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Over 60% of our planet
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is covered by ocean
more than a mile deep.
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That, the deep sea,
is by far
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the largest habitat
on Earth,
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and it's
largely unknown.
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Join us on a journey to
the very bottom of the deep sea,
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to an alien world
never revealed before.
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It's home to some of
the strangest animals on Earth.
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Fish flash
in the darkness.
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New species are discovered
on almost every dive.
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More people have
traveled into space
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than have ventured
this deep.
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Come on a journey
into the abyss.
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A sperm whale takes a breath,
its last for over an hour.
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It's about to
leave the warm,
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well-lit surface waters,
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and dive far down
into the cold,
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dark depths
of the deep ocean.
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At the surface,
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it took in air at the same
pressure as we breath it.
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But it's going to
look for food
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at more than
1,000 meters down,
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where pressure is 100 times
that on the surface,
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crushing the whale's lungs
to just 1% of their volume.
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For us to follow
the whale,
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we need the very latest
submersible.
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A reinforced acrylic sphere
with walls 12 centimeters thick
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protects a pilot
and our cameraman
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from the enormous
pressure below,
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and allows the submarine
to dive to just over 900 meters.
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With every passing meter,
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pressure increases,
and sunlight diminishes.
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1,000 feet.
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By 300 meters,
it's already very dark,
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and the temperature of the water
is dropping fast.
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My depth is 1,755.
Temperature is...
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We are entering
the twilight zone,
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a weird world of gloom,
where many animals
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have become completely
transparent.
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In this twilight,
an animal needs to see,
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and yet,
as far as possible,
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must avoid being seen.
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A giant amphipod,
12 centimeters long,
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and almost perfectly
transparent.
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Its head is completely filled
by two huge eyes,
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with which it strains
to detect its prey.
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Another twilight monster,
Phronima,
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the inspiration for
the Alien movies.
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She and her developing
pink offspring
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live like parasites
in the stolen body of a jelly.
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This impressive
cutlery set
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and its huge eyes
make Phronima
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a powerful predator.
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Even really complex animals
have become transparent
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in the twilight zone.
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Squids are among the most
advanced of invertebrates,
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but this one never meets a hard
surface in its entire life,
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so its body need not be
as robust
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as that of its
shallow-water cousins.
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There's a rich variety
of jellies
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that live nowhere else
but in the deep sea.
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Thousands of tiny cilia
propel them
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through a world
without walls.
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Invisible in the gloom,
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they grope blindly
for their prey.
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Comb jellies let out long,
sticky nets
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to catch
passing copepods.
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But the most extensive
death trap
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is set by
siphonophores.
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This pulsating bell is
the head of a colonial jelly
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that can be
40 meters long.
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Millions of tiny stinging cells
drifting through the sea.
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500 meters down,
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00:06:02,896 --> 00:06:05,000
and in even the clearest
tropical waters,
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only the faintest vestige
of the sunlight remains,
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so little that our eyes
can't detect it.
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But others can.
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Survival in
the twilight zone
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is all about seeing
yet not being seen.
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Hatchetfish are masters
of the game of hide and seek.
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They have the large,
sensitive eyes
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needed for
seeking prey,
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but their bodies
are flat.
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And their sides
are highly silvered.
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Head-on, they are just visible,
thin though they are.
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But as soon as they turn,
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their mirrored sides
reflect the remnants
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of blue light
from the surface,
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and they disappear
into the gloom.
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Viewed from the side,
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whole shoals can hide
in this way.
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But what about
from below?
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The tubular eyes
of many of the predators,
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even in this gloom,
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are able to distinguish
their prey silhouetted against
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the scarcely detectable glimmer
of light from above.
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Hatchetfish, however,
have a way of confusing any eyes
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that might be searching
for them from below.
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Their bellies carry rows
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of light-producing cells
called "photophores."
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They can use these
to exactly match
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the changing color of light
from the surface far above.
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This counter-shading
breaks up their silhouette,
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making them almost invisible
from below--
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almost.
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But these are
no ordinary eyes.
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The enormous yellow lenses
enable their owner
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to distinguish
between light
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produced by photophores
and sunlight.
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So, one device for escape
is countered by another
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equally subtle one for attack
in an evolutionary arms race
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that has been waged
for millions of years.
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Let's begin.
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My dog is one of us.
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You and me, girl.
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Home protection?
Hunting.
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Out here,
most folks let things go.
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I guess I'm not
most folks.
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I want to live.
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Are you prepared to kill?
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Yes.
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One of us is not
leaving this island.
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You ready?
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Descend below 1,000 meters,
and you enter the dark zone.
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No sunlight whatsoever
penetrates this deep.
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The temperature
of the water
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has dropped below
4 degrees centigrade.
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The pressure is more than
100 times that at the surface.
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Life becomes
ever more sparse.
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It's a dark,
dangerous world.
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Relative to body size,
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these are the largest teeth
in the ocean.
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They're so big that their owner
can't even close its mouth.
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They belong to
the fangtooth.
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Unlike most deep-sea fish,
this has powerful muscles,
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and is
an aggressive hunter.
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With food in such short supply
at this depth,
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dark-zone predators
have to be able to deal with
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a meal of almost
any size.
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Many animals here are dark red,
like this deep-sea jelly.
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Caught in the lights
of the submersible,
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it's a spectacular
firework display of color.
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Normally, no red light
penetrates as deep as this,
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so animals with
red pigment
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appear completely black
down here,
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perfectly concealed.
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Predators here, however,
don't just rely on vision.
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Many have tiny eyes.
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Instead, their thin rod-like
bodies are lined with organs
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sensitive to tiny movements
in the water.
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This monster,
half a meter across,
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is a hairy angler.
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This is the first time
it's been seen.
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It's covered with hundreds
of sensitive antennae,
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each capable of detecting
the movements
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of any prey
careless enough to stray
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too close to this
motionless predator.
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But this surely must be
the strangest of all
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the deep-sea fish
yet discovered.
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A highly sensitive
meter-long tail
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hangs down
from the head
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that makes up
a quarter of its body.
