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[thunder rumbles]
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[poignant music playing]
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[Morgan Freeman] For billions of years,
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much of our world
was fiercely inhospitable...
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[crackling thunder]
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...ravaged by the elements
and the forces of nature.
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[howling wind]
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But this is the story
of what was happening beneath the waves.
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Here, shielded from the storms,
life had taken hold...
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[rumbling thunder]
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...and was about
to change our planet forever.
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[sinister music playing]
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[sinister music intensifies]
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[music ends]
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{\an8}[rousing music playing]
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{\an8}[low growling]
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[snarling]
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{\an8}[trilling]
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{\an8}[screeching]
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{\an8}[rousing music continues]
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[growling]
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[wind howling]
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{\an8}[rumbling]
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[rousing music intensifies]
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[music fades]
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{\an8}[ominous music playing]
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{\an8}Far back in the depths of time,
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Earth looked nothing
like the world we know today.
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Nearly 90% of its surface was water,
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yet this was no blue planet.
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Instead, vast clouds of methane
had turned the atmosphere yellow.
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[thunder rumbles]
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[explosive blast]
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On land, conditions were even worse.
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[repeated blasts]
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Volcanoes had been erupting
for millions of years.
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[rumbling, creaking]
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Their explosive power,
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one of the few sounds
in this otherwise silent realm.
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[ominous music continues]
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With the world made up of nothing
but toxic air and rivers of molten rock...
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life as we know it was impossible.
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[crackling, hissing]
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[stillness]
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But out in the prehistoric seas,
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something is stirring.
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[intriguing music playing]
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Beneath the surface
hangs a great swathe of plankton.
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Microscopic cells like these
have just evolved something new,
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photosynthesis.
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This means they can harness
the sun's energy to grow,
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a breakthrough so important
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that plankton will one day give rise
to every single plant on Earth.
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[intriguing music continues]
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But that's not all.
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One byproduct of photosynthesis is a gas,
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the missing ingredient
for animal life to exist...
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[rousing music playing]
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...oxygen.
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For nearly two billion years,
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plankton produced so much oxygen
that it transformed our planet.
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[stirring music playing]
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No longer hostile,
Earth became a new world,
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where life could finally run wild.
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[music fades]
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[wind blowing]
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Today, millions of years later,
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it's still possible to get a glimpse
of what that next wave of life was like.
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Because in some parts of our shallow seas...
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life still resembles
that more primitive time.
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[whimsical music playing]
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They may not look like it...
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but these are animals...
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very similar
to the first complex life forms.
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Most are soft-bodied
and rooted to the seafloor.
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All have senses.
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And some can even see their surroundings.
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[majestic music playing]
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Many get their food by filter-feeding,
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picking out plankton,
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sometimes in the most curious of ways.
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[slurps]
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[slurping]
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But not all animals here
are stuck in one place.
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Some can move,
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exploring the seafloor
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like their pioneering relatives
millions of years ago.
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It may seem like these shallows
are a kind of Eden,
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a safe haven for life.
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But this is no paradise.
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[ominous music playing]
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Living off modern-day California...
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this is a rainbow nudibranch.
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And its sluggish nature
hides a sinister side...
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because, like its ancestors,
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it's here to hunt.
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It's adapted to a life of predation.
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And its prey of choice,
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anemones.
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But like the very first predators,
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the nudibranch has room for improvement...
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[tense music playing]
103
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...because here, timing...
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is everything.
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Luckily for the hunter,
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its prey is anchored to the seafloor
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and can't hide forever.
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[sinister music playing]
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The anemone's fate?
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To be eaten from the inside out.
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[chomping]
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The arrival of predation
was a seismic shift in the ancient seas.
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The hunted had to adapt
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or risk extinction.
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And one group adapted
in a way never seen before.
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Despite being single animals,
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they were able to separate
into layers of individuals,
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that then broke free.
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Jellyfish.
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530 million years ago,
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they were the very first animals
to escape the seafloor and swim.
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[graceful music playing]
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[tense music playing]
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But predators were already everywhere.
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[dramatic music playing]
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Armed with venomous harpoons,
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these anemones make quick work
of baby jellyfish.
