Deep below the warm tropical waters of
the Pacific Ocean,
there is a dark and almost frozen world.
A place so dangerous to explore that we
know precious little about it.
Finding anything alive there was once
believed to be impossible. Conditions
are so extreme that even the cells that
make up all living things
would be destroyed.
Bones and shells would simply dissolve.
The processes essential to life would
come to a standstill.
That was until 1960 when a creature was
witnessed at the very bottom.
The first signs of life had been found.
But things got even more strange because
not only was life found at these depths,
that life had adapted to here and
nowhere else on Earth.
Much of what we know about this
secretive place comes from rare
specimens that have been bought up by
remote probes or are occasionally caught
by deep sea fishing.
strange creatures that have adapted to
living in conditions that we still don't
fully understand
and are sometimes washed up on our
shores.
Removed from their natural environment,
they are distorted out of shape, often
destroyed altogether, so we can only
guess what they should look like and how
they might live.
The vast expanse of our deep ocean
floors is the last unexplored frontier
on our planet, waiting to be discovered.
I'm James Stewart and you're watching
Astramm Earth.
Join me in this video as we take a
journey into the deepest of them all,
the Mariana Trench.
Our
journey begins 150 years ago when the
British ship HMS Challenger was nearing
the end of a 4-year mission.
The first ever mapping of the ocean
floors. They had already taken hundreds
of soundings, a backbreaking job in all
weathers, from blistering tropical heat
to frozen polar waters.
lowering a lead weight until it touched
the ocean floor, then pulling up meter
after meter of cold and heavy wet rope.
The picture that emerged was of a
featureless surface of mud and silt
around 3 to 4 km below the surface.
alone in the empty ocean 2,000 km east
of the Philippines. They were taking
another routine sounding. On this day,
however, the lead weight did not touch
the bottom at 3 km down, nor at four or
even five. It kept lowering into the
deep. More rope was added, and still it
went down. We can only guess how they
must have felt as they tied on yet more
rope. And that lead weight kept sinking
into the depths right underneath the
thin wooden hull of their ship.
Sailing the high seas in those times was
a treacherous ordeal.
The crews trusted their faith in
traditions and superstitions.
Legends told of enormous creatures that
rose from the depths, gripping entire
ships in their writhing tentacles and
pulling them under.
This sounds far-fetched to us today, but
in those days, such fears were very
real. Eventually, the weight hit the
bottom more than 8 km down.
What they had found is now known as the
Mariana Trench. And if they had been
just a little further to the west, they
would have found the deepest hole in the
surface of our planet, the Challenger
Deep, 11 km down. Mount Everest would
disappear into this hole and it would
keep sinking down 2 kilometers below the
surface.
The Mariana Trench is vast, a 2,000
km long curved valley on the ocean
floor, almost 70 km wide. It begins
2,000 km south of Japan, first curving
southeast, then turning westwards
towards the Philippines.
The valley size to the west are steep
cliffs of exposed ignous rock.
To the east, it rises more gently,
opening onto an empty ocean floor for
12,000 almost featless kilome until
reaching Mexico.
The scale is hard for us to imagine.
Just the Challenger Deep alone, which is
only a tiny part of the whole trench,
could swallow up five Grand Canyons.
you want your digital life a bit more private.
The Mariana Trench is part of an almost
continuous series of unstable and
constantly moving chasms in the Earth's
crust that encircle the Pacific Ocean.
They are matched by a ring of volcanoes
known as the ring of fire. An
astonishing 90% of all earthquakes are
caused by movements of this 40,000 km
fracture where rock faces many kilome
deep into the earth grind together and
destroy each other.
We are only now beginning to learn how
the surface of our planet has changed
over time. why the continents are
arranged the way they are and how these
deep rifts in the planet's surface play
a vital role in that story.
To understand what created this
remarkable geological feature, it helps
look first at the Atlantic Ocean on the
other side of the Americas.
