struck.

The forces tearing the ancient supercontinent apart were about

to plunge the entire world into a seemingly endless, desolate winter.

On Rodinia, events take a catastrophic turn for the worse.

Superheated magma bursts through the surface,

as rifting thins the crust in multiple places.

Molten rock swamps two million square kilometres

of the continent...

..one of the largest outpourings in Earth's history.

The lava cools and forms the dark rock basalt...

..creating a vast black stain across the heart of the continent.

You see, the great freeze begins not with ice...

..but with fire.

Fresh basalt is quite incredible stuff.

This is about ten months old.

Now, it's not terribly easy to walk over, and you certainly

wouldn't want to stumble.

It's extremely jagged, ripping your boots to pieces,

and you wouldn't want to fall on that, would you?

But what's really incredible about this rock is that it has

the capacity to change our planet's atmosphere.

As rain forms, it absorbs carbon dioxide gas from that atmosphere.

When that rain flows over basalt, there's a chemical reaction

that draws carbon dioxide out of the water

and binds it to the surface of the rock, locking it away.

We know that carbon dioxide is a very potent greenhouse gas,

has the capacity to lock lots of heat into our atmosphere,

and the more of it that we pump into the air,

the more we see our global temperatures rising.

But then, I don't need to tell you about global warming.

What's interesting is that the reverse is also true.

If we take carbon dioxide out of the atmosphere, temperatures fall.

The erosion of millions upon millions of tons of basalt,

spewed up when Rodinia broke apart, sucked that warming

blanket of carbon dioxide out of the atmosphere.

And it flicked the Earth's thermostat

from a comfortable stasis to chill.

Falling levels of carbon dioxide...

..pushed down temperatures...

..awakening a sinister force.

Ice...

..something not seen here on the planet for a billion years.

For now, it's limited to the poles.

But it's spreading.

Whether you're a microscopic or more human-sized,

most life loves the warmth...

..especially here in Iceland, where the winters are so harsh.

Summers here are truly amazing - look how verdant, how green,

how lush it is.

And there's also a tremendous diversity of plants -

flowers, mosses, dwarf trees.

And, of course, on a day like today, blue sky, sunshine - it's lovely.

But the lingering cold of winter is never too far away.

Venture up into that lingering cold...

..and it's possible to see how life suffers as temperatures fall.

I've only travelled about a mile, but I've climbed in altitude,

and the difference in the landscape is really rather stark.

Look at it.

It's principally barren rock

and the plants here are scattered few and far between.

You see, up here, the temperature only

gets above five degrees Centigrade for a few weeks of the year,

and when the temperature drops below that,

plants can't produce structural tissues.

You can give them all the water, all the nutrients they want,

but at lower temperatures, they just can't build their own bodies.

Across the world, whenever temperatures drop low enough,

for long enough,

plants and life slowly fade away.

Temperature is the natural limiter for complex life in our world,

and those rich, interconnected ecosystems,

which can thrive down there can't even survive up here.

When it gets cold, the web of life unravels.

On the ancient Earth, as temperatures continue to fall,

the cold advances on early life from all sides.

Armadas of sea ice march out from the North and South Poles...

..as on land, immense glaciers surge forth from the mountains.

The places life can hold on are rapidly shrinking.

The ancient Earth teeters on the edge of a climate catastrophe,

as the ice tightens its grip.

Today, ice covers a tenth of all the land on the planet.

Vast sheets blanket the poles...

..and the high mountains of all of the continents.

Nearly 10% of Iceland is covered by a single sheet of ice.

The icecap here is vast.

It stretches for 100km in that direction.

It's 140km wide and nearly a kilometre thick in some places.

But in the modern world, ice is limited.

It comes to a grinding stop down there.

And that's not just because of human-induced climate change.

The world is simply too warm.

The idea that ice could smother the whole world

seems incomprehensible.

But just over 710 million years ago,

the Earth was a much more vulnerable place,

and when the ice started marching, there was very little to stop it.

We now know just how far it reached.

Look under the leading edge of this icecap

and you can see the evidence of its raw power in the countless

chunks of rock ripped up and dumped by the ice.

Glaciers are so destructive, they leave scars in the rock record.

Like these stones and boulders,

a completely different type or rock to the layers around them.

Called drop stones, the flowing ice picked them up and dropped them

hundreds of kilometres from where they originated.

Scientists have found these in rock layers that were sat over

the equator 700 million years ago...

..hinting at an event of an astonishing scale and reach.

The ice is winning.

A band of warmth still holds out around the equator...

..the last refuge for life.

But as the white expanse spreads,

more and more heat is reflected back into space...

..and the freeze becomes a runaway process.

Ice surges over almost all of the remaining oceans.

Even at the equator, hope slowly fades.

And finally, this last stretch succumbs...

..leaving the planet a frozen, white marble...

..floating in the darkness of space.

Ice had claimed the world...

..in an event known as Snowball Earth.

It's almost impossible to imagine,

but pretty much all of the planet was just like this.

The whole world was plunged into a deep Ice Age, wrapped in sheets

of ice sometimes kilometres thick, choking our land and our oceans.