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[tense music playing]
129
00:11:56,132 --> 00:11:57,675
And they are so abundant
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escape seems impossible.
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[tense music continues]
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Caught.
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00:12:25,035 --> 00:12:26,454
But not for long.
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00:12:33,169 --> 00:12:34,920
[tranquil music playing]
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Free at last.
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00:12:51,771 --> 00:12:53,773
Thanks to their ability to swim,
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jellyfish were the first
to venture out of the shallows
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and into the big blue.
139
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[music swells]
140
00:13:11,582 --> 00:13:13,584
[stirring music playing]
141
00:13:23,344 --> 00:13:26,388
Here, with fish yet to evolve,
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jellyfish were entirely free of predation.
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In time, others would follow.
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00:13:39,860 --> 00:13:42,488
But more than half a billion years ago,
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the open ocean belonged to them.
146
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[music swells]
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[music fades]
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[water laps gently]
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For those still stuck on the seabed,
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escaping predation
required a different approach.
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This curious creature
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is a trilobite.
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And its breakthrough adaptation, armor.
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Trilobites are one of the first
in a brand-new dynasty,
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the arthropods.
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They've evolved an external skeleton,
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a shield-like shell
that protects their soft insides.
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00:15:00,941 --> 00:15:04,278
And in these waters, they need it.
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[sinister music playing]
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This is Anomalocaris.
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A bizarre-looking animal,
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its name translates
as "the abnormal shrimp."
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00:15:25,382 --> 00:15:29,762
And in the tropical shallows
508 million years ago,
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it's the world's first apex predator.
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[tense music playing]
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Despite the trilobite's armor,
it makes sense to keep out of sight.
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00:16:00,334 --> 00:16:04,129
But away from the canyons,
there's nowhere to hide...
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00:16:06,507 --> 00:16:09,093
because what makes this hunter so special...
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...is its speed.
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[dramatic music playing]
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Unlike jellyfish, Anomalocaris can swim
with both direction and pace.
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But that isn't always enough...
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because when cornered,
the trilobite's armor comes into its own.
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Rolling into a ball,
it becomes completely impenetrable.
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Even for the abnormal shrimp.
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With the coast clear, the trilobite
continues on its merry way once more.
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It's searching for one
of the ancient ocean's greatest sights...
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[stirring music playing]
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...the trilobite mating grounds,
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where thousands come together to breed.
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In the story of life,
armor has been such a success
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that today, nearly 80% of all animals,
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including insects, spiders, and crabs,
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are related to this ancient arthropod.
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But armor couldn't protect them
from everything.
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{\an8}[ominous music playing]
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Forty million years later,
and a new era of life has begun,
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with more diversity than ever before.
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Here, trilobites are still in their prime,
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but their armor is even more robust...
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00:18:42,830 --> 00:18:48,418
because on this reef,
danger comes from a new type of predator.
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Ancestors of today's octopus and squid,
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these tentacled giants are part
of a dynasty known as the cephalopods.
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[sinister music playing]
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The largest,
with a shell eight meters long,
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are Cameroceras.
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The trilobite is dwarfed
by this towering hunter.
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00:19:42,431 --> 00:19:45,392
But it's not their size
that makes them such a threat.
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[trilobite squeaks]
200
00:19:50,814 --> 00:19:55,360
Cameroceras have evolved
a new way to catch their prey...
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even when they can't see it.
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[ominous music playing]
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00:20:08,957 --> 00:20:13,837
Because in these waters,
they hunt using not just sight,
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but touch.
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All the trilobite can do
is try to stay out of reach.
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00:20:39,613 --> 00:20:41,615
[ominous music fades]
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[dramatic music playing]
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00:20:52,417 --> 00:20:53,877
With a scissor-like beak...
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[crunching]
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...able to slice through the toughest armor,
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Cameroceras dominate these seas.
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00:21:05,138 --> 00:21:08,308
Although, there is
another important new arrival.
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Graced with a look of permanent surprise,
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this is Arandaspis...
215
00:21:23,782 --> 00:21:25,742
an early kind of fish.
