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For 90%
of our planet's history,
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it has been too warm for ice to form.
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00:00:23,732 --> 00:00:28,445
So when the Ice Age hit
two and a half million years ago,
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00:00:29,279 --> 00:00:31,740
its impact was huge.
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This is the story of a great freeze
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and the rise of a dynasty
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that would bring life
to the brink of extinction.
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Yellowstone is one of the coldest places
in America.
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In winter, it still endures
some of the same freezing conditions
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that an ice age brings.
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Temperatures can drop
below minus 50 degrees.
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Only those built for the cold can survive.
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A bison's thick coat
is such good insulation,
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they need little energy to keep warm...
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which is just as well,
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as grass is hard to find beneath the snow.
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But bison aren't
the only hungry ones here.
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Wolves can also withstand
the coldest of winters...
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and have been hunting bison in America
for more than 100,000 years.
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To split up the herd...
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...the pack needs to get them moving.
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Panic gives the wolves control.
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The herd must stick together.
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One trip could prove fatal.
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But the bison can't run forever,
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especially in the deep snow.
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Their only hope
is to turn and face their pursuers.
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Only then does the pack finally relent.
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But no matter where they go,
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the wolves will follow.
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Age-old enemies that have been
locked in battle for millennia.
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Yet these ancient adversaries are lucky...
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for they can look forward
to the end of winter
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and the relief of spring.
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But there was a time when winter
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{\an8}never seemed to end.
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{\an8}Two and a half million years ago,
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changes in the Earth's orbit,
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ocean currents, and carbon dioxide levels
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led to an abrupt cooling of the planet.
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The great Ice Age had begun...
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...and it started
with the tiniest of things.
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00:07:15,351 --> 00:07:21,983
On its own, a snowflake
is a fragile, frozen wonder.
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No two the same.
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But together,
snowflakes changed the world.
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Without warm summers to melt them,
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snow blanketed the north of the globe...
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...and, over thousands of years, compacted
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to form permanent ice sheets
several kilometers thick.
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Here, in this silent realm,
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life was frozen out of existence.
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But south of the ice sheets,
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a new world was created
where life could thrive.
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Circling almost
the entire Northern Hemisphere,
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{\an8}the tundra-steppe
became Earth's most extensive habitat.
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Mammals that adapted well to the cold
dominated these frigid lands...
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including the largest
and most iconic of them all...
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...woolly mammoths.
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Their elephant-like ancestors
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left Africa millions of years earlier
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and evolved
into these highly specialized beasts.
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Long hair, smaller ears, and shorter tails
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help them conserve heat in the cold.
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They are guided by an old female,
the matriarch,
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who passes her knowledge
down the generations.
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Generations she needs to keep safe.
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Bigger than lions today,
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cave lions can bring down
the very largest of prey.
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But smaller is easier.
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With little cover,
the brazen cats don't even try to hide.
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Instead, they bide their time,
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waiting for the right moment.
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The calf must stay close
to its protectors...
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but the hunters have him in their sights.
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The mammoths form a wall of tusks...
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...but the lions aren't going anywhere.
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The matriarch has had enough...
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...but one of the hunters
spots an opportunity.
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The teenager will never stray
from the herd again.
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Now it's the lions' turn to defend.
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The calf's mother...
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...knows it's a lost cause.
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They have no choice but to back down
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and protect the generations that remain.
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All they can do
is continue their migration
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across the cold tundra-steppe.
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While ice never completely
engulfed the planet,
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its impact was still felt
across the globe...
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sometimes in the most unexpected ways.
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With most of the world's water
locked up as ice,
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the land became increasingly dry.
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This is the flip side of an ice age.
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South of the tundra-steppe,
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the deserts almost doubled in size,
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devouring everything in their path.
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Only desert specialists that had evolved
to withstand extreme heat
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could survive such hostile conditions.
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But the drying didn't stop there.
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Even further south,
Africa's tropical rainforests,
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stable sanctuaries for life
for over 50 million years,
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almost completely disappeared...
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...replaced by a vast expanse
of dry forest and grassland.
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The impact on life was huge,
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not least on one group of animals...
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...the primates.
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Baboons share 94% of their DNA with us,
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as well as a crucial part of our story.
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The descent from the treetops
to a life on the forest floor.
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Down here, during the Ice Age,
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our cousins faced many new challenges.
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Life on the ground is more dangerous...
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...home to large predators.
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Fortunately, what primates lack
in strength and size,
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we make up for
with intelligence and large families.
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But finding enough food
to feed many mouths...
