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It's easy to forget how vast and deep
the ocean really is.
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About 60% of it is actually
a cold and dark region
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known as the deep ocean.
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And it reaches down to 11,000 meters.
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Yet, this remote zone is also one
of the greatest habitats on Earth,
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harboring a huge diversity of life,
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from giant squids and goblin sharks
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to minuscule animals
smaller than a millimeter.
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How do so many species thrive
in this underwater world?
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Over the decades, intrepid scientists
have ventured there to find out.
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Traveling down through the water column,
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pressure increases
and light begins to wane.
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At 200 meters, photosynthesis stops
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and temperature decreases
from surface temperatures
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by up to 20 degrees Celsius.
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By 1000 meters, normal sunlight
has disappeared altogether.
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Without light, life as we know it
seems impossible.
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That's why in 1844, the naturalist
Edward Forbes
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wrote his Azoic Theory,
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Azoic, meaning without animals.
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Forbes was sure that nothing could survive
below 600 meters
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on account of the lack of light.
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Of course, the discovery
of deep-sea species proved him wrong.
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What Forbes failed to take into account
is something called marine snow,
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which sounds much nicer than it is.
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Marine snow is basically organic matter,
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things like particles of dead algae,
plants, and animals,
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drifting down into the depths
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and acting as food for deep-sea animals.
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Largely thanks to that,
abundant life forms exist in the darkness,
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adapting to a harsh reality where only
the weird and wonderful can survive.
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Fish with cavernous mouths,
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spiky teeth jutting from their jaws,
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and lamp-like structures
protruding from their heads,
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like the anglerfish which entices prey
with its misleading glow.
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Several sea creatures have perfected
this lightning technique
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known as bioluminescence,
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using it to lure prey,
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distract predators,
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or attract mates.
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Some creatures use it for camoflauge.
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In parts of the water column where
only faint blue light filters through,
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animals bioluminesce to match the glow.
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Predators or prey looking up
from below
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are deceived by this camoflauge,
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unable to see the creatures silhouette.
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Such otherworldly adaptations also arise
from the need to locate
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and snatch up food before it drifts away.
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Some sea animals, like jellyfish,
comb jellies and salps
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can migrate between depths
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partially because
their 90% water consistency
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allows them to withstand immense pressure.
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But they're the exception.
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Most deep-sea creatures are confined
to a narrow range in the water column
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where nutrients are scarce
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since the food drifting downwards
from the surface
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rapidly sinks to the sea floor.
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Plunging all the way down,
we find more exotic creatures.
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Some take on dwarfism,
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a trait that transforms them
into miniature versions of animals
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we see closer to the surface.
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It's thought that reduced
food availability causes the shrinkage.
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Only a tiny fraction of the food produced
at the surface reaches the sea floor,
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so being small gives animals
a low energy requirement
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and an adaptive advantage.
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And yet, the sea is also the land
of giants.
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Here, gargantuan squids can reach
18 meters long.
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Isopods scuttle around the sea floor
like enormous wood lice.
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There are long-limbed
Japanese spider crabs,
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and oarfish, whose bodies stretch
to 15 meters.
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This trait is known as gigantism,
and it's something of a mystery.
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It's thought that high oxygen levels
may drive extreme growth in some species,
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while the colder temperatures promote
longer life spans,
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giving animals the opportunity
to grow massive.
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Many of these exotic sea beasts will never
experience sunlight.
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Some will venture up through
the water column to feed,
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and a few will actually break the waves,
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reminding us at the surface
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about the incredible survival skills
of the ocean's deepest inhabitants.
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Humans still have an astounding
95% of the ocean left to explore.
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So those depths remain a great mystery.
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What other untold wonders lie far below,
and which ones will we discover next?