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Its eyes are tiny,
but its mouth is truly enormous.
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It's called the "gulper eel"
because it can engulf a meal
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of almost any size.
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Hanging motionless
in mid-water,
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its enormous gape enables it
to deal with passing prey,
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whether it's small
or large.
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Gulper eels can swallow prey
as big as themselves,
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which is very useful in a world
where you never know
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when the next meal
is coming along.
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Even in the dark zone,
there is some light.
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Turn off
the submersible headlights,
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and you see a pyrotechnic
display outside.
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These lights are created
by animals.
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This is bioluminescence.
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A deep-sea anglerfish
flashes in the darkness.
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The light is generated
by bacteria
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that live permanently
inside the lure,
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which attracts prey
to these murderous teeth.
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There are all sorts of lures
out in the darkness.
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"Come into my mouth,
little fish."
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And what is the purpose
of this lure,
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suspended on a long rod,
way below
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its owner's terrifying
set of teeth?
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It's difficult to be sure,
but then, this monster does have
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another giant flashing lure
much closer to its mouth.
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These fish are called "anglers"
because they use their lures
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in much the same way
as fly fishermen
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use their imitation flies.
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For a hunting squid
with huge eyes,
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this glimmer
is intriguing.
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It might just be food.
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A satisfying meal
for a fish
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with a highly
extendible stomach.
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Attracting a mate
in this endless darkness
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00:15:17,517 --> 00:15:19,965
can be even harder
than finding food.
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00:15:25,551 --> 00:15:28,206
Flashing lures may be helpful
in doing this.
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00:15:28,241 --> 00:15:30,793
Certainly only
female anglers have them.
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00:15:36,379 --> 00:15:39,689
The tiny males are just a tenth
the size of the females.
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Their only purpose
is somehow
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to find a mate
in the darkness.
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She releases chemicals
into the water,
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which the males scent
with a special white organ
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00:15:49,931 --> 00:15:51,482
in front of their eyes.
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00:15:55,965 --> 00:15:59,413
Having found a partner,
the male bites at her belly
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00:15:59,448 --> 00:16:01,448
with specially
designed teeth.
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00:16:06,241 --> 00:16:09,275
He needs to get
permanently attached.
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00:16:13,172 --> 00:16:14,827
Within a matter of weeks,
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00:16:14,862 --> 00:16:17,482
the male is completely fused
to the female,
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00:16:17,517 --> 00:16:20,689
and there he will stay
for the rest of his life.
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00:16:20,724 --> 00:16:22,862
Her blood
circulating in his body
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00:16:22,896 --> 00:16:25,896
provides him with
all the sustenance he needs.
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00:16:25,931 --> 00:16:28,379
In return,
she gets a continuous,
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00:16:28,413 --> 00:16:30,551
reliable supply
of sperm--
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00:16:30,586 --> 00:16:32,344
a brilliant solution
to the problem
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00:16:32,379 --> 00:16:35,965
of finding a mate in the vast
emptiness of the deep sea.
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00:16:46,724 --> 00:16:50,517
To help in the constant battle
between predators and prey,
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00:16:50,551 --> 00:16:54,241
some fish in the dark zone
have developed headlights.
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00:17:01,103 --> 00:17:04,689
These light-producing
photophores beneath their eyes
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00:17:04,724 --> 00:17:10,206
may be used to search out prey
in the darkness.
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00:17:10,241 --> 00:17:12,862
Most bioluminescence
in the deep sea
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00:17:12,896 --> 00:17:15,482
is blue or greenish-blue,
224
00:17:15,517 --> 00:17:19,448
but a very few predatory fish
produce red light.
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00:17:24,862 --> 00:17:30,758
With this, red prey becomes
obvious in the darkness.
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00:17:30,793 --> 00:17:33,034
Red light is rare
down here,
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00:17:33,068 --> 00:17:35,620
and most animal eyes
can't see it.
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Only these fish
can do so.
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00:17:38,655 --> 00:17:41,172
This gives them
a sniper scope,
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00:17:41,206 --> 00:17:43,862
a headlight invisible
to their targets.
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00:17:49,655 --> 00:17:53,241
This copepod, un-alarmed,
takes no avoiding action.
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00:18:01,344 --> 00:18:05,620
Bioluminescence is useful
in escape as well as attack.
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A shrimp
senses a threat.
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00:18:18,206 --> 00:18:22,482
It spins in the water,
releasing a bioluminescent glue.
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00:18:26,068 --> 00:18:28,034
This acts like
a burglar alarm,
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00:18:28,068 --> 00:18:29,689
startling
the attacking fish,
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00:18:29,724 --> 00:18:31,827
and leaving it illuminated
in the dark,
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00:18:31,862 --> 00:18:34,068
and vulnerable
to its own predators.
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00:18:38,241 --> 00:18:40,620
These twinkling lights
in the darkness
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00:18:40,655 --> 00:18:42,551
are produced
by copepods.
241
00:18:45,310 --> 00:18:46,896
They probably
flash like this
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00:18:46,931 --> 00:18:49,034
to communicate
with one another,
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00:18:49,068 --> 00:18:51,137
and confuse
their predators.
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00:18:55,827 --> 00:18:57,827
The most sensitive eyes
in the ocean
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00:18:57,862 --> 00:19:02,517
belong to an ostracod
called "Gigantocypris."
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00:19:02,551 --> 00:19:04,137
It's the size of a pea,
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00:19:04,172 --> 00:19:08,517
but that's enormous
for an ostracod.
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00:19:08,551 --> 00:19:12,137
Copepods are a favorite prey,
and it actively searches for
249
00:19:12,172 --> 00:19:13,724
their flashes
in the darkness.
250
00:19:18,689 --> 00:19:21,310
But this copepod
has a way of confusing
251
00:19:21,344 --> 00:19:22,965
a hunting Gigantocypris.
252
00:19:28,103 --> 00:19:33,620
It discharges a packet
of bioluminescent liquid.
253
00:19:33,655 --> 00:19:36,551
The flash is delayed,
like a depth charge.
