Full transcript
Introduction
0:12The deep sea is a world of extremes. So far in this series, we’ve taken a look at the
0:20ways in which animals have adapted to survive in the cold, dark depths. We’ve explored
0:26the ecosystems of this unforgiving realm, and seen how communities of life cling to
0:33whatever source of energy they may find, from vents of superheated water, to the carrion
0:39of sunken whales. But now it’s time to dive even deeper, and discover a place where life
0:48is pushed to its absolute limits. For at the bottom of the Pacific Ocean, the sea floor
0:56widens into a gaping abyss of obscurities. Fish that seem to lack faces, sprawling fields
1:05of bacteria, and giants that resemble life from another planet. Let’s take a closer
1:13look at the hidden world of the Mariana Trench.
Chapter 1: Gates of the Underworld - How the Trench Formed
1:29The infamous Mariana Trench sits like a crescent-shaped dent in the floor of the Pacific. A 2,550
1:38km long, 69 km wide fracture that plummets down into a pure black void. At the bottom,
1:49it hosts the deepest known location on Earth. The Challenger Deep, 11,033 metres or 36,200
2:00feet beneath the waves. The trench itself is but one part of a global network of deep
2:08scars that cut across the ocean floor. Features that formed from a process called subduction.
2:17In the case of the Mariana Trench, the western edge of the Pacific Plate was thrust beneath
2:23the smaller Mariana Plate to the west, creating the deep fracture. Molten material then rose
2:32through volcanoes near the trench, building the nearby Mariana Islands.
Chapter 1: Gates of the Underworld - An 'Impossible' Frontier
2:42At its deepest point, the Mariana Trench dips down into a little-explored zone of the ocean.
2:51The Hadal zone, named after the realm Hades, the underworld of Greek Mythology. A suitable
2:59title for a place where the conditions of pure darkness, acidic freezing water, scarce
3:06food, and immense pressure create a challenging environment for creatures to survive in. For
3:14much of history, it was believed to be a dead zone, void of any life at all. An impossible
3:24frontier and an empty void of perils that could never be reached by any human. But in
3:34the 19th Century, this was all about to change.
Chapter 1: Gates of the Underworld - The HMS Challenger
3:40The Mariana’s depths were first plumbed in 1875 when the crew aboard the H.M.S Challenger
3:47cast a weighted sounding rope over the side of the vessel and found they needed more rope.
3:54They had not expected there to be a location so deep, but news its discovery caught the
4:01eye of the ambitious. Knowing it existed simply wasn’t enough, and a few dared to venture
4:09to the bottom.
Chapter 2: In Pursuit of the Abyss - The Bathyscape Trieste, 1960
4:18In 1960, 85 years after the Challenger Deep was discovered on that pioneering voyage,
4:26two men set out to reach the bottom. Jacques Piccard and Navy Lt. Don Walsh, sheltered
4:35only by a cramped bathyscape submersible called the Trieste. Their 5-hour descent was fraught
4:43with challenges. The water pressure near the bottom was nearly a thousand times greater
4:49than atmospheric pressure at sea level. During the journey, this caused the viewing window
4:56to crack, limiting their time spent on the sea floor to only 20 minutes. Even in such
5:07a short amount of time, what they saw would shock the scientific community. Life. Pale
5:16shrimp and flounder-like fish, along with what they described as a dark brown diatomaceous
5:22ooze that covered the sea floor.
5:28Piccard described this moment with excitement in a book about the voyage. “Here, in an
5:35instant, was the answer that biologists had asked for the decades. Could life exist in
5:42the greatest depths of the ocean? It could!”
Chapter 2: In Pursuit of the Abyss - The Deepsea Challenge, 2012
5:51When James Cameron followed in the Trieste’s footsteps onboard the Deepsea Challenger in
5:562012, he too saw the sprawling microbial mats — bizarre-looking, filamentous clumps of
6:04microorganisms living off chemicals from altered rocks 10,912 meters (35,803 feet) down in
6:12a sunless world. It is these bacteria that support more complex creatures, for without
6:23sunlight, larger animals must instead rely on the energy produced by bacteria undergoing
6:29chemosynthesis. The deep sea equivalent to photosynthesis.