216
00:21:26,576 --> 00:21:28,578
[playful music playing]
217
00:21:30,706 --> 00:21:33,000
It hasn't yet evolved a jaw,
218
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so can only suck up the scraps.
219
00:21:40,632 --> 00:21:42,467
But what it has evolved
220
00:21:43,343 --> 00:21:45,804
will change the course of history.
221
00:21:52,561 --> 00:21:58,150
It has a new internal skeleton
that makes it both fast and agile.
222
00:22:00,110 --> 00:22:01,486
A backbone.
223
00:22:03,196 --> 00:22:05,574
And while it may not look like much,
224
00:22:06,158 --> 00:22:10,829
fish like Arandaspis will one day
give rise to all other vertebrates.
225
00:22:11,788 --> 00:22:16,418
Amphibians, reptiles, mammals, and birds.
226
00:22:20,714 --> 00:22:25,469
But for now,
vertebrates are only at the beginning
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of a very, very long journey.
228
00:22:29,598 --> 00:22:31,391
[music ends]
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{\an8}[tense ambient music playing]
230
00:22:47,616 --> 00:22:52,704
Twenty million years later,
life faced one of its greatest challenges...
231
00:22:52,788 --> 00:22:54,790
[rumbling]
232
00:22:56,124 --> 00:22:58,126
[howling wind]
233
00:22:59,252 --> 00:23:02,881
...as the climate suddenly began to cool...
234
00:23:04,299 --> 00:23:06,259
[thunder rumbles]
235
00:23:08,512 --> 00:23:12,307
...a development that was to have
dire consequences.
236
00:23:14,434 --> 00:23:16,436
[suspenseful music playing]
237
00:23:32,035 --> 00:23:36,706
Little by little,
the sea started to freeze.
238
00:23:39,835 --> 00:23:41,378
[suspenseful music continues]
239
00:23:52,722 --> 00:23:55,934
For the inhabitants
of Earth's once tropical waters,
240
00:23:57,436 --> 00:24:00,105
this was a catastrophe.
241
00:24:04,860 --> 00:24:06,862
[music fades]
242
00:24:09,114 --> 00:24:10,866
[mournful vocalizing]
243
00:24:19,040 --> 00:24:22,794
The shallow seas
became a frozen graveyard.
244
00:24:26,673 --> 00:24:29,885
The world's first mass extinction.
245
00:24:29,968 --> 00:24:31,970
[mournful vocalizing continues]
246
00:24:41,188 --> 00:24:46,693
The fatal freeze was caused
by a 60% drop in carbon dioxide.
247
00:24:49,946 --> 00:24:52,574
Without this greenhouse gas to warm it,
248
00:24:52,657 --> 00:24:55,410
the planet was plunged into an ice age.
249
00:25:01,917 --> 00:25:05,754
One that would last for 200,000 years.
250
00:25:06,713 --> 00:25:08,715
[sorrowful music playing]
251
00:25:15,847 --> 00:25:20,101
At its peak, almost half the world
was covered in ice,
252
00:25:21,019 --> 00:25:26,608
causing the demise of 85% of all life,
253
00:25:27,651 --> 00:25:31,488
lost from our family tree forever.
254
00:25:38,662 --> 00:25:40,664
With the tropical shallows gone,
255
00:25:40,747 --> 00:25:44,501
the few survivors were those
who could head to deeper waters.
256
00:25:52,133 --> 00:25:54,261
Animals like the nautilus,
257
00:25:54,344 --> 00:25:57,514
a smaller relative
of the giant Cameroceras.
258
00:26:04,688 --> 00:26:07,941
It first evolved
hundreds of millions of years ago,
259
00:26:08,692 --> 00:26:10,819
but still exists today.
260
00:26:14,322 --> 00:26:19,452
It owes its success
to the deep ocean's unchanging nature.
261
00:26:21,371 --> 00:26:26,251
Below 600 meters,
the temperature rarely fluctuates,
262
00:26:26,334 --> 00:26:29,212
making it a sanctuary of stability.
263
00:26:32,007 --> 00:26:33,925
When the Ice Age struck,
264
00:26:35,010 --> 00:26:38,221
all kinds of animals
headed into the abyss.
