Original subtitles

For 90% of our planet's history,

it has been too warm for ice to form.

So when the Ice Age hit two and a half million years ago,

its impact was huge.

This is the story of a great freeze

and the rise of a dynasty

that would bring life to the brink of extinction.

Yellowstone is one of the coldest places in America.

In winter, it still endures some of the same freezing conditions

that an ice age brings.

Temperatures can drop below minus 50 degrees.

Only those built for the cold can survive.

A bison's thick coat is such good insulation,

they need little energy to keep warm...

which is just as well,

as grass is hard to find beneath the snow.

But bison aren't the only hungry ones here.

Wolves can also withstand the coldest of winters...

and have been hunting bison in America for more than 100,000 years.

To split up the herd...

...the pack needs to get them moving.

Panic gives the wolves control.

The herd must stick together.

One trip could prove fatal.

But the bison can't run forever,

especially in the deep snow.

Their only hope is to turn and face their pursuers.

Only then does the pack finally relent.

But no matter where they go,

the wolves will follow.

Age-old enemies that have been locked in battle for millennia.

Yet these ancient adversaries are lucky...

for they can look forward to the end of winter

and the relief of spring.

But there was a time when winter

never seemed to end.

Two and a half million years ago,

changes in the Earth's orbit,

ocean currents, and carbon dioxide levels

led to an abrupt cooling of the planet.

The great Ice Age had begun...

...and it started with the tiniest of things.

On its own, a snowflake is a fragile, frozen wonder.

No two the same.

But together, snowflakes changed the world.

Without warm summers to melt them,

snow blanketed the north of the globe...

...and, over thousands of years, compacted

to form permanent ice sheets several kilometers thick.

Here, in this silent realm,

life was frozen out of existence.

But south of the ice sheets,

a new world was created where life could thrive.

Circling almost the entire Northern Hemisphere,

the tundra-steppe became Earth's most extensive habitat.

Mammals that adapted well to the cold dominated these frigid lands...

including the largest and most iconic of them all...

...woolly mammoths.

Their elephant-like ancestors

left Africa millions of years earlier

and evolved into these highly specialized beasts.

Long hair, smaller ears, and shorter tails

help them conserve heat in the cold.

They are guided by an old female, the matriarch,

who passes her knowledge down the generations.

Generations she needs to keep safe.

Bigger than lions today,

cave lions can bring down the very largest of prey.

But smaller is easier.

With little cover, the brazen cats don't even try to hide.

Instead, they bide their time,

waiting for the right moment.

The calf must stay close to its protectors...

but the hunters have him in their sights.

The mammoths form a wall of tusks...

...but the lions aren't going anywhere.

The matriarch has had enough...

...but one of the hunters spots an opportunity.

The teenager will never stray from the herd again.

Now it's the lions' turn to defend.

The calf's mother...

...knows it's a lost cause.

They have no choice but to back down

and protect the generations that remain.

All they can do is continue their migration

across the cold tundra-steppe.

While ice never completely engulfed the planet,

its impact was still felt across the globe...

sometimes in the most unexpected ways.

With most of the world's water locked up as ice,

the land became increasingly dry.

This is the flip side of an ice age.

South of the tundra-steppe,

the deserts almost doubled in size,

devouring everything in their path.

Only desert specialists that had evolved to withstand extreme heat

could survive such hostile conditions.

But the drying didn't stop there.

Even further south, Africa's tropical rainforests,

stable sanctuaries for life for over 50 million years,

almost completely disappeared...

...replaced by a vast expanse of dry forest and grassland.

The impact on life was huge,

not least on one group of animals...

...the primates.

Baboons share 94% of their DNA with us,

as well as a crucial part of our story.

The descent from the treetops to a life on the forest floor.

Down here, during the Ice Age,

our cousins faced many new challenges.

Life on the ground is more dangerous...

...home to large predators.

Fortunately, what primates lack in strength and size,

we make up for with intelligence and large families.

But finding enough food to feed many mouths...

...is a constant challenge.

So when food is found,

it attracts plenty of attention.

And where there's a precious resource...

...conflict is inevitable...

...not least with your own kind.

A rival troop with no appetite for sharing.

In the dry forest,

every fruit is worth fighting for...

...and every fight counts.

The rival troop cut their losses.

But they'll be back.

To overcome the challenges of a more hostile world,

primates relied on their social intelligence,

a trait that, in time,

would lead to one species of primate achieving global domination.

The buildup of ice in the north affected the climate across the planet.

But just as life got used to colder, drier conditions,

everything changed.

The ice began to melt as Earth's orbit shifted once more

and global temperatures began to rise.

What started as a series of meltwater streams

soon turned into a deluge.

In North America, the meltwater formed an enormous glacial lake

600 meters deep and covering 10,000 square kilometers.

The only thing stopping the water from flooding the land to the west

was a towering wall of ice.

On the far side, the wall was almost a kilometer high...

...a seemingly unstoppable barrier...

but not for much longer.

As temperatures kept rising and the meltwater lake kept growing,

the pressure from behind increased.

Before long, the walls started to crumble from the inside out...

until finally, catastrophic collapse.

In an instant, a lake the size of the Irish Sea is unleashed.

Thirty kilometers south,

and the first hint of the coming apocalypse.

Tremors.

They sense danger...

...but there's nowhere to hide.

The first they see is a wall of dust.

A hundred meters high,

it's the vanguard of a giant tsunami.

In just ten hours,

the megaflood smashes an 800-kilometer-long path

through the American continent, all the way to the ocean.