Chapter 3: Discoveries in the Dark - The Kaiko Mission
6:54The footage you’re seeing now was taken by an unmanned Japanese submersible called
7:00Kaiko in 1996. Having reached a depth of 10,897 metres, it marked the deepest dive for an
7:12unmanned submersible at the time. Its goal was to sample bacteria from the matts that
7:18Piccard and Walsh had observed nearly 40 years earlier. They found that a number of these
7:25bacterial species appeared to be obligately barophilic, meaning they thrived under high
7:31environmental pressures, proving that our idea that life could only exist in more moderate
7:37conditions was flawed. But in 1998, Kaiko returned to the Challenger Deep and stumbled
7:46upon more complex life. Hirondellea gigas, a gigantic amphipod species.
7:55This discovery posed a bit of a mystery. The extreme pressures of the deep sea cause the
Chapter 3: Discoveries in the Dark - The Hadal Amphipod
8:02calcium carbonate that makes up the shells of amphipods and many marine animals to dissolve
8:07more readily in water, leaving their soft bodies vulnerable. As such, amphipods are
8:13not usually found below about 5,000 m (16,400 feet). And yet here in Kaiko’s lights was
8:22a giant amphipod, retaining even its tough exoskeleton. It’s since been found that
8:29they protect their shells using a form of aluminium armour, using chemicals in their
8:35gut to extract aluminium ions from the seafloor mud while they forage for food.
8:44In their role as detrivores, these amphipods occupy a key role in the ecosystem. They act
8:51as a clean-up crew, possessing enzymes that are able to digest even wood.
Chapter 3: Discoveries in the Dark - Abyssal Sea Cucumbers
9:04In more recent times, remote submersibles have caught yet more oddities of the Mariana
9:09Trench in their headlights. Among the most abundant inhabitants are the holothurians.
9:18Sea cucumbers, like the remarkable sea pig with its ring of feeding tentacles that it
9:23uses to sift through the mud and grab onto food. Some scientists believe Piccard’s
9:31fish was in fact a sea cucumber, for it is thought that fish are unable to survive where
9:37the pressure is so great that it would dissolve the bones of any vertebrates. The deepest
Chapter 3: Discoveries in the Dark - The Mariana Snailfish
9:51known fish thrives at depths of 8,000 meters (26,200 feet), still 2 km above the Challenger
10:01Deep. The Mariana Snailfish, discovered in 2014, yet given the scientific name Pseudoliparis
10:09swirei to commemorate sub-lietunent Herbert Swire from the HMS Challenger.
Chapter 3: Discoveries in the Dark - Denizens of the Abyss
10:20But snailfish and amphipods are not the only oddballs found in the Trench. Gigantic xenophyophores
10:27grow to be 20 cm in diameter, yet consist of only a single cell. Predatory tunicates
10:36called sea squirts anchor their bodies to the sides of canyons in wait of passing prey,
10:42while deep sea hatchetfish use bioluminescence to blend in with their surroundings. While
10:49only glimpses of these otherworldly organisms have been recorded, their abundance goes to
10:54show that life will always find a way to survive, even when faced with the intense challenges
11:02of living at the heart of the ocean’s underworld.
Conclusion
11:13Despite all the expeditions and footage that’s been gathered, we have still only just begun
11:19to dip our toes into the hidden world of the Mariana Trench. It is likely that many new
11:26species await discovery, and will help us piece together the puzzle of how animals can
11:31survive such extremities. Researching the Mariana’s microorganisms could lead to vital
11:38breakthroughs in biomedicine and biotechnology, and shed light on the story of life’s emergence
11:46on planet Earth. But even the furthest depths are within reach of human-driven destruction.
11:56Already has plastic been found in a place we scarcely understand. Who knows what vital
12:04discoveries might vanish before we come to understand their importance.
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