265
00:26:40,807 --> 00:26:44,477
But it's the cephalopods who have thrived.
266
00:26:46,479 --> 00:26:48,607
[majestic music playing]
267
00:26:52,193 --> 00:26:55,655
Today, many still haunt the deep sea...
268
00:26:58,783 --> 00:27:01,953
including octopus and squid.
269
00:27:08,251 --> 00:27:13,131
Their gelatinous bodies are unaffected
by the deep's immense pressure.
270
00:27:17,260 --> 00:27:22,682
And super senses
let them find their way in the dark.
271
00:27:27,145 --> 00:27:29,439
No longer constrained by shells,
272
00:27:29,939 --> 00:27:34,486
they've evolved
into almost every size and shape.
273
00:27:42,535 --> 00:27:46,122
But this pitch-black world
isn't theirs alone.
274
00:27:51,211 --> 00:27:55,048
Arthropods, like this spider crab,
live here too...
275
00:27:58,093 --> 00:28:00,720
feeling their way across the ocean floor.
276
00:28:04,474 --> 00:28:06,935
Alongside them, the vertebrates.
277
00:28:09,854 --> 00:28:14,192
With little food on offer,
down here, they're rare.
278
00:28:18,113 --> 00:28:22,742
Only around 10% of all fish today
live in the deep.
279
00:28:26,788 --> 00:28:29,165
This is not a place they excel...
280
00:28:31,626 --> 00:28:37,590
unlike the cephalopods, who have become
the deep's near-perfect predators.
281
00:28:45,515 --> 00:28:48,810
Something this shrimp may soon discover.
282
00:28:48,893 --> 00:28:50,895
[quiet, suspenseful music playing]
283
00:29:01,823 --> 00:29:06,745
All around it, the water twinkles
with bioluminescent plankton.
284
00:29:09,330 --> 00:29:14,419
Any disturbance, and for the briefest
of moments, they light up.
285
00:29:20,800 --> 00:29:22,427
But the shrimp has company.
286
00:29:27,515 --> 00:29:29,434
A half-concealed squid
287
00:29:30,435 --> 00:29:32,103
is watching the show.
288
00:29:34,939 --> 00:29:39,778
Its large eyes allow it to see
exceptionally well in the dark.
289
00:29:39,861 --> 00:29:41,821
[tense music playing]
290
00:29:49,871 --> 00:29:51,831
Picking out the dots of light,
291
00:29:52,540 --> 00:29:55,335
it can follow every move the shrimp makes.
292
00:29:57,837 --> 00:30:01,257
All it needs is the right moment.
293
00:30:03,885 --> 00:30:05,887
[tense music continues]
294
00:30:22,320 --> 00:30:24,614
The shrimp never saw it coming.
295
00:30:34,499 --> 00:30:36,751
With such extraordinary senses,
296
00:30:37,377 --> 00:30:43,258
perhaps it's no surprise that squid
have mastered this cold, dark world.
297
00:30:45,969 --> 00:30:48,972
{\an8}But for those who lived
back in the Ice Age,
298
00:30:49,514 --> 00:30:51,891
{\an8}things were beginning to heat up.
299
00:30:52,642 --> 00:30:54,644
{\an8}[rumbling]
300
00:30:54,727 --> 00:30:56,729
{\an8}[solemn music playing]
301
00:30:59,607 --> 00:31:01,609
{\an8}[ice creaking]
302
00:31:05,154 --> 00:31:08,408
200,000 years after the big freeze,
303
00:31:10,451 --> 00:31:13,872
there appeared in the ice a vein of blue.
304
00:31:13,955 --> 00:31:16,124
[majestic music playing]
305
00:31:19,127 --> 00:31:20,295
Water.
306
00:31:22,589 --> 00:31:26,009
Carbon dioxide levels had bounced back,
307
00:31:27,719 --> 00:31:30,889
causing global temperatures to rise.
308
00:31:31,764 --> 00:31:34,309
The great melt had begun.
309
00:31:36,519 --> 00:31:40,398
Slow at first,
the thaw rapidly gathered pace.
310
00:31:50,658 --> 00:31:55,538
Before long,
glaciers hundreds of meters tall
311
00:31:55,622 --> 00:31:58,249
cascaded into the warming seas.