The surface of our planet is made from
continents and oceans. That is not as
simple as which parts are above water
and which are hidden below the waves.
The continents and the oceans are
completely different components of the
Earth's crust. All floating on a ball of
hot rock called magma.
Think of the continents as icebergs
floating on an ocean of magma.
enormous lumps of the Earth's crust, a
drift in the oceans, and like icebergs,
mostly hidden below the surface.
Between them is a thin layer of ocean
crust filling the gaps, similar in scale
to the skin of an apple. The continents
are ancient. They are thick layers of
varying rock types that have built up
over billions of years.
Ocean crust is much younger, mere
millions of years old and thinner, made
from solidified magma.
The ocean floors and the continents move
around, dragged across the globe by
thermal currents in the magma below.
All of those continents were once
crammed together in one superc continent
that we call pangia. For around 200
million years, they have been moving
apart. The Atlantic Ocean is getting
bigger as the Americas move away from
Africa and Europe. As they move apart, a
new ocean floor is being continuously
made and what is called a divergent
fault, filling the gap roughly down the
center of the ocean.
This process is driven by the thermal
currents in the underlying magma.
They rise up, then spread east and west,
forcing the continents apart and
creating more ocean floor.
If the Americas are moving westwards
away from Africa and Europe, then they
must be getting closer to Asia and
Australia, making the Pacific Ocean
smaller. The forces that create new
ocean floor in the Atlantic are also at
work in the Pacific, driven by the
thermal currents in the magma
underneath.
This is constantly producing a new ocean
floor called the Pacific tectonic plate
which flows outwards like a geological
conveyor belt. But the Pacific Ocean is
getting smaller. So where does all this
ocean floor go?
All around the outer limits of the
Pacific Ocean, this outwardly flowing
ocean crust meets the continents of the
Americas to the east and Asia and
Australia to the west. As it moves
outwards, the ocean floor must go
somewhere. It's forced downwards,
sinking under the continents around it,
returning to the magma from which it
formed, a process called subduction.
This is the biggest recycling operation
on the planet.
[Music]
This massive line of destruction is what
creates earthquakes and the volcanoes
that surround the Pacific Ocean, the
ring of fire. As the ocean floor is
forced down into the magma below, some
of it melts and rises, bursting out at
the surface as volcanoes.
That is why on the outer side of these
subduction faults, you find a line of
volcanoes. And at the faults themselves,
you find the deep ocean trenches.
As the Pacific floor moves westwards
towards our trench, it cools and gets
denser. That causes it to sink lower
towards the center of the Earth as
gravity pulls it down.
Consequently, the ocean here gets deeper
and deeper. The Pacific plate that flows
into our trench is 170 million years
old, the oldest ocean crust on the
planet. It was formed when the
continents first started to break apart,
and it's now come to the end of its
life.
At the western edge of the Pacific
Ocean, it meets the Philippines plate.
This younger and less dense slab of the
Earth's crust sits much higher above the
mantle. It simply rides over the older
sinking ocean floor, pushing it further
down, bending a layer of solid rock
that's several kilometers thick.
The forces involved are unimaginable.
It is this junction of the towering
upper tectonic plate and the sinking
Pacific plate that creates the Mariana
Trench.
This zone of destruction creates some of
the geological wonders of the world.
Here there are gigantic active mud
volcanoes pouring out hydrogen into the
Pacific waters. One of which is 50 km in
diameter. There is a volcano that spews
out almost pure carbon dioxide which
emerges as a liquid, not a gas because
of the enormous pressure at these
depths. Another has a pool of molten
sulfur in its crater found only here and
on one of the moons of Jupiter. Deep
fishes vent columns of boiling water
rich in minerals believed to contain the
secrets of the origins of life on our
planet.
Our interest today is not amongst these
volcanoes and thermal vents. We want to
see what it would be like to travel down
into the trench itself, thousands of
meters deeper into the ocean, and then
make the most extreme dive of them all
into the Challenger Deep.