It was a global winter with no end in sight.

Modelling suggests that it was

minus 70 degrees Centigrade at the poles...

..that it never got above freezing anywhere on the planet.

It would have been pretty sterile.

It would have stressed or stalled the water cycle.

There would have been little or no evaporation...

..hence no rain,

no snow,

very few clouds.

If there were clouds, some would have been clouds of carbon dioxide.

This was an incredibly hostile place.

It couldn't have been more different than the beautiful, vibrant,

dynamic planet that we have today.

The triumph of the ice is a disaster for life.

The ocean is almost entirely cut off from the atmosphere.

It's dark, cold.

And the flow of minerals from the land slows to a trickle.

The food web begins to fall apart.

And the predecessors of animal life...

..falter.

A mass dying is under way.

This was no short cold snap life could easily ride out.

OK, the ice would have waxed and waned a little,

with the changing of the seasons, but the cold persisted,

unending, for millions upon millions of years,

with no hope of release.

I know it looks like a massive, muddy field,

but I'm actually walking on top of a glacier, albeit a dirty one.

And out here, in the biting face of the cold, it's easy to

imagine that the endless winter put pay to complex life on Earth.

But of course, it didn't. Live survived.

You and I are living, breathing proof of that.

But when it comes to looking for the clues that might tell us

how it pulled off its great survival trick, these wild,

frozen places are a top place to look.

You see, even on the exposed top of the glacier, it's possible

to find chinks in the ice's armour,

just big enough for life to exploit.

Here we are. This is what we're looking for.

This, we think,

is very similar to what might have formed way back then.

Some dust blew out onto the glacier, was warmed up by the sun,

it melted the surface of the ice and formed this puddle.

They're called cryoconites, and it's this simple combination of dust

and water which proved to be life's saviour.

Now, I know it doesn't look like much, but this is, in fact,

a beautiful little oasis out here on top of this vast glacier.

Yes, in this one small pool of water, there's abundant

minerals from the dust, and plenty of exposure to the air and sunlight.

As astonishing as it sounds,

that means it's possible to find life

in muddy puddles like this.

The simplest would be single celled algae and bacteria,

but there are others.

These are images that have come from an actual cryoconite.

You've got things like this rotifer here,

and here, our favourite little water bear, the tardigrade.

And they would be feeding on those smaller organisms.

And, all together, a soup here of different animals

and plants in a simple food web.

Now, I've got to tell you, I've seen life in some pretty amazing

places in my time, but the idea that there could be a functional

ecosystem living in a puddle, on top of Europe's largest glacier?

Well, that is quite extraordinary.

It's thought that during Snowball Earth, there would have been

enough patches of exposed rock and land to generate dust.

Not as much dirt as this, but enough to create many similar puddles.

And, what's more, scientists have exposed these tiny oases

in the laboratory to conditions found on Snowball Earth...

..and the life inside survived.

For no less than 50 million years, 50 million years, that's

a long time, life clung on in such places throughout the deep freeze.

Let's be clear, this was a tough place to exist,

but if life wanted to do more than survive, if it wanted to

flourish, then the Earth would have to escape its icy prison.

There was no easy route out.

The ice prevented almost any change on the planet...

..with one exception.

Even an endless winter can't stop the planet creating volcanoes.

Each eruption punching through the planet's frozen shell.

Ever since our planet first formed,

the heat in its mantle has fuelled volcanoes.

Today, there are over 1,000 active across the world.

And there would have been at least as many during Snowball Earth.

But even the ferocious heat of all that molten rock was too

fleeting to break the grip of the global Ice Age.

What did offer a slim chance of escape was something else.

Something invisible that came with each eruption.

As each eruption tore through the ice,

it released a great slug of volcanic gases,

including the carbon dioxide stripped from the atmosphere

all those years ago.

With the land and ocean covered in ice, there's nothing to stop

the slow build up of this powerful greenhouse gas.

And it begins to finally bring some warmth to the frozen planet.

The world stood on a knife edge.

If enough carbon dioxide could build up, there was

a chance of breaking the freeze.

What would finally decide the planet's fate is a process

we're all too familiar with today.

This glacier has been melting for the last 130 years,

and the evidence of that melt is all around us.

Look at this vast, glacial lagoon here, full of bergs

and brash ice, and there's meltwater draining out into the sea.

This is global warming.

And the key thing is that this

process has accelerated in the last 30 years.

You see, just as freezing is a runaway process, so too is melting.

Rising temperatures drive more water vapour into the atmosphere.

It has a powerful greenhouse effect.

And, as ice melts,

the exposed dark surfaces absorb yet more warmth from the sun.

Changes like these feed into each other

and create tipping points, beyond which warming becomes explosive.

To limit climate change today,

we must avoid reaching these tipping points.

But for Snowball Earth, they couldn't have come soon enough.

What started as a trickle...

..has become a torrent.

As the ice starts to melt, the exposed dark surfaces

suck in ever more warmth from the sun.

The melt becomes unstoppable.

A runaway train that releases a staggering deluge of water.