312
00:32:03,296 --> 00:32:05,381
[rousing vocalizing]
313
00:32:07,884 --> 00:32:09,344
Within a few millennia,
314
00:32:10,011 --> 00:32:14,307
almost half the planet's ice had melted.
315
00:32:15,600 --> 00:32:19,771
Within a few more, it had entirely gone.
316
00:32:26,194 --> 00:32:29,072
For those who had sought refuge
in the deep,
317
00:32:29,155 --> 00:32:31,699
now was a chance to head back up.
318
00:32:34,243 --> 00:32:36,245
[mysterious music playing]
319
00:32:39,624 --> 00:32:42,251
Off the coast of modern-day Australia,
320
00:32:43,586 --> 00:32:47,006
this is a young giant cuttlefish.
321
00:32:48,758 --> 00:32:51,386
Like his Ice Age ancestors,
322
00:32:51,469 --> 00:32:54,555
he's come to the shallows
in search of a mate.
323
00:33:00,395 --> 00:33:02,689
But others have got here first...
324
00:33:02,772 --> 00:33:05,191
[sinister music playing]
325
00:33:07,402 --> 00:33:10,029
...including an alpha male...
326
00:33:13,199 --> 00:33:15,910
jealously protecting his chosen partner.
327
00:33:20,081 --> 00:33:23,584
And he does not intend to share.
328
00:33:30,508 --> 00:33:33,803
But the smaller male isn't deterred.
329
00:33:35,888 --> 00:33:38,933
Instead, he bides his time
330
00:33:40,393 --> 00:33:41,519
and watches
331
00:33:43,479 --> 00:33:46,607
as a new male enters the arena...
332
00:33:48,776 --> 00:33:50,862
and signals his intention...
333
00:33:53,197 --> 00:33:54,907
to challenge the alpha.
334
00:33:56,159 --> 00:33:58,536
[tense music playing]
335
00:34:02,165 --> 00:34:06,753
With neither backing down,
a fight is inevitable...
336
00:34:06,836 --> 00:34:09,255
[dramatic music playing]
337
00:34:14,510 --> 00:34:18,473
...allowing the young male to make his move.
338
00:34:18,556 --> 00:34:20,099
[whimsical music playing]
339
00:34:20,183 --> 00:34:22,351
[dramatic music playing]
340
00:34:26,397 --> 00:34:30,026
As he approaches,
he tucks in his tentacles
341
00:34:30,985 --> 00:34:32,695
and changes color...
342
00:34:34,906 --> 00:34:36,657
to perfectly mimic
343
00:34:38,034 --> 00:34:39,368
a female.
344
00:34:42,622 --> 00:34:44,999
Using brain, not brawn,
345
00:34:45,541 --> 00:34:47,919
he sneaks straight in.
346
00:34:49,837 --> 00:34:51,839
[whimsical music playing]
347
00:34:52,548 --> 00:34:54,008
[music ends]
348
00:34:56,886 --> 00:35:01,474
The alpha now thinks
he's guarding not one female...
349
00:35:04,477 --> 00:35:05,645
but two.
350
00:35:10,316 --> 00:35:13,611
He's unaware
that this sly young interloper
351
00:35:14,487 --> 00:35:18,032
is mating with his chosen partner.
352
00:35:19,283 --> 00:35:21,285
[tranquil music playing]
353
00:35:32,630 --> 00:35:36,759
Their exceptional intelligence
and remarkable senses
354
00:35:36,843 --> 00:35:41,430
have helped cephalopods
colonize every ocean on Earth.
355
00:35:50,982 --> 00:35:52,692
Yet, in the shallows,
356
00:35:52,775 --> 00:35:57,238
they are rarely the top predators
their towering ancestors once were...
357
00:36:01,159 --> 00:36:03,619
because in the ancient seas,
358
00:36:04,912 --> 00:36:08,249
there was to be a changing of the guard.
359
00:36:08,332 --> 00:36:10,376
[suspenseful music playing]
360
00:36:22,430 --> 00:36:25,391
Seventy million years
after the great melt,
361
00:36:25,474 --> 00:36:28,561
in a period known as the Devonian,
362
00:36:28,644 --> 00:36:31,314
the vertebrates made their move.