254
00:19:40,551 --> 00:19:42,724
Spinning, confused
in the water,
255
00:19:42,758 --> 00:19:45,586
Gigantocypris chases
after the flashes.
256
00:19:54,068 --> 00:19:58,241
And the copepod slips away,
unseen, into the darkness.
257
00:20:07,241 --> 00:20:10,586
The ultimate bioluminescent
defense mechanism
258
00:20:10,620 --> 00:20:12,793
has to be the light show
created by
259
00:20:12,827 --> 00:20:15,413
the deep-sea jellyfish
periphylla.
260
00:20:26,344 --> 00:20:30,000
That, presumably, is the way
it scares away its enemies.
261
00:20:45,689 --> 00:20:49,896
These bright lights are all
produced by firefly squid.
262
00:20:49,931 --> 00:20:53,379
Normally, they live way down
at around 300 meters,
263
00:20:53,413 --> 00:20:57,620
beyond the reach of these
Japanese fishermen's nets.
264
00:20:57,655 --> 00:20:59,275
But for a few months
each spring,
265
00:20:59,310 --> 00:21:01,655
they come to the surface
every night.
266
00:21:05,413 --> 00:21:08,655
The brightest lights come from
the bioluminescent tips
267
00:21:08,689 --> 00:21:10,551
of their two
front tentacles.
268
00:21:10,586 --> 00:21:13,379
But it's only in the dark
of the deep sea that you can
269
00:21:13,413 --> 00:21:15,517
really appreciate
the full complexity
270
00:21:15,551 --> 00:21:17,862
of their displays.
271
00:21:17,896 --> 00:21:19,724
It's not just
their tentacles,
272
00:21:19,758 --> 00:21:22,965
but their whole bodies,
that are covered in photophores.
273
00:21:27,137 --> 00:21:29,724
The exact function
is not clear.
274
00:21:29,758 --> 00:21:32,620
The bright tentacle tips
may be for attracting mates
275
00:21:32,655 --> 00:21:34,655
or dazzling predators.
276
00:21:34,689 --> 00:21:36,862
The rest may be
camouflage,
277
00:21:36,896 --> 00:21:39,344
providing counter-shading
for the squid
278
00:21:39,379 --> 00:21:42,172
as they journey up into
the twilight zone.
279
00:21:45,137 --> 00:21:47,862
Every night
in the season,
280
00:21:47,896 --> 00:21:49,689
hundreds of thousands
of squid
281
00:21:49,724 --> 00:21:51,655
journey up into
shallow water to spawn.
282
00:21:57,655 --> 00:22:00,000
Before dawn,
they will return to the depths,
283
00:22:00,034 --> 00:22:02,482
leaving their eggs to develop
in the shallows.
284
00:22:13,931 --> 00:22:17,620
The daily cycle of the sun
has a profound influence
285
00:22:17,655 --> 00:22:20,310
on life in
the deep ocean.
286
00:22:20,344 --> 00:22:23,620
As the sun sets, it triggers
the largest migration
287
00:22:23,655 --> 00:22:26,862
of living organisms
on our planet.
288
00:22:26,896 --> 00:22:29,931
1,000 million tons
of animals
289
00:22:29,965 --> 00:22:32,517
travel up from the dark zone
into richer,
290
00:22:32,551 --> 00:22:34,655
shallower water
every night.
291
00:22:38,068 --> 00:22:40,413
Tiny grazers
are first up,
292
00:22:40,448 --> 00:22:42,724
searching for
the microscopic plants
293
00:22:42,758 --> 00:22:47,379
that only grow in shallow,
sunlit waters.
294
00:22:47,413 --> 00:22:49,862
Predators follow
the grazers.
295
00:22:52,689 --> 00:22:54,931
An enormous variety
of different animals
296
00:22:54,965 --> 00:22:58,172
join the convoy,
or feed off it as it passes.
297
00:23:04,896 --> 00:23:07,000
Many will travel up
hundreds of meters
298
00:23:07,034 --> 00:23:09,551
towards the surface,
and then, at dawn,
299
00:23:09,586 --> 00:23:12,379
finding themselves
at greater risk from predators,
300
00:23:12,413 --> 00:23:15,482
the visitors return to the safer
darkness of the depths.
301
00:23:23,931 --> 00:23:26,586
The sun's rays only have
a direct effect
302
00:23:26,620 --> 00:23:29,482
in the top hundred meters,
or so, of the ocean.
303
00:23:29,517 --> 00:23:32,862
It's only here that
photosynthesis can take place,
304
00:23:32,896 --> 00:23:35,379
and coral reefs
can flourish.
305
00:23:35,413 --> 00:23:38,000
Leave this thin,
rich slice of life,
306
00:23:38,034 --> 00:23:40,310
and travel over
the outer face of the reef,
307
00:23:40,344 --> 00:23:44,034
and you quickly enter
a far more demanding world.
308
00:23:52,896 --> 00:23:54,793
Below 150 meters,
309
00:23:54,827 --> 00:23:57,448
photosynthesis
becomes impossible.
310
00:23:59,241 --> 00:24:03,034
You find no plants,
just animals.
311
00:24:05,413 --> 00:24:09,241
Here, the animals are adapted
to catch marine snow--
312
00:24:09,275 --> 00:24:11,517
particles of dead animals
and plants
313
00:24:11,551 --> 00:24:13,655
that drift down
from above.
314
00:24:13,689 --> 00:24:15,724
So, they depend,
second-hand,
315
00:24:15,758 --> 00:24:17,724
on the energy
captured from the sun
316
00:24:17,758 --> 00:24:20,413
by organisms living in
the surface waters.
317
00:24:29,827 --> 00:24:32,034
Traveling close to
the sea floor,
318
00:24:32,068 --> 00:24:34,965
we're going to take a journey
to the very bottom
319
00:24:35,000 --> 00:24:37,827
of the deep sea,
320
00:24:37,862 --> 00:24:41,551
to a world completely separate
from the mid-water above.
321
00:24:51,068 --> 00:24:54,758
At around 300 meters,
the drop-off levels out,
322
00:24:54,793 --> 00:24:57,482
and we move out onto
the continental slope.