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...is a constant challenge.
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So when food is found,
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it attracts plenty of attention.
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And where there's a precious resource...
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...conflict is inevitable...
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...not least with your own kind.
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A rival troop
with no appetite for sharing.
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In the dry forest,
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every fruit is worth fighting for...
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...and every fight counts.
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The rival troop cut their losses.
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But they'll be back.
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To overcome the challenges
of a more hostile world,
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primates relied
on their social intelligence,
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a trait that, in time,
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would lead to one species of primate
achieving global domination.
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The buildup of ice in the north
affected the climate across the planet.
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But just as life got used
to colder, drier conditions,
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everything changed.
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The ice began to melt
as Earth's orbit shifted once more
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and global temperatures began to rise.
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What started as a series
of meltwater streams
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soon turned into a deluge.
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In North America, the meltwater
formed an enormous glacial lake
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600 meters deep
and covering 10,000 square kilometers.
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The only thing stopping the water
from flooding the land to the west
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was a towering wall of ice.
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On the far side,
the wall was almost a kilometer high...
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...a seemingly unstoppable barrier...
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but not for much longer.
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As temperatures kept rising
and the meltwater lake kept growing,
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the pressure from behind increased.
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Before long, the walls started to crumble
from the inside out...
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until finally, catastrophic collapse.
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In an instant, a lake the size
of the Irish Sea is unleashed.
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Thirty kilometers south,
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and the first hint
of the coming apocalypse.
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Tremors.
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They sense danger...
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...but there's nowhere to hide.
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The first they see is a wall of dust.
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A hundred meters high,
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it's the vanguard of a giant tsunami.
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In just ten hours,
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the megaflood smashes
an 800-kilometer-long path
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through the American continent,
all the way to the ocean.
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Natural wonders that might otherwise
take millennia to form
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are created in a matter of hours.
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But these spectacles are short-lived.
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Just a few days later,
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all that remains
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is an eerie silence.
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The indelible scars of this megaflood
still mark the American landscape today...
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yet since the dawn of the Ice Age,
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there have been more than 50 cycles
of ice buildup and melt...
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each causing its own epic floods.
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Once the turmoil
of the last great melt subsided,
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balance slowly returned across the land.
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Rainfall became more regular...
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allowing forests to bounce back.
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Deserts shrunk and greened
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as, once again, water flowed.
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And where water flows,
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life soon follows.
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Europe's Danube delta
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is one of the largest wetlands
in the world.
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It formed after the last great melt
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and quickly became home
to an incredible wealth of animal life.
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With so much food on offer,
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whiskered terns travel
thousands of kilometers
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to breed in these rich waters.
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It's the perfect place to raise a family...
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...but it's a wasted journey
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if a male arrives too late
to find a female.
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All he can do
is watch the success of others.
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With his rival gone...
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...now is his chance.
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Food makes an excellent gift...
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...but she's not impressed.
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He tries his luck nonetheless...
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but to no avail.
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The spurned male must dine alone.
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Only when life is so bountiful
can females afford to be so choosy.
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The end of the Ice Age
ushered in not only a time of plenty...
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but also a time
of great climate stability...
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a time known as the Holocene.
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During this period,
warm, wet conditions prevailed...
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...and average global temperatures
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00:30:51,516 --> 00:30:55,228
fluctuated by
less than one degree Celsius,
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00:30:56,771 --> 00:31:01,818
allowing life to flourish
in every corner of the world...
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00:31:08,616 --> 00:31:13,663
...each species boasting
an unbroken line of ancestry
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stretching back four billion years
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00:31:16,916 --> 00:31:19,794
to the very origin of life on Earth.
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00:31:45,278 --> 00:31:50,158
However, not everything thrived
during the Holocene.
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A strange and highly selective extinction
was underway.
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Across the planet,
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00:32:03,004 --> 00:32:06,174
the largest land animals
were disappearing.
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00:32:07,342 --> 00:32:12,805
Mammoths, cave lions,
and hundreds of other species vanished.
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00:32:15,683 --> 00:32:18,186
North America was particularly hard-hit,
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losing over 70% of its giants...
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00:32:25,777 --> 00:32:27,278
but not all.
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00:32:29,697 --> 00:32:32,033
In the absence of competitors,
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00:32:32,951 --> 00:32:36,079
bison took over the great plains...
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00:32:36,162 --> 00:32:39,624
...roaming in huge numbers.
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00:32:55,306 --> 00:32:57,392
But they weren't alone.
