[wind howling]
[Morgan Freeman] 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.
[poignant music playing]
[grunting]
This is the story of a great freeze
and the rise of a dynasty
that would bring life to the brink of extinction.
[music intensifies]
-[music ends] -[echoing howls]
[rousing music playing]
[snarling]
[trilling]
[screeching]
[rousing music continues]
[growling]
[wind howling]
[rumbling]
[rousing music intensifies]
[music fades]
[ambient music playing]
[bird caws]
[ethereal vocalizing]
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.
[grunting]
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.
[snorts]
But bison aren't the only hungry ones here.
[high-pitched squawking]
[howling]
Wolves can also withstand the coldest of winters…
and have been hunting bison in America for more than 100,000 years.
[grunting]
To split up the herd…
[snorts]
…the pack needs to get them moving.
[bison grunting]
Panic gives the wolves control.
[tense music playing]
The herd must stick together.
One trip could prove fatal.
But the bison can't run forever,
especially in the deep snow.
[grunting]
[wolves whining, growling]
[wolf growls]
[grunting]
Their only hope is to turn and face their pursuers.
[panting]
[grunting]
Only then does the pack finally relent.
[bison grunting]
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.
[bison bellowing]
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…
[ethereal music playing]
…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…
[music ends]
…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…
[creatures rumbling]
…woolly mammoths.
Their elephant-like ancestors
left Africa millions of years earlier
and evolved into these highly specialized beasts.
[rumbling]
Long hair, smaller ears, and shorter tails
help them conserve heat in the cold.
[roaring]
They are guided by an old female, the matriarch,
who passes her knowledge down the generations.
[roars]
Generations she needs to keep safe.
[roaring, snorting]
[ominous music playing]
[growling]
[snarling]
Bigger than lions today,
cave lions can bring down the very largest of prey.
[mewling]
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.
[grunting]
[trumpeting]
[roaring]
-[snarling] -[mammoths trumpeting]
The mammoths form a wall of tusks…
[snarling]
…but the lions aren't going anywhere.
[snarling]
[roaring]
[trumpeting]
[snarling]
The matriarch has had enough…
-[snarling] -[trumpeting]
…but one of the hunters spots an opportunity.
[tense music playing]
[snarling]
-[growls] -[bellowing]
The teenager will never stray from the herd again.
[snarling]
[growling]
[roaring]
[snarling]
Now it's the lions' turn to defend.
-[roaring] -[snarling]
The calf's mother…
[roaring]
…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.
[unsettling music playing]
[whispered vocalizing]
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…
[stirring music playing]
[music ends abruptly]
…replaced by a vast expanse of dry forest and grassland.
The impact on life was huge,
not least on one group of animals…
[honks, yaps]
…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…
[tense music playing]
[baboon barking]
…home to large predators.
Fortunately, what primates lack in strength and size,
we make up for with intelligence and large families.
[gentle music playing]
But finding enough food to feed many mouths…
[chirping]
…is a constant challenge.
[elephant growling]
So when food is found,
it attracts plenty of attention.
[grunting]
-And where there's a precious resource… -[elephant snorts]
[screeching]
…conflict is inevitable…
-[warthog squeals] -[baboon grunts]
…not least with your own kind.
[tense, dramatic music playing]
A rival troop with no appetite for sharing.
[barks]
[clicking]
[grunting]
-[barking] -[screeching]
In the dry forest,
every fruit is worth fighting for…
[screeching]
[barking]
…and every fight counts.
[energetic music playing]
[screeching]
[music slows]
[screeching]
The rival troop cut their losses.
-[clicking] -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.
[ominous music playing]
[music ends]
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.
[somber music playing]
What started as a series of meltwater streams
soon turned into a deluge.
[somber music continues]
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…
[ominous music playing]
…a seemingly unstoppable barrier…
but not for much longer.
[faint rumbling]
As temperatures kept rising and the meltwater lake kept growing,
the pressure from behind increased.
[creaking, rumbling]
Before long, the walls started to crumble from the inside out…
until finally, catastrophic collapse.
[dramatic music playing]
In an instant, a lake the size of the Irish Sea is unleashed.
[music fades]
[birds tweeting]
Thirty kilometers south,
and the first hint of the coming apocalypse.
[faint rumbling]
Tremors.
[chirping]
They sense danger…
[whinnying]
…but there's nowhere to hide.
[rumbling intensifies]
[whinnying]
The first they see is a wall of dust.
A hundred meters high,
it's the vanguard of a giant tsunami.
[epic music playing]
[music fades]
In just ten hours,
the megaflood smashes an 800-kilometer-long path
through the American continent, all the way to the ocean.
[mournful music playing]
Natural wonders that might otherwise take millennia to form
are created in a matter of hours.
[ethereal music playing]
But these spectacles are short-lived.
Just a few days later,
all that remains
is an eerie silence.
[music fades to 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.
[optimistic music playing]
Once the turmoil of the last great melt subsided,
balance slowly returned across the land.
Rainfall became more regular…
allowing forests to bounce back.
[chirping, tweeting]
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…
[chirping]
…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.
[chirping]
[slow, playful music playing]
With his rival gone…
[chirping]
…now is his chance.
[chirping]
Food makes an excellent gift…
[chirping]
…but she's not impressed.
[chirping]
He tries his luck nonetheless…
but to no avail.
[chirps]
The spurned male must dine alone.
Only when life is so bountiful can females afford to be so choosy.
[chirping]
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…
[trumpeting]
…and average global temperatures
fluctuated by less than one degree Celsius,
allowing life to flourish in every corner of the world…
[squawking]
…each species boasting an unbroken line of ancestry
stretching back four billion years
to the very origin of life on Earth.
[gentle music playing]
[trilling]
[music fades]
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…
-[grunting] -…roaming in huge numbers.
-[grunting] -But they weren't alone.
[ominous music playing]
With fewer big prey to choose from,
bison became the focus of another group of survivors.
[grunting]
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…
[grunting]
…for the Ice Age saw the spread of a new predator.
[ominous music continues]
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.
[slow, majestic music playing]
Mimicking wolves
and using carefully placed stone stacks,
hunters corralled the bison for miles,
until they were exactly
where they wanted them.
[music fades]
[bison grunting]
Only then do they close in behind the herd.
[grunting]
Reveal themselves too soon
and days of effort will be wasted.
[ominous music playing]
Their ultimate prize isn't the death of one,
but the fall of many…
to feed many over the winter months.
[grunting]
The trap is set.
All they need is a little encouragement.
[hunters shrieking]
-[shrieking] -[dramatic music playing]
[grunting]
[music ends]
[grunting]
[dramatic music resumes]
[music ends]
[rocks clattering]
[dull thud]
By the early Holocene,
humans had spread out of Africa to almost every continent on Earth
and become the world's most dangerous predator.
[distant cries]
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.
[suspenseful music playing]
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.
[gentle music playing]
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.
[cattle lowing]
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.
[rousing music playing]
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.
[rousing music intensifies]
[music fades]
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.
[solemn music playing]
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…
[thunder crashing]
…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.
[music quickens]
[music ends abruptly]
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.
[gentle, optimistic music playing]
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.
[ethereal vocalizing]
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…
[baby gurgling]
…in the story of life.
-[echoing crash] -[water dripping]
-[music fades] -[thunder rumbling]
But whatever future awaits…
[ominous music playing]
…if there's one thing we've learned from the past…
it's that life has always found a way.
[eerie music playing]
[birds tweeting]
[tweeting growing louder]
[eerie music intensifies]
[music fades]
[rousing music playing]