323
00:25:00,413 --> 00:25:04,103
This stretches for about
150 miles from the coast,
324
00:25:04,137 --> 00:25:06,137
sloping in
a gentle gradient
325
00:25:06,172 --> 00:25:09,655
down to a maximum depth
of 4,000 meters.
326
00:25:12,000 --> 00:25:16,482
Water temperatures down here
drop below 4 degrees centigrade,
327
00:25:16,517 --> 00:25:20,724
and the pressure can reach up to
400 times that of the surface.
328
00:25:27,862 --> 00:25:29,965
Without the lights
of the submersible,
329
00:25:30,000 --> 00:25:32,517
it would be
completely dark.
330
00:25:32,551 --> 00:25:34,482
The water
is crystal clear
331
00:25:34,517 --> 00:25:37,137
because there's so little
organic matter.
332
00:25:37,172 --> 00:25:39,620
Only 3%
of the potential food
333
00:25:39,655 --> 00:25:42,862
in the surface waters
reaches the continental slope.
334
00:25:47,689 --> 00:25:51,103
At first sight,
it appears a lifeless desert.
335
00:25:51,137 --> 00:25:52,620
But take a closer look,
336
00:25:52,655 --> 00:25:56,000
and you notice a network
of tracks and trails.
337
00:25:56,034 --> 00:25:58,758
There is life,
even down here.
338
00:26:02,724 --> 00:26:04,931
These animals
would die immediately
339
00:26:04,965 --> 00:26:07,103
if brought to the surface
in nets,
340
00:26:07,137 --> 00:26:09,448
so you can only see them
behaving normally
341
00:26:09,482 --> 00:26:11,241
from submersibles.
342
00:26:11,275 --> 00:26:13,310
Many are new
to science.
343
00:26:17,758 --> 00:26:19,586
The deep sea floor
is dominated
344
00:26:19,620 --> 00:26:22,517
by echinoderms--
sea cucumbers,
345
00:26:22,551 --> 00:26:26,344
brittle stars,
and sea urchins.
346
00:26:26,379 --> 00:26:28,379
There are literally
millions of them
347
00:26:28,413 --> 00:26:31,000
marching across the seabed,
hoovering up
348
00:26:31,034 --> 00:26:35,103
any edible particles there
might be in the sediment.
349
00:26:35,137 --> 00:26:38,310
They come in all sorts
of shapes and sizes,
350
00:26:38,344 --> 00:26:40,379
and though they are
very thinly spread,
351
00:26:40,413 --> 00:26:43,482
the deep ocean floor is so vast
that these are among
352
00:26:43,517 --> 00:26:47,241
the most numerous animals
on the planet.
353
00:26:47,275 --> 00:26:50,000
Their spikes are good
for locomotion and defense,
354
00:26:50,034 --> 00:26:53,413
but perhaps not quite so good
when it comes to mating.
355
00:26:57,172 --> 00:27:00,310
Finding a mate
in this largely empty sea floor
356
00:27:00,344 --> 00:27:04,551
could be a problem, so some
urchins stay together on herds,
357
00:27:04,586 --> 00:27:06,310
to be sure that
they're never too far
358
00:27:06,344 --> 00:27:07,896
from a potential partner.
359
00:27:12,172 --> 00:27:14,931
Rocky outcrops provide
good anchorage for animals
360
00:27:14,965 --> 00:27:18,344
that rely on food
that might drift past.
361
00:27:18,379 --> 00:27:20,862
These crinoids,
or sea lilies,
362
00:27:20,896 --> 00:27:23,620
look like plants,
but are, in fact, animals.
363
00:27:27,034 --> 00:27:29,517
Their long stalks
ensure that their umbrella,
364
00:27:29,551 --> 00:27:31,551
of feeding tentacles,
are positioned
365
00:27:31,586 --> 00:27:34,068
to best effect
in the current.
366
00:27:34,103 --> 00:27:36,241
Particles are swept
onto the arms,
367
00:27:36,275 --> 00:27:39,620
and carried down to a mouth
in the middle of the umbrella.
368
00:27:42,206 --> 00:27:46,103
These sudden movements
swat away tiny amphipods
369
00:27:46,137 --> 00:27:49,000
that try to steal
the sea lily's captures.
370
00:27:58,068 --> 00:28:00,413
Coral reefs are not
supposed to exist
371
00:28:00,448 --> 00:28:01,689
in total darkness,
372
00:28:01,724 --> 00:28:03,793
but recently,
a new kind of coral
373
00:28:03,827 --> 00:28:07,965
was found as deep
as 2,000 meters.
374
00:28:08,000 --> 00:28:10,551
In the cold waters
of a Norwegian fjord,
375
00:28:10,586 --> 00:28:13,206
there was a deep-sea reef
30 meters high
376
00:28:13,241 --> 00:28:17,034
and 200 meters long.
377
00:28:17,068 --> 00:28:19,689
This coral gets no energy
from the sun,
378
00:28:19,724 --> 00:28:22,620
so it has to be very efficient
in catching food.
379
00:28:22,655 --> 00:28:24,275
Its polyps
are far larger
380
00:28:24,310 --> 00:28:26,517
than those of
shallow-water corals.
381
00:28:33,310 --> 00:28:34,827
These are, in fact,
382
00:28:34,862 --> 00:28:38,931
the largest coral polyps
in the ocean.
383
00:28:38,965 --> 00:28:43,862
They belong to
the deep-sea mushroom coral.
384
00:28:43,896 --> 00:28:46,758
Their 3-centimeter-long
tentacles can catch
385
00:28:46,793 --> 00:28:49,793
far larger prey
than other corals can.
386
00:28:53,068 --> 00:28:56,172
This necessity to capture every
particle of food
387
00:28:56,206 --> 00:28:58,655
that comes within reach
in this near desert
388
00:28:58,689 --> 00:29:02,689
has radically changed
many animals.