You may think that at 10,935
m, the Mariana Trench is somehow a freak
of geology, an unexpected deep hole of
unusual depth.
But other trenches around the Pacific
are of a similar depth. The nearby Tonga
Trench is 10,800 m deep and the
Philippine trench 10,540.
These rifts in the Earth's crust are
constantly changing and the depression
that causes the Challenger deep is only
temporary.
It will one day be dragged down into the
magma and somewhere else will become the
deepest hole in the planet.
There are a lot of problems to overcome
to explore such depths underwater, but
the biggest is pressure.
If you swim to the bottom of a pool, you
can feel the water pressure in your
ears. Even at just three or four meters,
it gets quite uncomfortable. Well, at
this sort of depth, the pressure is
unimaginable. It's more than a thousand
times the pressure at the surface,
equivalent to a ton weight on your
thumbnail. And just the same as a ton
weight on your thumbnail, that pressure
is enough to destroy most living cells.
But it isn't just living things that get
crushed into oblivion. The destructive
power of this force is astonishing. Even
equipment designed to cope with these
extreme depths can fail in spectacular
fashion. In 2014, an unmanned deep sea
exploration vehicle called Nerius
suffered a catastrophic implosion during
a dive into the Kerdc Trench to the
north of New Zealand, completely
destroying it.
The military submarines that secretly
prowl our oceans can only dive safely to
a depth of around 1,500 m. To get to the
bottom of the Mariana Trench, you need a
serious piece of kit.
Amazingly, two people managed this crazy
descent as far back as 1960.
Don Walsh of the US Navy and Jacques
Picard, a Swiss oceanographer, made the
perilous dive into the Trieste, a tiny
bath scape, an incredibly strong
pressure vessel resembling a spherical
bomb slung beneath a buoyancy tank. At a
depth of around 9 km, there was an
almighty bang, but that didn't deter our
intrepid explorers. They had a quick
look around, couldn't see anything to
miss, so they continued the dive. What
they didn't notice was that one of the
thick outer plexiglass window blocks had
cracked. One of the key components that
prevented their tiny capsule from
imploding. They were at the very limit
of what this submersible was capable of.
But still they went deeper, 3 km deeper.
It took them nearly 5 hours to reach the
bottom. Their view when they got there
was limited to two tiny viewing ports
just 50 mm in diameter and a small area
in the pitch black that was illuminated
by their lights.
Their arrival had stirred up the
sediment on the sea floor. So for a
while they could see nothing at all. But
amazingly they did see life. They saw
what they believed to be a flat fish
moving along the top of the sediment.
But it's now believed that this was
probably a sea cucumber, one of the few
species known to exist at this depth.
They stayed for a mere 20 minutes before
having to make the ascent, which took
more than 3 hours. What they achieved
was so dangerous that nobody else would
make the same descent for another half a
century. During that time, only a few
unmanned vehicles were lowered into the
abyss. Yet nearly 7,000 people climbed
to the top of Mount Everest and 12
people went to the moon. That gives you
an idea of just how technically
challenging it is to explore these
depths. The next man's descent was not
until 2012 when James Cameron made the
first solo dive into the Challenger Deep
in the appropriately named Deep Sea
Challenger.
Since then, there have been a further 20
dives into the Challenger Deep, and the
number of people to make the short
journey has finally exceeded the number
of people that have traveled to the
moon.
In 2021, Hamish Harding made the longest
and deepest dive into the Challenger
Deep. 2 years later, he was sadly among
five people killed when the Titan
submarine imploded on a mission to
explore the wreck of the Titanic at a
depth of only 3,800 m. The dangers of
deep sea dives should never be
underestimated.
Above the surface, there is nothing to
see but empty, featureless ocean. There
is no land for more than 300 km in any
direction. Descending into the water,
the first thing you notice is quiet and
calm. Just a few meters down, you are
below the buffeting of the waves.