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With fewer big prey to choose from,
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00:33:08,987 --> 00:33:12,490
bison became the focus
of another group of survivors.
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Age-old enemies.
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00:33:27,380 --> 00:33:31,426
Their best defense
is to keep an eye on the danger,
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00:33:33,094 --> 00:33:36,431
stick together, and calmly move on.
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00:33:40,935 --> 00:33:43,229
But these are no ordinary hunters...
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...for the Ice Age saw the spread
of a new predator.
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00:34:01,581 --> 00:34:02,707
Like wolves,
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00:34:03,499 --> 00:34:05,334
we hunted in groups.
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00:34:08,880 --> 00:34:11,299
And what we lacked in strength and speed...
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00:34:13,634 --> 00:34:18,264
we made up for
with intelligence and cunning.
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00:34:21,225 --> 00:34:25,188
The evolution of our large, complex brains
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00:34:25,271 --> 00:34:28,066
had set us apart from other primates
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00:34:29,484 --> 00:34:33,780
and enabled us to hunt
in increasingly sophisticated ways.
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Mimicking wolves
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and using carefully placed stone stacks,
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00:34:46,751 --> 00:34:50,797
hunters corralled the bison for miles,
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until they were exactly
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where they wanted them.
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Only then do they close in
behind the herd.
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Reveal themselves too soon
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and days of effort will be wasted.
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00:35:38,177 --> 00:35:41,013
Their ultimate prize
isn't the death of one,
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but the fall of many...
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00:35:49,689 --> 00:35:53,067
to feed many over the winter months.
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00:36:02,326 --> 00:36:04,453
The trap is set.
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00:36:09,876 --> 00:36:14,005
All they need is a little encouragement.
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00:37:00,468 --> 00:37:02,345
By the early Holocene,
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00:37:02,970 --> 00:37:08,142
humans had spread out of Africa
to almost every continent on Earth
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00:37:09,185 --> 00:37:13,022
and become
the world's most dangerous predator.
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While our rise contributed
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00:37:19,820 --> 00:37:22,949
to the global extinction
of large land animals,
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00:37:23,824 --> 00:37:26,869
our story could have been a short one
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00:37:28,621 --> 00:37:31,207
had we not done something remarkable.
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00:37:34,961 --> 00:37:40,299
We freed ourselves from the uncertainty
of a hunter-gatherer existence
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00:37:41,008 --> 00:37:44,262
by forming alliances with nature.
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00:37:47,223 --> 00:37:49,600
The stable climate of the Holocene
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00:37:49,684 --> 00:37:53,604
enabled our ancestors
to develop a unique relationship
259
00:37:55,856 --> 00:37:57,066
with plants.
260
00:38:02,280 --> 00:38:04,699
They hand-selected certain species
261
00:38:05,449 --> 00:38:09,745
and sowed their seeds
where they were best able to grow.
262
00:38:16,294 --> 00:38:18,587
All this care and attention
263
00:38:18,671 --> 00:38:22,717
dramatically increased
the plants' chances of survival,
264
00:38:24,176 --> 00:38:29,098
and in return,
humans could reap the rewards.
265
00:38:33,978 --> 00:38:36,480
They learned how to produce more food
266
00:38:37,064 --> 00:38:40,234
and to make it last all year round.
267
00:38:44,363 --> 00:38:46,073
And where their plants grew,
268
00:38:47,992 --> 00:38:49,452
people prospered.
269
00:38:53,080 --> 00:38:58,544
Our ancestors discovered
how to ensure a stable food supply.
270
00:39:00,546 --> 00:39:03,966
And it wasn't just plants
they domesticated.
271
00:39:05,468 --> 00:39:06,802
Animals too.
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00:39:08,512 --> 00:39:09,930
Across the world,
273
00:39:10,014 --> 00:39:14,769
many hunter-gatherers
gave up their nomadic lifestyles
274
00:39:17,021 --> 00:39:19,231
in favor of farming.
275
00:39:20,524 --> 00:39:25,946
Slowly but surely,
the wilderness was transformed,
276
00:39:27,198 --> 00:39:29,950
tamed by human hands.
277
00:39:32,370 --> 00:39:35,414
Freed from the constant battle
to find food,
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00:39:36,207 --> 00:39:38,209
human populations grew,
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00:39:39,794 --> 00:39:41,796
work diversified,
280
00:39:43,422 --> 00:39:46,092
society became more complex...
281
00:39:49,095 --> 00:39:52,014
and civilizations were born.
282
00:39:58,979 --> 00:40:04,026
We achieved something
no other species has ever done.