389
00:29:02,724 --> 00:29:05,310
Most tunicates
are filter feeders,
390
00:29:05,344 --> 00:29:08,275
but this one, uniquely,
has become a predator,
391
00:29:08,310 --> 00:29:10,241
and its greatly
enlarged siphon
392
00:29:10,275 --> 00:29:12,655
has been converted
into a trap.
393
00:29:24,000 --> 00:29:27,758
Most sea cucumbers
stay firmly on the bottom,
394
00:29:27,793 --> 00:29:32,068
but not this extraordinary
deep-sea species.
395
00:29:36,172 --> 00:29:38,517
Its skirts of skin
allow it to swim
396
00:29:38,551 --> 00:29:41,275
hundreds of meters
above the sea floor.
397
00:29:56,172 --> 00:29:59,172
Eventually, it will descend,
and, with luck,
398
00:29:59,206 --> 00:30:01,241
will land on fresh
feeding grounds.
399
00:30:09,862 --> 00:30:12,758
This, though, has to be
the most extraordinary
400
00:30:12,793 --> 00:30:14,413
animal design
of all.
401
00:30:14,448 --> 00:30:17,310
It's a polychaete worm,
and normally, you would expect
402
00:30:17,344 --> 00:30:21,724
the long, pulsating body to be
stuck firmly in the sediment.
403
00:30:24,310 --> 00:30:28,793
This worm, alone in its group,
swims in the open water.
404
00:30:33,689 --> 00:30:36,034
Propelling itself
with its yellow frill,
405
00:30:36,068 --> 00:30:39,793
it moves about, and so finds
new sources of food,
406
00:30:39,827 --> 00:30:42,862
or maybe succeeds in escaping
from a predator.
407
00:30:48,103 --> 00:30:51,379
This is chimaera,
a close relative of the sharks,
408
00:30:51,413 --> 00:30:54,793
less than a meter long.
409
00:30:54,827 --> 00:30:58,724
Sensory pits on its chin help it
hunt prey on the bottom,
410
00:30:58,758 --> 00:31:01,275
while its surprisingly
large eyes may help it
411
00:31:01,310 --> 00:31:03,034
spot bioluminescence.
412
00:31:11,689 --> 00:31:13,965
Large fish
are rare down here.
413
00:31:14,000 --> 00:31:17,000
There's simply not enough
live prey to sustain them.
414
00:31:17,034 --> 00:31:19,448
Most have become
scavengers.
415
00:31:19,482 --> 00:31:24,620
A dead tuna has attracted
a deep-sea conger eel...
416
00:31:24,655 --> 00:31:27,655
and a sixgill shark.
417
00:31:27,689 --> 00:31:30,655
These monsters grow to
8 meters long.
418
00:31:44,862 --> 00:31:47,931
Sixgills are
living fossils.
419
00:31:47,965 --> 00:31:51,689
For 150 million years,
they have existed unchanged,
420
00:31:51,724 --> 00:31:55,724
living in water as deep
as 2,500 meters.
421
00:31:59,034 --> 00:32:01,344
Very few people
have ever been lucky enough
422
00:32:01,379 --> 00:32:03,827
to glimpse these sharks
from submersibles,
423
00:32:03,862 --> 00:32:06,827
and we know almost nothing
about their behavior.
424
00:32:14,724 --> 00:32:17,827
The body of a tuna
is a substantial meal,
425
00:32:17,862 --> 00:32:20,965
but just occasionally,
a really gigantic corpse
426
00:32:21,000 --> 00:32:23,482
drifts down
to the deep sea floor.
427
00:32:28,206 --> 00:32:32,793
This is the freshly dead carcass
of a 30-ton gray whale.
428
00:32:32,827 --> 00:32:36,793
It's resting on the sea floor
a mile down.
429
00:32:36,827 --> 00:32:39,206
It's only been on the bottom
for six weeks,
430
00:32:39,241 --> 00:32:42,344
but already, it has attracted
hundreds of hagfish.
431
00:32:44,862 --> 00:32:47,413
These ancient scavengers
are nearly always
432
00:32:47,448 --> 00:32:49,965
the first to discover
a fallen body,
433
00:32:50,000 --> 00:32:52,758
and are attracted
from miles around.
434
00:32:56,896 --> 00:32:59,793
They lack jaws,
and rasp at the flesh
435
00:32:59,827 --> 00:33:02,241
with two rows of horny teeth
on either side
436
00:33:02,275 --> 00:33:04,000
of their
sucker-like mouths.
437
00:33:09,206 --> 00:33:12,517
Next to arrive,
a sleeper shark,
438
00:33:12,551 --> 00:33:15,068
a real deep-sea
specialist.
439
00:33:15,103 --> 00:33:17,586
They grow to over
7 meters long,
440
00:33:17,620 --> 00:33:20,620
and have never been filmed
at such a depth before.
441
00:33:25,103 --> 00:33:28,655
The gaping wounds in the whale's
flank are its work.
442
00:33:36,000 --> 00:33:39,000
Unlike the hagfish,
it has powerful jaws,
443
00:33:39,034 --> 00:33:42,448
so it's able to rip off
huge chunks of meat.
444
00:33:49,137 --> 00:33:50,758
Sharks, hagfish,
445
00:33:50,793 --> 00:33:54,137
and a whole succession
of different deep-sea scavengers
446
00:33:54,172 --> 00:33:56,241
will feast on the carcass
for years
447
00:33:56,275 --> 00:33:58,827
before all its nutriment
has gone.
448
00:34:02,517 --> 00:34:05,413
18 months later,
when we returned to this whale,
449
00:34:05,448 --> 00:34:09,310
all that was left was a perfect
skeleton, stripped bare.
450
00:34:17,344 --> 00:34:19,724
It was almost as if
a museum specimen
451
00:34:19,758 --> 00:34:22,344
had been carefully laid out
on the sea floor.
452
00:34:27,172 --> 00:34:29,827
At first, the skeleton
seemed totally abandoned.
453
00:34:29,862 --> 00:34:31,310
But even after so long,
454
00:34:31,344 --> 00:34:33,862
there was still some flesh
left in the head.