Sunlight floods into the water from the
tropical sun and the importance of this
to all life on our planet is enormous.
We are in the epipalagic zone, also
known as the euphotic zone, the surface
layer that forms only 2 or 3% of the
oceans, but which supports life
everywhere above and below the water.
Here there is enough light to power
photosynthesis.
The process that splits carbon dioxide
into carbon used to build all life forms
on our planet and oxygen.
The phytolanton here produce half the
oxygen that we breathe. This is where
the ocean food chain starts. The
phytolanton which includes such things
as datoms and photosynthetic bacteria
are eaten by zup plankton tiny organisms
that float suspended in the warm surface
waters.
These are in turn eaten by larger
animals such as fish, jellyfish, even
whales.
Bigger fish eat the smaller fish. Sharks
eat the bigger fish. the whole food
chain gets going
and it all starts right here in the
epipagic zone. This is where you find
our food fish such as tuna, herring, and
cod.
Water absorbs light and as we go deeper,
the water soon becomes darker and more
blue. Here in the clear waters of the
Pacific with strong sunlight overhead,
the epipagic zone descends to about 200
m. Then we enter the twilight zone, also
called the misopalagic or the dysphotic
zone.
There is light here, but not enough to
power photosynthesis. Already the water
is much colder.
And as the light fades, we see the first
flashes of bioluminescence,
light produced by marine life in the
darker environments.
This part of the ocean teams with life.
The biomass of the fish in the Twilight
Zone is believed to be as much as the
rest of the ocean combined, possibly
more.
But as we go deeper, you'll get used to
me saying probably or possibly or
believed to be simply because we know so
little about our oceans and what is
found in them. The most abundant
vertebrate on the planet lives in these
waters between the light and the dark.
The bristle moth, a small fish with
spiny teeth.
They're only around 7 or 8 cm long, but
what they lack in size, they make up for
in numbers.
There are possibly quadrillions of them,
feeding mainly on the zoo plankton, an
indicator of just how much life is
supported by the thin layer of sunlit
waters at the surface.
As we descend deeper, the last faint
blue light from the surface disappears,
and the water becomes completely dark.
Well, maybe not completely because down
at these depths, bioluminescence really
comes into its own. This eerie and alien
looking light, mainly blue because this
is the color that travels furthest
through water, is used by some species
to find a mate and by others to hunt and
kill.
We are 1 kilometer down in the perpetual
darkness of the baopalagic zone or as I
prefer to call it the midnight zone
covering more than half the planet's
surface. Yet we still understand very
little about it. The temperature is a
steady 4° C and the pressure from the
weight of the water above us is already
becoming dangerous.
We are a long way below the maximum
depth for any sort of diving, even in a
pressure suit. And we're approaching the
limit that nuclear submarines can dive
to. As a species used to life at the
surface, that gives us a very negative
view of what life must be like here. But
it's important to remember that for
everything that lives in these depths,
this is normal. They are adapted to live
in these cold, dark waters and this
great pressure. Our camera lights pick
out almost a snowstorm of microorganisms
and floating food particles.
There is a lot going on here at the
upper levels. Anyway,
as we go even deeper, strange looking
creatures begin to appear. Some have
enormous eyes to enable them to see,
although what they can see in what to us
looks like total darkness, we can only
imagine. The owl fish uses the faintest
light to prey on shrimps and jellies.
Barrel eyes are small fish that use
their strange upward pointing eyes to
hunt from below their prey, able to live
and therefore presumably see in the
pitch dark as far down as 2,500
m.
Some go to the other extreme and have
almost given up on using sight, like the
small eye snipe eel. Unless you're using
enormous eyes to hunt or to find a mate,
there isn't much point in having them at
all down here. Instead of sight, most
species that live in this eerily dark
world use a series of pressure sensors
that detect anything that moves,
even if they are completely blind. This
enables them to hunt and kill. There are
many examples of animals that use light
to attract their prey. The best known is
the angler fish, which dangles a small
glowing lure. Anything that comes along
with ideas about eating this small
glowing morsel will itself be eaten. As
the angler fish closes its enormous
spinefilled jaws on its prey.
