So deep that if you dropped Mount Everest inside,

its peak would still be more than

a kilometer underwater.

So deep that no light reaches the bottom.

And if you could feel it, the pressure would be

about equal to the weight of

48 jumbo jets.

Yet, somehow, life finds a way.

Very weird life.

The truth is, at first glance...

Douglas Bartlett: You wouldn't be very impressed.

It's gonna be this

kind of silky, gray-green sediment.

Narrator: But if you put out some food,

some of the planet's strangest creatures

would emerge from the darkness.

Like these.

They're crustaceans called amphipods.

And some individuals can grow

up to 30 centimeters long,

or about the size of an American football.

Now, like lobsters,

these animals have hard exoskeletons

made of calcium carbonate,

which you normally wouldn't find down here,

more than 10,000 meters down.

Because once you pass 4,500 meters or so,

the pressure is so great

and the temperature is so low

that calcium carbonate dissolves.

But these amphipods have a secret weapon.

Or rather, shield.

The crustaceans are covered

with an armor made of aluminum,

which they synthesize in their bodies,

using aluminum found in the seafloor.

It's a good thing, too,

because those shells are their best defense

against something else lurking in the abyss.

The Mariana snailfish,

aka the deepest fish ever discovered,

which scientists have seen

more than 8,000 meters down.

And there are a lot

of strange things about these fish.

They have flexible bones,

which scientists think helps them withstand pressure.

They're blind, because, well, when it's that dark,

there's no point in seeing.

And...

Bartlett: Their skin is translucent,

so you can see their internal organs.

Narrator: But they're also one of the trench's

top predators.

And if you want proof,

check out this terrifying X-ray image.

Now, snailfish are certainly odd.

But then again, you haven't yet met...

Bartlett: A xenophyophore.

Narrator: It's a single-celled organism

akin to a giant amoeba.

In fact, at about 10 centimeters long,

it's one of the largest

single-celled organisms on Earth.

The trench also has what Bartlett calls...

Bartlett: These little sea pigs.

Narrator: They're small, transparent sea cucumbers

that crawl along the ocean floor

on tentacle-like legs.

But perhaps the most surprising thing you'll discover

inside the Mariana Trench is this:

Plastic.

In 1998, a remotely operated submersible

detected a plastic bag

at 10,898 meters.

And in 2019, an explorer reported

signs of plastic debris even further down.

What's more, researchers have found microplastics

inside the stomachs of amphipods

in the Challenger Deep.

They called it "the deepest record

of microplastic ingestion."

And all that goes to show that even here,

in the most remote place on the planet,

where only four people have ever visited,

there are signs of our vast impact on the world.