455
00:34:40,758 --> 00:34:42,965
Hagfish have a skeleton
of cartilage,
456
00:34:43,000 --> 00:34:46,275
and are so flexible that they
can tie themselves into knots,
457
00:34:46,310 --> 00:34:49,551
and so get a better purchase
on the flesh they feed on.
458
00:34:56,137 --> 00:34:59,310
But smaller organisms
had fed here.
459
00:34:59,344 --> 00:35:02,655
A thick band of white bacteria
had formed on the mud
460
00:35:02,689 --> 00:35:06,413
outlining the original shape
of the whale.
461
00:35:06,448 --> 00:35:08,655
And on the skeleton itself,
462
00:35:08,689 --> 00:35:12,620
colonies of specialized bacteria
were extracting energy
463
00:35:12,655 --> 00:35:17,448
from the bones
themselves.
464
00:35:17,482 --> 00:35:20,206
Most remarkably,
and in huge abundance,
465
00:35:20,241 --> 00:35:24,103
polychaete worms were collecting
the last edible fragments.
466
00:35:24,137 --> 00:35:26,689
These are a new species that,
so far,
467
00:35:26,724 --> 00:35:31,827
have only been found on
the fallen bodies of whales.
468
00:35:31,862 --> 00:35:35,793
Scientists have discovered
178 different animals
469
00:35:35,827 --> 00:35:37,793
on a single
whale vertebra,
470
00:35:37,827 --> 00:35:41,172
most of which have been found
nowhere else.
471
00:35:41,206 --> 00:35:43,896
This whale,
lying over a mile down,
472
00:35:43,931 --> 00:35:46,172
was not filmed
from a submersible
473
00:35:46,206 --> 00:35:47,793
with an acrylic sphere.
474
00:35:47,827 --> 00:35:52,000
Such craft can't go
as deep as this.
475
00:35:52,034 --> 00:35:53,724
To withstand
the pressure here,
476
00:35:53,758 --> 00:35:56,758
you need a far stronger
submersible.
477
00:35:56,793 --> 00:35:59,862
This is Alvin,
a 2-meter-wide sphere
478
00:35:59,896 --> 00:36:01,413
with just enough
room in it
479
00:36:01,448 --> 00:36:04,137
for a pilot
and two observers.
480
00:36:04,172 --> 00:36:06,448
Its walls are made
of titanium.
481
00:36:06,482 --> 00:36:08,448
The viewing ports
have to be tiny.
482
00:36:08,482 --> 00:36:10,275
Any larger,
and the submersible
483
00:36:10,310 --> 00:36:15,689
would implode under
the enormous pressure down here.
484
00:36:15,724 --> 00:36:19,517
Alvin can dive
to 4,500 meters,
485
00:36:19,551 --> 00:36:22,068
3 miles below
the surface.
486
00:36:25,896 --> 00:36:28,827
Around 3,000 meters,
the continental slope
487
00:36:28,862 --> 00:36:33,379
finally flattens out,
and joins the abyssal plain.
488
00:36:33,413 --> 00:36:36,137
This covers over half
the Earth's surface.
489
00:36:36,172 --> 00:36:39,172
Mostly, it's completely flat,
but in places,
490
00:36:39,206 --> 00:36:43,413
it's gashed by massive trenches
hundreds of miles wide.
491
00:36:50,413 --> 00:36:53,172
The deepest of these
is the Mariana Trench,
492
00:36:53,206 --> 00:36:56,379
which drops to over 7 miles
below sea level.
493
00:37:03,827 --> 00:37:07,206
There are just five
manned submersibles worldwide
494
00:37:07,241 --> 00:37:09,344
that can reach
the abyssal plain,
495
00:37:09,379 --> 00:37:12,034
and between them, so far,
they have explored
496
00:37:12,068 --> 00:37:14,034
less than 1% of it.
497
00:37:16,137 --> 00:37:19,482
There are 1,000 times fewer
large animals down here
498
00:37:19,517 --> 00:37:21,551
than on
the continental slope,
499
00:37:21,586 --> 00:37:24,103
but in places,
hundreds of brittle stars
500
00:37:24,137 --> 00:37:26,931
march over the sea bed
in search of food.
501
00:37:29,862 --> 00:37:32,310
Fish have been found
right down to the bottom
502
00:37:32,344 --> 00:37:34,275
of the deepest trenches.
503
00:37:34,310 --> 00:37:38,586
Most come from one family,
the aptly named "rattails."
504
00:37:41,793 --> 00:37:43,620
They forage
near the sea floor,
505
00:37:43,655 --> 00:37:45,931
and use their battery
of sensory pits
506
00:37:45,965 --> 00:37:50,241
to follow odor trails
from rotting carcasses.
507
00:37:50,275 --> 00:37:52,655
Rattails can travel
long distances
508
00:37:52,689 --> 00:37:55,482
across the abyssal plain
in search of food,
509
00:37:55,517 --> 00:37:59,000
but others down here
prefer to sit and wait.
510
00:38:01,655 --> 00:38:03,827
This is a tripod fish.
511
00:38:03,862 --> 00:38:07,275
It supports itself on two
specially adapted fin rays,
512
00:38:07,310 --> 00:38:12,517
and can sit motionless
for hour after hour.
513
00:38:12,551 --> 00:38:16,586
It does have tiny eyes,
but it's almost totally blind.
514
00:38:16,620 --> 00:38:20,586
It locates potential prey with
a pair of fins behind its head,
515
00:38:20,620 --> 00:38:23,655
which are sensitive
to even tiny movements.
516
00:38:29,931 --> 00:38:32,758
We know more about
the surface of the moon
517
00:38:32,793 --> 00:38:35,482
than we do about
the abyssal plain.
518
00:38:35,517 --> 00:38:39,379
Every dive still produces
complete surprises.
519
00:38:45,034 --> 00:38:49,034
This deep-sea octopus is
about the size of a beach ball,
520
00:38:49,068 --> 00:38:51,655
and has been
nicknamed "Dumbo."