363
00:36:31,397 --> 00:36:33,399
[sinister music playing]
364
00:36:37,737 --> 00:36:40,489
This is Dunkleosteus...
365
00:36:43,284 --> 00:36:46,787
a descendant of the tiny Arandaspis.
366
00:36:49,582 --> 00:36:54,503
But at nine meters long,
this fish is no underdog.
367
00:36:59,592 --> 00:37:04,764
Even its young, barely half its size,
are fearsome predators.
368
00:37:09,435 --> 00:37:13,898
And this juvenile
has spotted something out in the blue.
369
00:37:17,360 --> 00:37:18,569
Ammonoids,
370
00:37:19,820 --> 00:37:23,991
close relatives
of today's deep-sea nautilus.
371
00:37:25,159 --> 00:37:27,161
[tense music playing]
372
00:37:33,042 --> 00:37:34,585
Being a vertebrate,
373
00:37:34,669 --> 00:37:38,631
Dunkleosteus has the pace
to catch up with them.
374
00:37:40,800 --> 00:37:42,802
[sinister music playing]
375
00:37:45,763 --> 00:37:49,392
But the ammonoids
boast a trick of their own...
376
00:37:51,936 --> 00:37:53,729
...jet propulsion.
377
00:37:55,106 --> 00:37:58,276
Just what it needs
to outmaneuver the young fish.
378
00:37:59,068 --> 00:38:01,070
[dramatic music playing]
379
00:38:06,242 --> 00:38:07,910
As it starts to circle...
380
00:38:10,288 --> 00:38:12,290
the ammonoid does the same...
381
00:38:16,002 --> 00:38:18,004
shielding its body with its shell.
382
00:38:22,174 --> 00:38:24,176
[growling]
383
00:38:25,678 --> 00:38:29,181
Once upon a time,
this defense would have worked.
384
00:38:29,890 --> 00:38:34,020
But Dunkleosteus has a weapon
its tiny ancestors did not.
385
00:38:38,107 --> 00:38:39,358
Jaws.
386
00:38:40,568 --> 00:38:44,113
It can bite down and crush its prey.
387
00:38:49,952 --> 00:38:52,455
As long as it can find the right angle.
388
00:38:52,538 --> 00:38:54,332
[suspenseful music playing]
389
00:39:10,222 --> 00:39:12,099
Luckily for the ammonoid,
390
00:39:12,183 --> 00:39:15,978
the juvenile's jaws are not yet
strong enough to break its shell.
391
00:39:16,771 --> 00:39:18,773
[teeth clacking on shell]
392
00:39:19,482 --> 00:39:22,276
But the adult's are.
393
00:39:28,324 --> 00:39:30,326
[sinister music playing]
394
00:39:35,456 --> 00:39:37,458
[music fades]
395
00:39:37,541 --> 00:39:42,922
The pairing of backbones with jaws
was to prove a winning combination.
396
00:39:44,090 --> 00:39:47,468
So perfect that, from this moment on,
397
00:39:48,135 --> 00:39:52,139
the vertebrates would never look back.
398
00:39:53,307 --> 00:39:55,309
[rousing music playing]
399
00:40:02,525 --> 00:40:05,986
Today, there are
more than 30,000 species of fish.
400
00:40:11,033 --> 00:40:14,578
Forty times as many as the cephalopods.
401
00:40:22,545 --> 00:40:24,880
While their variety is remarkable...
402
00:40:27,258 --> 00:40:30,136
each still has that perfect pairing.
403
00:40:33,055 --> 00:40:35,391
Backbones give them speed and power...
404
00:40:38,060 --> 00:40:39,645
no matter their size.
405
00:40:43,315 --> 00:40:44,650
While jaws
406
00:40:45,484 --> 00:40:46,986
give them bite.
407
00:40:50,698 --> 00:40:52,950
But there is more to jaws than that.
408
00:40:55,411 --> 00:40:57,997
Some fish use them to protect their eggs.
