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Antarctica.

The coldest, the harshest, and
the most remote continent on Earth.

No human being has ever descended into
the depths that surround it. Until now.

The deep ocean is as
challenging to explore as space.

We know more about the surface of Mars than
we do about the deepest parts of our seas.

Now we can dive these uncharted depths
to discover what secrets lie beneath.

Sinking down beside the submerged wall of
an iceberg, we enter an unforgiving world.

These waters are the coldest on Earth.

As we descend into the deep,
the pressure increases relentlessly.

And the light from
above all but disappears.

Yet, incredibly,

there is life here.

We might have expected
that deep beneath the surface

of the polar seas, the
waters would be truly barren.

But in fact, we find life here
in unimaginable abundance.

Nor is such great abundance
confined to Antarctic waters.

Currents carry this
richness into the depths

of almost every ocean
around the world.

Astonishingly, in the deep sea, there is
more life than anywhere else on Earth.

The Sunlight Fades, and the Seas Darken

Here in the Pacific,
200 meters down, we

enter an ever -changing
sea. An alien world.

The Twilight Zone. A sea of eternal gloom.

There are strange creatures
here. A pyrosome. A tube of

jelly two meters long that
dwarfs a visitor from above. An

oceanic whitetip shark.

Only a tiny amount of
light filters down this far.

Survival here means making
the most of every last glimmer.

A swordfish.

Its eyes are as big as tennis balls
to help it see in the perpetual dusk.

A squid. But this is one that
lives only here. Its right eye

looks permanently downwards.
But its left eye is much bigger

and trained upwards
to detect the silhouettes

of prey swimming
nearer the surface.

No wonder it's nicknamed
the cock-eyed squid.

And even stranger. This is barrel-eye.

A fish with a transparent
head, filled with

jelly so that it can look
up through its skull.

We now know that the
Twilight Zone is a refuge

for an incredible 90%
of all fish in the ocean.

Only at night do vast
shoals of lanternfish

migrate the surface to
feed on tiny plankton.

By day, they retreat back down here.

Humboldt's squid.

Two meters long and 50 kilos in weight.

Like most squid, they're voracious hunters.

There are hundreds of them.

They've found a shoal
of lanternfish, hiding

800 meters down off the
coast of South America.

Their tentacles are full of
fish. Their tentacles are armed

with powerful suckers, with
which they grab their prey.

And when there are no more lanternfish
to be found, they turn on each other.

This squid has caught a
smaller one in its tentacles.

To hide its capture from the rest, it
releases a smoke screen of black ink.

But then an even bigger one challenges it.

And steals its catch.

The Twilight Zone is the
Humboldt squid's favorite hunting

ground. They seldom go
deeper into the world of perpetual

blackness below.

The Midnight Zone.

Two thirds of a mile from the
surface, beyond the reach of the sun.

A giant black void, larger than all the
rest of the world's habitats combined.

There's life here. But not as we know it.

Alien-like creatures produce
dazzling displays of light.

Nearly all animals need to
attract mates and repel predators.

This language of light is so
widespread here, that these

signals are probably the
commonest form of communication on

the entire planet. And yet, we
still know little about them. What are

they?

This is Fang Tooth. It has
the largest teeth for its size of

any fish. There are precious
sensors all over its head and

body, which can detect anything
moving in the surrounding

water. But there's no sign
of anything moving in the

surrounding water.

It's the Midnight Zone's most voracious
fish. But prey use light as a distraction.

A decoy of luminous ink.

Down here, in this blackness, creatures
live beyond the normal rules of time.

Siphonophores are virtually
eternal. They repeatedly clone

themselves. Some eventually
growing longer than a blue

whale.

Down here, it snows.

Continuous clouds of organic
debris drift slowly down from above.

This is food. And a whole variety
of filter feeders depend on it.

Jellyfish.

And delicate sea cucumbers.

The 1% of marine snow they miss
eventually settles on the seafloor.

Over millions of years, it forms
a layer of mud up to a mile thick.