521
00:39:02,275 --> 00:39:04,965
An umbrella of skin
between its tentacles
522
00:39:05,000 --> 00:39:07,551
and its extraordinary
flapping ears
523
00:39:07,586 --> 00:39:10,206
allow Dumbo
to hover effortlessly
524
00:39:10,241 --> 00:39:13,448
over the sea floor
as it searches for food.
525
00:39:31,068 --> 00:39:33,862
Right in the middle
of the abyssal plain
526
00:39:33,896 --> 00:39:37,655
lie the largest geological
structures on our planet...
527
00:39:44,379 --> 00:39:46,275
...the mid-ocean ridges.
528
00:39:52,620 --> 00:39:55,413
Rising almost 2 miles
off the sea floor,
529
00:39:55,448 --> 00:39:59,137
the ridges extend
for over 28,000 miles,
530
00:39:59,172 --> 00:40:02,068
the largest mountain chain
on Earth.
531
00:40:07,827 --> 00:40:10,275
When submersibles
finally succeeded
532
00:40:10,310 --> 00:40:12,827
in reaching the ridges
in the 1970s,
533
00:40:12,862 --> 00:40:16,344
they found an extraordinary
world with mile upon mile
534
00:40:16,379 --> 00:40:18,758
of once-molten rock
that had welled up
535
00:40:18,793 --> 00:40:21,758
from the deep in the past,
and had now solidified.
536
00:40:26,620 --> 00:40:28,758
They discovered
towering chimneys
537
00:40:28,793 --> 00:40:32,103
pouring out water
as hot as molten lead.
538
00:40:59,620 --> 00:41:03,689
At the surface, water becomes
steam at 100 degrees centigrade,
539
00:41:03,724 --> 00:41:06,758
but down here, under the immense
pressure of the ocean,
540
00:41:06,793 --> 00:41:08,482
it remains liquid
at temperatures
541
00:41:08,517 --> 00:41:11,137
as hot as
400 degrees centigrade.
542
00:41:16,862 --> 00:41:19,724
The submersible
has to move carefully.
543
00:41:19,758 --> 00:41:22,551
Disaster is very close
when surrounded by
544
00:41:22,586 --> 00:41:26,655
such enormous temperatures
and pressures.
545
00:41:26,689 --> 00:41:28,724
And here,
where the very water
546
00:41:28,758 --> 00:41:30,586
is loaded with
hydrogen sulfides
547
00:41:30,620 --> 00:41:32,758
poisonous to normal
life processes,
548
00:41:32,793 --> 00:41:34,689
they found
living creatures.
549
00:41:39,586 --> 00:41:43,793
Some of the chimneys were
encrusted with white tubes.
550
00:41:43,827 --> 00:41:45,241
The tubes were inhabited
551
00:41:45,275 --> 00:41:47,793
by a new species
of polychaete worm
552
00:41:47,827 --> 00:41:49,517
that was exposed
to temperatures
553
00:41:49,551 --> 00:41:51,758
as high as
80 degrees centigrade.
554
00:41:54,275 --> 00:41:56,793
No other animal on Earth
was known to tolerate
555
00:41:56,827 --> 00:41:59,655
such high temperatures,
so the scientists called
556
00:41:59,689 --> 00:42:04,551
these creatures
"Pompeii worms."
557
00:42:04,586 --> 00:42:07,068
But this was just
the beginning.
558
00:42:07,103 --> 00:42:09,379
Nearby, there were chimneys
completely covered
559
00:42:09,413 --> 00:42:13,379
by whole communities
of different organisms.
560
00:42:13,413 --> 00:42:16,965
The bottom of the vent was
encrusted with large mussels.
561
00:42:20,172 --> 00:42:22,275
There were swarms
of white crabs,
562
00:42:22,310 --> 00:42:25,448
and most spectacular of all,
dominating the chimney
563
00:42:25,482 --> 00:42:27,758
were hundreds of
bright-red tube worms,
564
00:42:27,793 --> 00:42:31,034
each 2 meters long
and 4 centimeters wide.
565
00:42:33,551 --> 00:42:35,379
Until these creatures
were discovered,
566
00:42:35,413 --> 00:42:39,034
all life on Earth was thought
to be dependent on the sun.
567
00:42:39,068 --> 00:42:41,931
But here, in the complete
darkness of the deep,
568
00:42:41,965 --> 00:42:44,586
they had discovered
a rich density of life
569
00:42:44,620 --> 00:42:47,965
that clearly derived no energy
from the sun.
570
00:42:54,896 --> 00:42:57,000
So, what do they live on?
571
00:42:57,034 --> 00:43:00,413
The answer was found within
the tube worms themselves.
572
00:43:00,448 --> 00:43:03,448
They were packed full
of specialized bacteria
573
00:43:03,482 --> 00:43:06,517
that are able to derive energy
from the sulfides
574
00:43:06,551 --> 00:43:08,413
that are pouring
from the vents.
575
00:43:13,137 --> 00:43:15,206
The worms' plumes
were bright red
576
00:43:15,241 --> 00:43:17,758
with hemoglobin that carries
sulfides and oxygen
577
00:43:17,793 --> 00:43:21,034
down to the bacteria.
578
00:43:21,068 --> 00:43:24,620
These bacterial colonies are
the primary source of energy
579
00:43:24,655 --> 00:43:26,620
for all the life
that lives here.
580
00:43:26,655 --> 00:43:28,724
The mussels were
packed with them.
581
00:43:28,758 --> 00:43:31,931
Just as green plants are
the basis of life for animals
582
00:43:31,965 --> 00:43:33,206
living in the sun,
583
00:43:33,241 --> 00:43:36,137
so these bacteria
and other microbes are
584
00:43:36,172 --> 00:43:40,379
at the foot of the food chain on
which over 500 species depend.
585
00:43:46,827 --> 00:43:49,655
Crabs and shrimps
feed off bacteria,
586
00:43:49,689 --> 00:43:53,413
and even try to steal pieces
of tube worm plumes.
587
00:43:59,206 --> 00:44:03,724
Since the vents were first
visited by biologists in 1979,
588
00:44:03,758 --> 00:44:09,517
a new species has been described
every 10 days.