409
00:40:58,914 --> 00:41:00,916
[serene music playing]
410
00:41:02,751 --> 00:41:05,087
Others to attract a mate.
411
00:41:12,720 --> 00:41:15,681
Then there's the sarcastic fringehead.
412
00:41:16,390 --> 00:41:18,142
{\an8}[playful music playing]
413
00:41:21,437 --> 00:41:24,148
He doesn't just use his to catch crabs.
414
00:41:33,157 --> 00:41:38,370
He also uses them for one of the most
intimidating displays in nature...
415
00:41:41,916 --> 00:41:44,793
to rid his patch of rivals.
416
00:41:53,260 --> 00:41:57,306
For these fish, size is everything.
417
00:42:07,775 --> 00:42:09,860
[music intensifies]
418
00:42:19,328 --> 00:42:20,871
[music fades]
419
00:42:21,539 --> 00:42:25,501
Big jaws have let this fringehead
rule his strip of seafloor,
420
00:42:26,752 --> 00:42:33,217
but they've also allowed a more infamous
group of fish to rule the waves.
421
00:42:33,300 --> 00:42:35,261
[ominous music playing]
422
00:42:40,641 --> 00:42:44,770
They first appeared
more than 400 million years ago
423
00:42:45,729 --> 00:42:48,607
and have been feared ever since.
424
00:42:48,691 --> 00:42:50,693
[stabbing string music playing]
425
00:42:52,820 --> 00:42:54,822
[music intensifies]
426
00:42:54,905 --> 00:42:55,905
They are
427
00:42:57,449 --> 00:42:58,617
the sharks.
428
00:43:03,038 --> 00:43:06,166
To the winning combination
of backbone and jaws,
429
00:43:07,501 --> 00:43:10,087
they've added senses so sharp
430
00:43:10,170 --> 00:43:13,632
they can detect prey
from hundreds of meters away.
431
00:43:16,760 --> 00:43:20,347
With many also boasting size and strength,
432
00:43:21,390 --> 00:43:23,517
they are as close to perfection
433
00:43:24,518 --> 00:43:27,438
as an ocean predator can get.
434
00:43:37,531 --> 00:43:39,533
[tense music playing]
435
00:43:41,160 --> 00:43:43,621
In the sea off Western Australia,
436
00:43:44,204 --> 00:43:47,249
these fish are balled together
for protection.
437
00:43:50,336 --> 00:43:52,379
But the sharks hold back...
438
00:43:54,757 --> 00:43:58,344
because they have
a special plan of attack.
439
00:44:05,726 --> 00:44:07,645
Appearing to work as a team,
440
00:44:08,270 --> 00:44:13,233
some of the sharks rise from below
to trap the fish against the surface.
441
00:44:16,820 --> 00:44:18,614
Others come in from the side,
442
00:44:20,324 --> 00:44:23,160
corralling the shoal
away from the open ocean
443
00:44:23,827 --> 00:44:25,537
and into the shallows.
444
00:44:33,629 --> 00:44:35,506
Now numbering in their hundreds,
445
00:44:36,423 --> 00:44:38,175
the sharks play for time...
446
00:44:42,012 --> 00:44:45,057
as their prey get ever more tired.
447
00:44:49,853 --> 00:44:52,022
[sinister music playing]
448
00:44:58,278 --> 00:45:02,366
It's a hunting technique that has been
honed over millions of years.
449
00:45:04,952 --> 00:45:08,539
But the carnage starts
in the blink of an eye.
450
00:45:09,456 --> 00:45:11,709
[dramatic music playing]
451
00:45:29,852 --> 00:45:32,062
[music continues]
452
00:45:44,575 --> 00:45:46,243
[music fades]
453
00:45:51,123 --> 00:45:54,084
Virtually unchanged since the great melt,
454
00:45:55,335 --> 00:45:59,423
sharks are one of
the most successful dynasties in history.
455
00:46:03,927 --> 00:46:08,640
But they owe their rise
to the fall of their greatest rivals.
456
00:46:20,235 --> 00:46:21,904
{\an8}[mysterious music playing]
457
00:46:26,742 --> 00:46:29,036
Back in the ancient seas,
458
00:46:29,119 --> 00:46:33,373
and Dunkleosteus had reigned
for 20 million years.
