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Deepest Part of the Ocean

The deepest part of the ocean is the Mariana Trench, an oceanic trench located in the Pacific Ocean near the island nation of Guam. At its deepest point, known as the Challenger Deep, the Mariana Trench is almost seven miles (11 kilometers) below sea level. Just to put that in a frame of reference, if we were to shave Mount Everest off the surface of the Earth and drop it into the Mariana Trench, it would disappear, buried in over a mile of water.

As you might imagine, the pressure in the Mariana Trench is extreme: about 1,000 times the atmospheric pressure at sea level. Organisms like humans which are accustomed to life at sea level would implode within fractions of a second if exposed to that depth, and the creatures which live in the Mariana Trench demonstrate a number of unusual adaptations which help them cope with the pressure. Algae, bacteria, marine worms, and an assortment of other unusual creatures live in the total darkness and extreme cold of the Mariana Trench, interrupted only occasionally by survey submarines sent to explore the deepest part of the ocean for science.

This incredibly deep ocean trench has formed at what is known as a convergent plate boundary. The deepest part of the ocean is formed by the subduction of the Pacific Plate under the Philippine Plate. To get an illustration of what the trench looks like, you can slide one of your hands under the other. Right along the boundary where your hands meet, you will notice that a notably deep trough is formed; if you magnify that significantly, you get an idea of what the deepest part of the ocean looks like.

The first survey of the Mariana Trench was undertaken in 1951 by a British team on board the Challenger II. Since the team discovered the deepest point of the trench, the Challenger Deep was named after them. A United States Navy bathysphere visited the bottom of the trench in 1960 with two men on board. Oceanographers liken this expedition to the first moon landing, because of the immense amount of preparation and danger involved, and some like to point out that more is known about the surface of the moon than the deepest part of the ocean.

The Mariana Trench isn't the only deep ocean trench, although it is certainly the deepest, extending to twice the average depth of the world's oceans. Given the extreme conditions at the Mariana Trench, it's unlikely that you will be spending any time there, but if you do, you will be able to see a fascinating array of marine organisms which have only been seen by a handful of human beings.

Unmanned Sub Touches Deepest Part of World's Ocean

An unmanned robotic vehicle has successfully touched the deepest known part of the ocean floor, U.S. researchers revealed on Wednesday.

On May 31, the Nereus was launched off the research vessel Kilo Moana in the western Pacific Ocean, between Papua New Guinea and Japan.

The unmanned aquatic vessel descended 10,902 metres into a part of the Mariana Trench known as Challenger Deep. It is the first vessel to explore the remote area in more than a decade.

"It's the deepest known part of the ocean," said Andy Bowen, project manager of the Woods Hole Oceanographic Institution, which led the dive. "The trench is virtually unexplored, and I am absolutely certain Nereus will enable new discoveries."

With a budget of $8 million US, the Nereus dive was the first voyage into the trench since a Japanese-built robot named Kaiko attempted a voyage in 1998. That robot disappeared when the cable connecting it snapped on a dive during a typhoon in 2003.

Nereus was tested in the waters off the dock of the Woods Hole Oceanographic Institution in Massachusetts in April before being sent to the spot known as Challenger Deep in the Pacific's Mariana Trench. At 11,000 metres below sea level, more than 1,600 metres deeper than Mount Everest is high, Challenger Deep is arguably one of the most remote locations on Earth.  (Tom Kleindinst/Woods Hole Oceanographic Institution)

Measuring a little more than four metres in length, Nereus was able to take pictures and video of the ocean floor and bring back samples of sea life, including shrimp and a sea cucumber.

"The samples collected by the vehicle include sediment from the subducting and overriding tectonic plates that meet at the trench," said Patty Fryer, a geologist with the University of Hawaii.

Water pressure in the trench is more than 1,000 times what it is on land at sea level. The nearly 11,000 metres that Nereus was able to dive is approximately the same as the cruising altitude of a commercial airliner and roughly two kilometres more than the summit of the tallest point on earth, Mount Everest.

"The ocean's deepest regions [were] previously inaccessible" said Julie Morris, the ocean sciences division director of the U.S. National Science Foundation. "We're very pleased with the success of these sea trials."
Connecting tether was the width of a human hair

Nereus was able to succeed where other devices had failed because of a unique new design, researchers say. The unmanned vehicle is remotely operated by pilots aboard a surface ship via a lightweight, micro-thin, fibre optic tether. But Nereus can also be turned into a free-swimming, autonomous vehicle even at great depths.

Conventional diving systems use steel-reinforced cables to maintain control of the probe, but such systems would snap under their own weight in the pressure conditions of the Mariana Trench. The tether the Nereus used during its 10-hour stint on the ocean floor used a combination of fibre optic cables and plastic sheath and was roughly the same diameter as a human hair.

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