589
00:44:09,551 --> 00:44:11,241
At the top
of the food chain,
590
00:44:11,275 --> 00:44:14,482
fish that never stray far
from the vents.
591
00:44:14,517 --> 00:44:16,172
But they,
or their descendants,
592
00:44:16,206 --> 00:44:18,620
will have to move eventually,
for we now know
593
00:44:18,655 --> 00:44:20,689
that individual vents
are rarely active
594
00:44:20,724 --> 00:44:22,655
for more than
a few decades.
595
00:44:37,655 --> 00:44:41,827
Such a density of life
living in such harsh conditions
596
00:44:41,862 --> 00:44:44,517
in the middle of a vast
and otherwise barren
597
00:44:44,551 --> 00:44:47,448
abyssal plain
astounded the biologists
598
00:44:47,482 --> 00:44:49,000
who first saw it.
599
00:44:52,379 --> 00:44:55,137
It seemed to them that
here was evidence of how
600
00:44:55,172 --> 00:44:56,413
life on this planet,
601
00:44:56,448 --> 00:44:58,448
which certainly started
in the sea,
602
00:44:58,482 --> 00:44:59,827
might have begun.
603
00:45:05,241 --> 00:45:08,310
Deep-sea submersibles
made an even more
604
00:45:08,344 --> 00:45:11,482
extraordinary discovery
in 1990.
605
00:45:21,931 --> 00:45:23,827
Over half a mile down,
606
00:45:23,862 --> 00:45:26,137
at the bottom of
the Gulf of Mexico,
607
00:45:26,172 --> 00:45:29,724
they came across what appeared
to be an underwater lake
608
00:45:29,758 --> 00:45:35,310
over 20 meters long,
with its own sandy shore.
609
00:45:35,344 --> 00:45:38,965
Around its edge, there even
seemed to be a tide line.
610
00:45:39,000 --> 00:45:41,000
But this couldn't be,
of course.
611
00:45:41,034 --> 00:45:44,172
This was underwater.
612
00:45:44,206 --> 00:45:47,655
In fact, the lapping edge
was created by a thick soup
613
00:45:47,689 --> 00:45:51,793
of salty brine far heavier
than the surrounding seawater.
614
00:45:51,827 --> 00:45:53,379
And the sand
was made up of
615
00:45:53,413 --> 00:45:57,448
hundreds of thousands
of mussels.
616
00:45:57,482 --> 00:46:01,068
Once again, in the midst of
a totally barren seabed,
617
00:46:01,103 --> 00:46:03,896
an extraordinarily rich
oasis of life
618
00:46:03,931 --> 00:46:06,862
totally independent
of the sun's energy.
619
00:46:10,827 --> 00:46:13,931
The source of energy this time
was not sulfides,
620
00:46:13,965 --> 00:46:17,275
but methane bubbling out of
the sea bed.
621
00:46:17,310 --> 00:46:20,620
And once again, the mussels
carried special bacteria
622
00:46:20,655 --> 00:46:24,103
capable of fixing
the methane's energy.
623
00:46:24,137 --> 00:46:27,413
Just like the hot vents,
a complete ecosystem
624
00:46:27,448 --> 00:46:30,034
had developed
based on the bacteria.
625
00:46:30,068 --> 00:46:34,000
There was an enormous variety
of completely new species--
626
00:46:34,034 --> 00:46:37,482
shrimps,
weird squat lobsters,
627
00:46:37,517 --> 00:46:40,551
and bright-red
polychaete worms.
628
00:46:49,310 --> 00:46:52,241
These oases were called
"cold seeps,"
629
00:46:52,275 --> 00:46:55,206
and were surprisingly similar
to the hot vents.
630
00:47:00,793 --> 00:47:03,344
The geological processes
in the sea floor
631
00:47:03,379 --> 00:47:05,758
that produce methane
also tend to result in
632
00:47:05,793 --> 00:47:08,034
the release of
hydrogen sulfides.
633
00:47:08,068 --> 00:47:10,103
It was hardly surprising,
then, when,
634
00:47:10,137 --> 00:47:11,689
not far from
the brine pool,
635
00:47:11,724 --> 00:47:14,034
they found tube worms.
636
00:47:16,103 --> 00:47:18,931
Extensive fields
of tube worms
637
00:47:18,965 --> 00:47:21,793
that stretch for
hundreds of meters.
638
00:47:21,827 --> 00:47:24,655
This new species
also uses bacteria
639
00:47:24,689 --> 00:47:26,586
to fix energy
from sulfides,
640
00:47:26,620 --> 00:47:30,827
but it extracts them
directly from the ground.
641
00:47:33,724 --> 00:47:36,517
Their beautiful gills
are only used
642
00:47:36,551 --> 00:47:38,931
to supply oxygen
to the bacteria.
643
00:47:41,551 --> 00:47:46,655
Amazingly, these tube worms
are over 200 years old.
644
00:47:46,689 --> 00:47:49,172
While hot-vent tube worms
are thought to be
645
00:47:49,206 --> 00:47:51,655
the fastest-growing
invertebrates in the sea,
646
00:47:51,689 --> 00:47:54,379
these appear
to be far slower.
647
00:47:54,413 --> 00:47:56,517
All the more reason
to protect your gills
648
00:47:56,551 --> 00:47:58,241
from biting amphipods.
649
00:48:02,758 --> 00:48:05,896
The energy sources exploited
by the hot-vent animals
650
00:48:05,931 --> 00:48:08,448
may suddenly fail,
but here,
651
00:48:08,482 --> 00:48:12,310
life can enjoy a more stable
geological future.
652
00:48:16,344 --> 00:48:20,206
To discover, within 10 years,
two completely new ecosystems,
653
00:48:20,241 --> 00:48:22,689
both totally independent
of the sun's energy,
654
00:48:22,724 --> 00:48:25,068
has been quite
extraordinary.
655
00:48:25,103 --> 00:48:28,034
So far, we have
explored just 1%
656
00:48:28,068 --> 00:48:29,793
of the deep
ocean floor.
657
00:48:29,827 --> 00:48:33,275
Who knows what is still
out there to be discovered?