Sea levels rise two metres every decade,

swallowing great chunks of coastline.

After a total of over 50 million gruelling years in deep freeze...

..the world is finally reborn.

Snowball Earth was an unprecedented assault on our planet.

An astonishing moment that left no corner of the world unscathed.

You and I are here because, through it all, life survived.

But as tenacious as it was, that life was still single-celled

and still trapped in the microscopic world.

But this is more than just a tale of simple survival.

In the shattered remains of the great freeze, the stage was

set for a revolution that would change beyond all recognition.

It's easy to assume that life progresses in a straight line,

steadily becoming more complex, more advanced.

But in reality, it's often not like that. Often it relies upon a great

shock to the system, a state change, to flip life onto another path.

After which, that life and the world in which it lives,

are never the same again.

Snowball Earth was just such a moment.

The ice of the great freeze

had shredded the surface of our planet...

..ripping up millions upon millions of tons of rock

and dumping it into the oceans.

This sudden flood of resources causes single-celled algae

and bacteria to flourish throughout the waters of the world.

Their vivid blooms so large they're visible from space...

..stretching across entire oceans.

Growth on such a staggering scale has the power to change

the entire ecosystem.

All this photosynthesising greatly increases

levels of oxygen in the water,

an element vital for complex life.

When the algae and bacteria eventually die, billions upon

billions drift down to the bottom,

a rain of organic matter...

..adding to millions of years worth of dead things that have built

up over the history of the oceans.

And bacteria living at the bottom of the ocean gorged

themselves on this dead matter...

..reprocessing it and releasing a steady stream of minerals

back into the water column...

..giving our ancient ancestors a plentiful, sustained source

of food, oxygen and nutrients,

all supplied by life itself.

At this moment, for the first time ever, life and the planet

come together to become complimentary cogs spinning in

a great nutrient recycling machine, which is providing life with

exactly what it wants in quantities that it's never had before.

And as a consequence, life explodes.

And after around half a billion years of struggle,

Earth's fledgling spring is set to become a glorious summer.

In shallow coastal waters across the planet, life blossoms.

These may look like plants, but they are the first animals.

Leaf-shaped Charnia feed on passing nutrients...

..whilst Attenborites float freely on the tides.

They're the descendants of those first tiny eukaryote pioneers,

now evolved into myriad strange forms,

all of which have finally broken free of the microscopic world.

These are creatures of a complexity and size that we could see,

could reach out and touch.

All living with, and supported by, an ecosystem

just as intricate and remarkable as any on Earth today.

These first truly complex living creatures

are now long gone.

But they were the first to take this great leap,

and once they had, for life, there was no looking back.

All thanks to Snowball Earth lighting the fuse.

Snowball Earth was an astonishing period,

when life, land and the climate were in conflict like never before.

When that long winter ended,

the stage was set for evolution to run riot.

And finally, it's created all of the fantastic scale, the

remarkable diversity and the amazing beauty of life on Earth today.

How do scientists study the bizarre animal life of the Ediacaran,

which lived more than 500 million years ago?

- So, this is a wonderful fossil from Charnwood Forest in Leicestershire

in the UK, and it was found by schoolchildren in the '50s.

While it looks superficially like a plant,

because it lived in very deep water, we know it can't have lived

off the light, been photosynthetic. Instead, it fed from the little

bacteria and the dissolved organic carbon that were floating past it.

- These creatures are so unusual,

understanding how they interact with each other can be difficult.

Now, thanks to advanced laser technology,

scientists can learn more about them than ever before.

- So, by laser scanning these fossils, we've got

a three-dimensional surface, and what this means is, you have

essentially a snap-shot of Ediacaran life captured on the rock surfaces.

To date, we have over 20,000 fossils that we've laser scanned,

and using different sorts of statistics

and mathematical approaches, we can then work out what

they were doing and how they were interacting with each other.

- And analysing spatial patterns within the scans has revealed

why some of these creatures grew so big.

- For a long time, we thought that the reason they got large

and grew things like stems was to get food without having to compete,

and what we found is that, actually, competition's very, very rare.

Being big wasn't an advantage for getting food,

but what it was an advantage for was ensuring

that your offspring got to go as far as possible, because the taller

you are, the further your offspring will travel in the water column.

- And the scans have also led to the discovery that some organisms

had unexpected behaviours.

- We actually found something rather surprising. They don't always

reproduce sexually. Instead, some of them reproduce little clones

of themselves that are attached by filaments or runners, a bit like

strawberry plants or spider plants, and so the fossils you see are

actually clones of their parents, and even grandparents sometimes.

- After Snowball Earth, the evolution of complex life

occurred at a rate never seen before.

- We've gone from these tiny, microscopic, little fossils,

that we can only see with microscopes, all the way to these

large, complex organisms which show signs of having animal features.

- There's always a possibility that without Snowball Earth,

life wouldn't have evolved into the complex,

large organisms that we see around us today.

- Next time...

The story of how the Earth turned green,

as plants rose from the oceans...

..to conquer a hostile land...

..but whose domination almost wiped out all life on the planet.

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

Well, the Open University imagined 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.