It's an empty plain that covers
half the surface of our planet.

The deep seabed may
at first appear lifeless,

but it's home to a unique
cast of mud-dwellers.

The sea toad. It's a rare
species of sea turtle. This is

an ambush predator with an
enormous mouth and infinite

patience.

This fish has been
living for so long here that

its fins have changed
into something more useful.

Feet.

They help it shuffle about on the seafloor.

The flapjack octopus.

It hovers just above the
surface of the mud as it

delicately sifts through
it, searching for worms.

But it can jet away at
the first sign of danger.

A six-gill shark as big as a great white.
It may not have eaten for an entire year.

It patrols the mud plains
using a minimum amount

of energy. It's a rare
species of sea turtle.

High above, the carcass of a huge
sperm whale is slowly decaying.

This will be a bonanza for the
creatures of the deep. Food. 30 tons of it.

Finally, it settles on the ocean floor.
And its presence is soon detected.

Six-gill sharks have an
exceptionally acute sense of smell.

Just 25 minutes after the whale's
carcass arrives, a six -gill finds it.

Each bite releases blood into the current.

The news that food is here spreads quickly.

Two more ravenous six-gills arrive.

The first one to be
found is a giant sea turtle.

Within 12 hours, there are
seven enormous sharks jostling

with one another as they
compete to tear off mouthfuls.

No one is prepared to back off.

The first one to be
found is a giant sea turtle.

24 hours later, and a third
of the carcass has gone.

The first arrival has gorged
until it's completely full.

This single meal may be enough
to sustain it for a whole year.

Now, the clean-up team arrives.

Spider crabs carrying coral in their hind
legs, presumably as makeshift body armor.

There are rock crabs here,
too. They probably detected the

carcass almost as soon as the
sharks. But they can't move as

fast.

A month on, and over
30 species of scavenger

are clearing away the
last edible fragments.

But now the scavengers are
attracting their own predators.

Scabbard fish, habitually swimming
upright, are picking them off one by one.

Some of the whale's
teeth have been dislodged

as the skeleton
starts to fall apart.

Four months later, there is
nothing left but a few bones.

But even they are food...

for something.

Zombie worms.

They tunnel into the bones
by injecting acid, and so reach

the tiny amounts of fat that
still remain there. It may take

decades, but eventually the
last of the bones will crumble,

and the whole 30-ton carcass
will be destroyed. The bones

will have been recycled.

A whale fall is a temporary
oasis in the desert of the seafloor.

But there are permanent oases here, too.

Rocks projecting above the mud
provide anchorage for deep -sea corals.

As far down as three and
a half miles, there are more

species of coral in the deep
than on shallow tropical reefs.

Without sunlight, they rely solely
on food drifting in the current.

And they grow just a hair's breadth a year.

But some of them can live for 4,000 years.

They, like their
shallow-water relatives,

provide homes for all
kinds of other creatures.

Growing among the corals is one
of the most beautiful of sponges.

This is Venus's flower basket.

These sponges have lodgers, shrimps,

and fish. There are plenty of predators
on the reef, so the shrimps are fortunate.

Both this male and female
were swept into this sponge when

they were tiny larvae, along
with the minute particles of

food on which the sponge feeds.

They found each other and
have been here ever since.

Now they're full-grown, and
the female is carrying eggs.

Once hatched, the larvae will
swim out through the sponge's walls.

But the shrimps will
never leave. They can't.

They're now trapped in the
sponge. They're now far too big

to go out the way they came
in, and no doubt they will live

longer here than they would if they were
wandering about on the reef unprotected.

But how one of the simplest
of all animals, a sponge, is

able to build such a complex
structure to the great benefit

of the shrimps is a
mystery and surely a marvel.

But today, their timeless
world is being reduced to rubble.

As over 100 years ago, however
fishing empties the surface

waters of the seas, trawlers
have started to ransack the

deep.

Now, countless numbers
of the reefs that have

flourished here for
millennia lie in ruins.