459
00:46:34,374 --> 00:46:36,418
[sinister music playing]
460
00:46:37,586 --> 00:46:41,673
So vicious a predator
that not even early sharks could compete.
461
00:46:47,554 --> 00:46:51,517
But Dunkleosteus was to suffer
from a devastating quirk of fate...
462
00:46:54,812 --> 00:46:56,814
[mysterious music playing]
463
00:46:57,648 --> 00:46:59,608
...caused by plankton.
464
00:47:02,820 --> 00:47:04,822
Billions of years earlier,
465
00:47:04,905 --> 00:47:07,699
plankton had been the catalyst
for animal life.
466
00:47:11,078 --> 00:47:14,790
But now,
they would almost bring it to an end.
467
00:47:20,003 --> 00:47:22,673
A sudden surge in ocean nutrients
468
00:47:23,257 --> 00:47:27,052
caused the population of plankton
to increase...
469
00:47:30,472 --> 00:47:32,474
on an unprecedented scale.
470
00:47:32,558 --> 00:47:34,560
[ominous music playing]
471
00:47:40,732 --> 00:47:46,697
As it spread through the sunlit shallows,
this thick soup began to rot...
472
00:47:49,575 --> 00:47:52,494
causing the ocean's oxygen to plummet.
473
00:48:02,421 --> 00:48:08,135
Without this critical ingredient for life,
animals started to suffocate.
474
00:48:08,218 --> 00:48:10,220
[mournful music playing]
475
00:48:18,312 --> 00:48:23,775
For those unable to escape the sludge,
there was only one possible outcome.
476
00:48:26,612 --> 00:48:27,946
Extinction.
477
00:48:31,033 --> 00:48:35,370
Dunkleosteus was one of many
to be lost from our planet.
478
00:48:43,045 --> 00:48:45,047
[mournful music continues]
479
00:48:47,090 --> 00:48:51,094
Across the world,
coastlines became littered with the dead.
480
00:49:03,774 --> 00:49:08,028
Only the lucky few,
including early sharks,
481
00:49:08,111 --> 00:49:09,655
were able to survive.
482
00:49:21,917 --> 00:49:27,005
In all, 80% of marine life
was wiped out in this,
483
00:49:27,089 --> 00:49:30,300
the world's second mass extinction.
484
00:49:32,469 --> 00:49:34,471
[music fades]
485
00:49:35,097 --> 00:49:38,976
And yet this is only half the story.
486
00:49:43,480 --> 00:49:46,525
The nutrients that caused
the plankton explosion
487
00:49:48,068 --> 00:49:50,278
didn't start out in the sea.
488
00:49:50,362 --> 00:49:52,364
[uplifting music playing]
489
00:49:53,991 --> 00:49:56,785
They were carried there from the land...
490
00:50:01,623 --> 00:50:07,754
...released by plants during one
of the most amazing events of all time...
491
00:50:15,554 --> 00:50:18,598
...the greening of planet Earth.
492
00:50:19,683 --> 00:50:21,685
[majestic music playing]
493
00:50:24,396 --> 00:50:26,982
What was once a volcanic wasteland
494
00:50:28,316 --> 00:50:32,070
was now overflowing with life.
495
00:50:32,779 --> 00:50:35,282
- [music fades]
- [creatures chirping]
496
00:50:36,450 --> 00:50:40,120
And this new world offered opportunity.
497
00:50:42,622 --> 00:50:44,916
For where plants had paved the way,
498
00:50:45,876 --> 00:50:48,128
animals would follow.
499
00:50:48,211 --> 00:50:50,213
[chirping continues]
500
00:50:51,965 --> 00:50:58,055
And before long,
the race to dominate the land would begin.
501
00:50:59,014 --> 00:51:03,268
- [dramatic music playing]
- [low growling]
502
00:51:06,730 --> 00:51:08,732
[growling, roaring]
503
00:51:08,815 --> 00:51:10,442
[dramatic music intensifies]
504
00:51:10,525 --> 00:51:12,069
[music ends]
505
00:51:13,570 --> 00:51:15,363
[rousing music playing]
40152
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