283
00:40:05,152 --> 00:40:10,032
We broke free of nature and rose above it.
284
00:40:11,575 --> 00:40:15,371
Agriculture changed everything...
285
00:40:17,748 --> 00:40:21,335
but another revolution was coming.
286
00:41:13,762 --> 00:41:19,894
Our ingenuity has taken us further
than we could ever have imagined,
287
00:41:21,854 --> 00:41:26,942
and our story is now written
on the surface of the Earth.
288
00:41:30,488 --> 00:41:36,327
What was once wild has been tamed or lost.
289
00:41:40,831 --> 00:41:43,792
We're too successful for our own good
290
00:41:45,044 --> 00:41:46,921
and for that of the planet...
291
00:41:49,465 --> 00:41:54,303
and we are now causing
the next mass extinction.
292
00:42:00,142 --> 00:42:03,812
It's not just
that simply feeding ourselves
293
00:42:03,896 --> 00:42:06,982
takes up more than half
of all habitable land...
294
00:42:21,830 --> 00:42:26,168
and it's not just
that the carbon dioxide we are releasing
295
00:42:26,252 --> 00:42:28,337
is heating our planet faster
296
00:42:28,420 --> 00:42:32,925
than at any time
in the last 500 million years.
297
00:42:40,057 --> 00:42:45,396
Nor is it just that we are warming
and acidifying the oceans,
298
00:42:46,981 --> 00:42:49,483
destroying their natural balance
299
00:42:49,567 --> 00:42:53,571
and killing off
vast swathes of marine life.
300
00:42:57,116 --> 00:43:01,954
Nor is it just that we are causing
extreme weather events...
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00:43:03,497 --> 00:43:04,790
...fire and drought
302
00:43:05,958 --> 00:43:09,920
that are returning the Earth
to its barren beginnings.
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00:43:15,217 --> 00:43:18,679
And it's not just that we are doing
any one of these
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00:43:19,847 --> 00:43:22,683
but that we are doing all of them,
305
00:43:23,475 --> 00:43:28,022
all at the same time.
306
00:43:29,982 --> 00:43:32,484
And to make matters worse,
307
00:43:33,444 --> 00:43:36,322
we are doing it at meteoric speed.
308
00:43:46,707 --> 00:43:53,707
Although rare, mass extinctions change
the course of history like nothing else.
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00:43:55,841 --> 00:44:01,680
So far, Earth has endured
five of these apocalyptic events,
310
00:44:02,931 --> 00:44:07,978
each one wiping out
more than three-quarters of all life.
311
00:44:11,440 --> 00:44:14,693
What's more, the dominant species going in
312
00:44:15,319 --> 00:44:19,573
are not the dominant species coming out.
313
00:44:23,786 --> 00:44:26,580
The impact of a mass extinction
314
00:44:26,664 --> 00:44:30,959
has not been felt for 66 million years.
315
00:44:32,378 --> 00:44:35,172
Now we're on track
316
00:44:36,548 --> 00:44:37,758
for the sixth.
317
00:44:45,516 --> 00:44:47,810
In the last 50 years alone,
318
00:44:48,686 --> 00:44:54,233
wildlife populations have fallen
by an average of almost 70%,
319
00:44:55,734 --> 00:45:01,657
and this time,
we are the ones responsible.
320
00:45:04,868 --> 00:45:08,288
And yet despite this grim forecast,
321
00:45:08,997 --> 00:45:12,584
there remains a glimmer of hope.
322
00:45:16,213 --> 00:45:22,928
We are the first species
in the four-billion-year story of life
323
00:45:23,679 --> 00:45:27,891
to understand
what is happening to our world.
324
00:45:30,018 --> 00:45:32,688
We are also the first species
325
00:45:32,771 --> 00:45:36,525
to understand
what is needed to put it right.
326
00:45:38,694 --> 00:45:43,031
Our intelligence has brought us this far,
327
00:45:44,742 --> 00:45:48,412
and it's the only thing that can save us.
328
00:45:55,002 --> 00:45:59,006
Our future, and that of the planet,
329
00:45:59,089 --> 00:46:00,924
is yet to be written.
330
00:46:02,885 --> 00:46:07,055
How we act now
will determine the next chapter...
331
00:46:08,557 --> 00:46:11,351
...in the story of life.
332
00:46:20,319 --> 00:46:23,030
But whatever future awaits...
333
00:46:30,496 --> 00:46:33,373
...if there's one thing
we've learned from the past...
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00:46:39,713 --> 00:46:45,803
it's that life has always found a way.