Over time, organic matter on the
seafloor slowly decays, producing methane.

And now, the world is in chaos.
The world is in chaos. The world

is in chaos. The world is in
chaos. The world is in chaos.

The world is in chaos. The
world is in chaos. The world is

in chaos. The world is in
chaos. The world is in chaos.

The world is in chaos. The
world is in chaos. The world is

in chaos. The world is in
chaos. The world is in chaos. The

world is in chaos. The world is
in chaos. The world is in chaos.

The world is in chaos.
In the Gulf of Mexico,

these eruptions also
release a super-salty liquid.

Brine.

Five times heavier than seawater, it
accumulates in great pools on the seafloor.

It's difficult to make sense of the site.

A lake of concentrated saltwater, 15
meters deep, at the bottom of the sea.

Around its margin, perhaps
even more strangely, there is a

profusion of life. A lake of
concentrated saltwater, and a

giant rock.

Giant mussels that can live
and grow for a century or more

pack it tightly together,
dwarfing the shrimps and squat

lobsters that feed around them.

Cut-throat eels, scavengers,
come to the shores

of the Brine Lake in
search of something edible.

Some even venture into the
sea and venture into the brine.

Spending too long in it can
send an eel into toxic shock.

Its only hope is to rise above it.

It manages to

escape.

Others are not so lucky.

The brine embarks on its way
as it swarms their bodies, and

the casualties of decades
accumulate around the margins.

But parts of their deep
are even more hostile.

In places, gigantic cracks stretch
for many miles across the ocean floor.

Canyons that plunge
towards the center of the earth.

Scans from survey vessels
make it possible to graphically

reconstruct an image of this
vast submarine landscape.

The deepest of all, at almost seven miles,
is the Mariana Trench in the Pacific Ocean.

Even Mount Everest
could disappear inside it.

Down here, in these
deep ravines, it was once

thought that nothing whatever
could possibly survive.

But there is life even here.

A kind of sea slug.

A so-called sea peak. They
and other simple creatures

managed to survive on the
minuscule amount of food that

drifts down here.

Like this starfish, they
can withstand pressure

equivalent of 50 jumbo jets
stacked on top of one another.

A remote camera probe reveals
the most extraordinary discovery of all.

The ethereal snailfish.

At five miles down, this is the largest and
the deepest living fish so far discovered.

No one imagined that
an animal as complex as

a fish could exist in
such extreme pressures.

From the greatest depths
to the uppermost limit of the

twilight zone, it seems that
there is nowhere in the deep

sea where life of some kind can't survive.

And we now think that the
deep sea may well be one of

the most dangerous and will
be where life on Earth began.

Here, in a world hidden within the
greatest geological feature on Earth.

Running right down the
middle of the world's oceans,

an underwater mountain
range spanning the entire globe.

The mid-ocean ridge.

In the South Pacific, the
ocean floor is being torn apart.

In the South Pacific, the
ocean floor is being torn apart.

Over three-quarters of the planet's
volcanic activity occurs in the deep.

Almost all of it along the
mid-ocean ridge. The deep sea.

But from this titanic
violence come great beaches.

Gases and scalding water
gush up through the crevices.

Minerals condensing from these jets build
up great chimneys. Hydrothermal vents.

This one, 30 meters tall,
has been named Godzilla.

Astonishingly, we now know that they
hold as much life as tropical rainforests.

In places, half a million
individual animals

are crammed into a
single square meter.

They depend entirely for
their food on bacteria. And they

feed on chemicals dissolved
in the searingly hot fluid.

Crabs consume the bacterial
mats that coat their shells.

Others maintain bacterial
cultures actually within their bodies.

Shrimps carry such
cultures in their mouthparts.

But that is a strategy
fraught with danger.

The To provide sustenance
for these microbes, the shrimps

must dash into the hot vents.
And that risks being boiled

alive.

In the last decade, the number of
hydrothermal vents discovered has doubled.

Everyone has its own unique
character and community.