The largest eyes of any animal on Earth
are those of the giant squid.
Only a few of these monsters of the deep
have ever been seen. the largest to
date, measuring 13 m long. But there is
no reason to assume that they don't get
bigger than this, perhaps much bigger.
There is a tendency for species to grow
larger in deeper water, a phenomenon
called deep sea gigantism. And there are
a number of reasons for this. The bigger
you are, the less likely you are to
become a snack for something else. And
you can eat bigger prey yourself. As
food becomes more scarce the deeper we
go, it makes sense to be able to eat
anything that comes along, no matter
what size it is.
Being larger suits an existence where
meals become scarce, which may sound
illogical, but the bigger you are, the
longer you can go without eating. You
just have to hope that when lunch does
finally arrive, it's worth the wait.
Animals also live longer and therefore
grow larger simply because the chance of
meeting something that might eat them
become smaller.
The chimera, also known as the ghost
shark, has deadl looking eyes, fins like
wings, and like so many species at these
depths, an abnormally large head. Unlike
other sharks, they have permanent teeth
capable of crushing even the toughest
crustations they may find. Able to eat
anything big or small. The pelican eel
is a truly bizarre creature of the deep
with massive jaws and an extending
stomach capable of swallowing prey
larger than itself, which is a good
strategy to have if you're faced with
something that might be wanting to eat
you. That strategy isn't always
successful, however, and the pelican eel
is itself prayed upon by the lancet
fish, a predatory hunter of the deep
that grows up to 2 m in length.
We have now passed beyond the bottom of
the midnight zone, and we've entered the
deepest of the ocean's waters, the Hadel
zone. It is named after Hades, the Greek
god of the underworld. As well as being
dark and under immense pressure, the
temperature here is always close to
freezing. Currents of cold water flow
across the bottoms of the ocean through
these deep trenches from Antarctica.
Part of a global system of water
currents that is crucial for our varied
weather and climates across the planet.
To life forms that have adapted to these
depths, this constant supply of cold,
pressurized water is vital, enabling
them to access more oxygen in an
environment where every small benefit
makes the difference between life and
death.
Even the shallow parts of the Mariana
Trench are 8 km deep. The seafloor here
is covered in fine silt, distributed
easily by water currents, churned over
by the detritus eaters in their constant
search for food. It settles to a smooth
surface wherever we look.
There is more life here than in the open
water, and the lights of our
submersibles pick out sprawling mats of
microbial ooze on any rock formations
that rise above the covering of silt.
These are microorganisms that use
dissolved hydrogen sulfide from the
volcanic activity around the fault zone
to power a process known as
chemosynthesis.
This makes use of energy from chemical
reactions to support life instead of the
energy of the sun which powers
photosynthesis far above in the world of
light. It isn't anywhere near as
effective as photosynthesis. But in
these dark waters, you have to make the
most of anything that is available. It's
a rule of nature and where there is
potential it will be exploited. Just as
these microbes make life from the rocks
in this dark and barren place, they
themselves become a food source. And so
the cycle of life begins even at these
depths. The only other food supply is
whatever scarce organic matter floats
down from above. But after falling
through 8 km of water to get here,
passing the marine life that constantly
scavenges for any food that can be
found, very little makes it this far.
The main scavengers at this depth are
giant amphipods. Don't get too excited
by that word giant, but growing to more
than 30 cm, they are giants compared to
other amphipods, normally only a few
millimeters in length.
Translucent sea pigs, a type of sea
cucumber with long antenna-like
projections that seem to have many
functions, including acting as legs,
scavenge the sea floor, looking for
anything that may be nutritious. They
are attracted to carcasses that fall
into these depths and will appear in
large numbers to feed on those rare
feasts. Here we also find Mariana
snailfish and kusk eels, the deepest
known fish on Earth.