Natural wonders that might otherwise take millennia to form

are created in a matter of hours.

But these spectacles are short-lived.

Just a few days later,

all that remains

is an eerie silence.

The indelible scars of this megaflood still mark the American landscape today...

yet since the dawn of the Ice Age,

there have been more than 50 cycles of ice buildup and melt...

each causing its own epic floods.

Once the turmoil of the last great melt subsided,

balance slowly returned across the land.

Rainfall became more regular...

allowing forests to bounce back.

Deserts shrunk and greened

as, once again, water flowed.

And where water flows,

life soon follows.

Europe's Danube delta

is one of the largest wetlands in the world.

It formed after the last great melt

and quickly became home to an incredible wealth of animal life.

With so much food on offer,

whiskered terns travel thousands of kilometers

to breed in these rich waters.

It's the perfect place to raise a family...

...but it's a wasted journey

if a male arrives too late to find a female.

All he can do is watch the success of others.

With his rival gone...

...now is his chance.

Food makes an excellent gift...

...but she's not impressed.

He tries his luck nonetheless...

but to no avail.

The spurned male must dine alone.

Only when life is so bountiful can females afford to be so choosy.

The end of the Ice Age ushered in not only a time of plenty...

but also a time of great climate stability...

a time known as the Holocene.

During this period, warm, wet conditions prevailed...

...and average global temperatures

fluctuated by less than one degree Celsius,

allowing life to flourish in every corner of the world...

...each species boasting an unbroken line of ancestry

stretching back four billion years

to the very origin of life on Earth.

However, not everything thrived during the Holocene.

A strange and highly selective extinction was underway.

Across the planet,

the largest land animals were disappearing.

Mammoths, cave lions, and hundreds of other species vanished.

North America was particularly hard-hit,

losing over 70% of its giants...

but not all.

In the absence of competitors,

bison took over the great plains...

...roaming in huge numbers.

But they weren't alone.

With fewer big prey to choose from,

bison became the focus of another group of survivors.

Age-old enemies.

Their best defense is to keep an eye on the danger,

stick together, and calmly move on.

But these are no ordinary hunters...

...for the Ice Age saw the spread of a new predator.

Like wolves,

we hunted in groups.

And what we lacked in strength and speed...

we made up for with intelligence and cunning.

The evolution of our large, complex brains

had set us apart from other primates

and enabled us to hunt in increasingly sophisticated ways.

Mimicking wolves

and using carefully placed stone stacks,

hunters corralled the bison for miles,

until they were exactly

where they wanted them.

Only then do they close in behind the herd.

Reveal themselves too soon

and days of effort will be wasted.

Their ultimate prize isn't the death of one,

but the fall of many...

to feed many over the winter months.

The trap is set.

All they need is a little encouragement.

By the early Holocene,

humans had spread out of Africa to almost every continent on Earth

and become the world's most dangerous predator.

While our rise contributed

to the global extinction of large land animals,

our story could have been a short one

had we not done something remarkable.

We freed ourselves from the uncertainty of a hunter-gatherer existence

by forming alliances with nature.

The stable climate of the Holocene

enabled our ancestors to develop a unique relationship

with plants.

They hand-selected certain species

and sowed their seeds where they were best able to grow.

All this care and attention

dramatically increased the plants' chances of survival,

and in return, humans could reap the rewards.

They learned how to produce more food

and to make it last all year round.

And where their plants grew,

people prospered.

Our ancestors discovered how to ensure a stable food supply.

And it wasn't just plants they domesticated.

Animals too.

Across the world,

many hunter-gatherers gave up their nomadic lifestyles

in favor of farming.

Slowly but surely, the wilderness was transformed,

tamed by human hands.

Freed from the constant battle to find food,

human populations grew,

work diversified,

society became more complex...

and civilizations were born.

We achieved something no other species has ever done.

We broke free of nature and rose above it.

Agriculture changed everything...

but another revolution was coming.

Our ingenuity has taken us further than we could ever have imagined,

and our story is now written on the surface of the Earth.

What was once wild has been tamed or lost.

We're too successful for our own good

and for that of the planet...

and we are now causing the next mass extinction.

It's not just that simply feeding ourselves

takes up more than half of all habitable land...

and it's not just that the carbon dioxide we are releasing

is heating our planet faster

than at any time in the last 500 million years.

Nor is it just that we are warming and acidifying the oceans,

destroying their natural balance

and killing off vast swathes of marine life.

Nor is it just that we are causing extreme weather events...

...fire and drought

that are returning the Earth to its barren beginnings.

And it's not just that we are doing any one of these

but that we are doing all of them,

all at the same time.

And to make matters worse,

we are doing it at meteoric speed.

Although rare, mass extinctions change the course of history like nothing else.

So far, Earth has endured five of these apocalyptic events,

each one wiping out more than three-quarters of all life.

What's more, the dominant species going in

are not the dominant species coming out.

The impact of a mass extinction

has not been felt for 66 million years.

Now we're on track

for the sixth.

In the last 50 years alone,

wildlife populations have fallen by an average of almost 70%,

and this time, we are the ones responsible.

And yet despite this grim forecast,

there remains a glimmer of hope.

We are the first species in the four-billion-year story of life

to understand what is happening to our world.

We are also the first species

to understand what is needed to put it right.

Our intelligence has brought us this far,

and it's the only thing that can save us.

Our future, and that of the planet,

is yet to be written.

How we act now will determine the next chapter...

...in the story of life.

But whatever future awaits...

...if there's one thing we've learned from the past...

it's that life has always found a way.