But perhaps the most
important one of all is in

the Atlantic. It has been
named the Lost City.

Within its 60-meter towers, something
truly extraordinary is taking place.

Under extremes of pressure
and temperature, hydrocarbons,

the molecules that are the
basic component of all living

things, are being created spontaneously.

Indeed, many scientists now
believe that life on Earth may

have begun around a vent
like this four billion years ago.

We now know that there are deep
seas on the moons of Jupiter and Saturn.

If life can exist under such
extreme conditions down

here, then surely it could
exist somewhere out there.

The team spent more than a
thousand hours filming in the

deep ocean, mostly from the
research vessel Aluxia and her

twin submersibles Deep Rover and Nadir.

Their most ambitious mission
was to Antarctica, hoping

to film life two-thirds of a
mile down, something never

attempted before.

We honestly do not know what
we're going to find down there.

We're going to a place that
has never been explored. There

could be nothing, there
could be a carpet of life,

there could be anything
in between. Who knows?

It's a huge technical challenge.

The water temperature here can
reach minus 1.8 degrees centigrade.

No one knows for sure how the subs
will cope with this extreme environment.

Just half an hour
into the very first dive,

a puddle is forming
on the floor of the sub.

Orla confirms it's seawater.

They must find the
leak and prepare it fast.

When you look at it from the
shop back up to the surface,

you're kind of thinking about,
are we going to fill up with

water? And if we are,
there's no way out. The

sub pilots are well
drilled for emergencies.

Ralph quickly finds the
flood and fixes it. He made it

all seem absolutely ordinary
and normal and I've got this

coverage, don't you worry.
And within 20 minutes, he did.

The waters of the Antarctic
Sound are potentially rich but

also treacherous. The Sound
is ominously known as Iceberg

Alley. We've got to find a
place where we can get the

submarines down and up safely
without any icebergs coming

along and berthing them
over. I've got a feeling it's going

to be a bit like Game of Space
Invaders. A meter cube of ice

weighs a tonne. You start
sort of grinding that around

the sphere, it's delicate.
It's like a big Faberge egg.

One dive brings them right up to
the underside face of an iceberg.

There are icebergs up there
that are the size of a small car

and then there are icebergs
up there that are the size of

Hyde Park. Enormous.
Conditions here can change in an

instant. The captain radios
down to the subs. I'm worried

about the ice coming down
on you. That's what I'm worried

about. Yeah, Roger that. We've
currently got a couple of big

icebergs coming down the channel and it
looks like they're on a collision course.

The impact of two icebergs
colliding overhead is clearly heard.

That is ice. With icebergs
colliding above and the

weather turning fast, the
subs are quickly recalled.

Once again, their efforts are thwarted.

Finally, after two weeks,
conditions are just right. Once

again, the team attempt their
1,000-metre dive in Iceberg

Alley.

An hour after leaving the
surface, they close in on their goal.

999. 999.

Control, control. That is
Nadir. On bottom, depth 1,000

metres. Roger, depth 1,000
metres. Control out. New record.

First man sub-dive to 1,000
metres in Antarctica. At the

bottom of the ocean, at the
end of the world, the amount of

life they find is astonishing.

But they're equally astonished
to find that, two-thirds of

a mile from the surface,
icebergs are still a danger. Rocks

can drop from them as they melt
and one lands right in front of the sub.

I don't think many people who
are diving subs ever consider

big lumps of rock landing
on them. It's not your normal

risk. If it had hit the sphere,
there's a good chance it

would have put a nice scratch
down it. If something of 10,

15, 20 tonne had hit the sub,
it would completely destroy it.

But over the following dives,
the team learns it's these

very dropstones that enrich
the Antarctic deep sea bed,

creating firm anchor
points for life to thrive.

Proof that the only way to
fully appreciate the complexity

and abundance of life in the
deep is to go there ourselves.

Next time, we travel
to bustling coral reefs.

Here, animals must go
to extraordinary lengths to

get ahead of the competition
in these crowded cities.

For more information, visit www.mooji.org