The word known is the key part of that
sentence because there is so much that
we don't know about these deepest parts
of the ocean. There could be other fish
living in these deep waters or even
deeper, but we just haven't discovered
them yet. Finding anything at all is
more a case of luck than endeavor. Here
we find what look like large lumps of
jelly sticking out the rocks.
Xeno fires, single cellled organisms
that grow to a size of 20 cm or more.
About the size of a football. That is
crazy for a single cell. Impossible. Yet
here they are. Made possible by an
environment that would destroy cells
found at the surface.
There is an important side to all these
interesting discoveries that we are only
now beginning to realize.
Examples of pushing life to extreme
limits such as the Xeno Firefalls are
where we learn about how cells work, how
the processes inside cells and bodies
can be adapted and changed. And that is
where we learn about life itself.
New medical treatments and cures
frequently originate from the study of
the oddities of life on our planet. And
at these depths, most life that we find
is distinctly odd.
Even here, the sediments hide bristle
worms and decapods such as shrimps that
burrow through the sediment, surviving
on the meager organic particles that
descend from the surface. Above the
silt, we may see cope pods such as free
swimming crustations or sea cucumbers.
But as we descend deeper from the
surface, life has become more scarce for
one very good reason. The deeper we go,
the less there is available to support
life.
As we leave this higher level of the
trench floor and descend a further 3 km
down into the deepest waters on Earth,
this effect becomes even more
pronounced. We leave the Mariana
snailfish and cusk eels behind. This
water is just too deep for any fish, or
at least that is what is currently
believed. But we simply don't know.
There has been so little meaningful
exploration that I would be dishonest if
I claim to know much about what exists
in the very deepest parts of our oceans.
At the time of making this video, 27
people have visited the Challenger Deep.
That's more than have visited all the
other trenches on the planet combined,
an area larger than Australia. Most of
these dives have been little more than
extreme tourism with little scientific
value.
Tying a dead fish to a pole in front of
a camera and taking it down to just one
place on the planet's surface again and
again and seeing what comes along to eat
it tells us almost nothing. What people
have seen when they've done this are a
few amphipods and sea slugs. That
certainly doesn't mean there's nothing
else down there. It just tells us that
these are the only things attracted to a
dead fish tied to a pole which dutifully
turn up in front of the cameras so we
can see them. If anything, this merely
raises the question of what are we not
seeing? Imagine that everything we know
about the Grand Canyon is from what we
could see by dropping a camera down into
the same place just a few times at night
with a light that only illuminates a
small area in the darkness. Maybe we
could take a small basket down too,
which brings up a spider and a few ants.
Would that tell us much about the Grand
Canyon and what lives there? Of course
it wouldn't. But that is a realistic
comparison of how we've explored the
deepest oceans, an area almost 700 times
bigger than the Grand Canyon.
Only 400 species have been identified in
the Hadel zone. That is everything that
has been found in all the deepest waters
on the entire planet. You may think 400
is quite a lot, but compare that to the
thousands that you'll find in a typical
freshwater lake. In ecological terms,
400 is almost nothing.
Our deep oceans are an extremely
difficult environment to explore. They
are remote and cover a vast area. And
the equipment needed to research the
waters and the sea floor has to
withstand exceptional conditions. But
let me put this into perspective. We've
sent people to the moon. We've sent
vehicles to explore Mars, Saturn, even
Neptune on the edge of our solar system.
Why do we still know so little about an
area that covers more than half of our
own planet? What secrets remain hidden
in the darkest depths of our oceans? I
would love to think that the scientists
desperate to research these fascinating
deep waters will be given the means to
do so. And if and when they do, we'll
bring you the amazing videos, the
discoveries that they make, the
scientific breakthroughs revealed by
making these dark places light.