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Mariana Trench: The Deepest Depths

The Mariana Trench, sometimes called the Marianas Trench, is the deepest point in the earth's oceans. The crescent-shaped trench is located in the Western Pacific, just east of the 14 Mariana Islands, near Guam. Its depth has been measured at 36,201 feet (11,034 meters).

This image of the Challenger Deep in the Mariana Trench, the deepest spot on Earth, was made using sound waves bounched off the sea floor. Darker blues represent deeper spots.
This image of the Challenger Deep in the Mariana Trench, the deepest spot on Earth, was made using sound waves bounched off the sea floor. Darker blues represent deeper spots.
Credit: NASA/UNH Center for Coastal and Ocean Mapping/Joint Hydrographic Center

By comparison, Mount Everest stands at 29,026 feet (8,848 meters), meaning the deepest part of the Trench is 7,175 feet (2,186 meters) deeper than Everest is tall. Similarly, the Trench is 1,580 miles (2,542 kilometers) long — more than five times the length of the Grand Canyon. However, the trench is only 43 miles (69 km) wide.

Features of the trench

The Mariana Trench is not the furrow that most of us think of as “trenches.” Instead, it is a subduction zone, a zone where one part of the seabed is pushed below another into the earth's interior. In this case, the Pacific tectonic plate has pushed below the Philippine plate. [Infographic: Tallest Mountain to Deepest Ocean Trench]

Mariana Tranch map
The Mariana Trench is located in the western Pacific Ocean.
Credit: www.freeworldmaps.net

As deep as the trench is, it is not the spot closest to the center of Earth. Because the planet bulges at the equator, the radius at the poles is about 16 miles (25 km) less that the radius at the equator. So, parts of the Arctic Ocean seabed are closer to the Earth's center than the Challenger Deep, the trench's deepest part.

The trench is part of one of the world's oldest seabeds, about 180 million years old. The seabed is covered in a kind of “ooze,” a yellowish, viscous sediment that is composed of the shells and decay from animal and plant plankton.

The water pressure on the floor of the trench is more than 8 tons per square inch (703 kilograms per square meter), the equivalent of having 50 jumbo jets piled on top ofa person. Most of the trench is completely dark.

The trench's floor has hydrothermal vents that emit highly acidic fluids. The temperature around the vents can reach temperatures of 572 degrees F (300 degrees C). Conversely, the water at the seabed floor is very basic and hovers between 34 and 40 degrees F (1.1 and 4.4 degrees C). The contrast between the two creates an ever-changing and nearly-toxic environment. Even so, life thrives.

Life in the trench

Scientists have discovered many different aquatic life forms in the Mariana Trench. Bacteria teem around the thermal vents, and oceanographers have found more than 200 different microorganisms from a mud sample taken from Challenger Deep, the deepest part of the trench. [Video: Dive Deep: Virtual Tour of the Mariana Trench]

At the seabed, single-celled primitive protists (formaminifera)thrive, as do bizarre, translucent, sea-cucumber-like animals called holothurians. Two-inch long (4 cm) amphipods — shrimp-like crustaceans — have also been found in abundance.

Snails and bivalves survive in the trench by developing soft shells because water pressure makes growing hard shells difficult.

Higher up in the trench, 4-inch-long (10 cm), single-celled xenophyophores surround and absorb food and nutrients like amoebas. Fields of bone-white clams have been found dwelling near cooler vents at about 20,000 feet (6,096 meters). Deep-dwelling creatures inhabit the trench at varying depths, including bioluminescent comb jellies, snailfish, and eels.

These creatures experience greater longevity than their counterparts higher up in the ocean. In many cases, they live for more than 100 years.

Humans and the trench

  • In 1875, the trench was discovered by the H.M.S. Challenger using recently invented sounding equipment during a global circumnavigation.
  • In 1951, the trench was sounded again by H.M.S. Challenger II. Challenger Deep was named after the two vessels.
  • In 1960, a “deep boat” named Bathyscaphe Trieste reached the bottom of Challenger Deep. It was the first vessel to do so and was manned by U.S. Navy Lt. Don Walsh and Swiss scientist Jacques Piccard.
  • In 1995, the Japanese unmanned submarine Kaiko gathered samples and useful data from the trench.
  • In 2009, U.S. President George W. Bush established the Marianas Trench Marine National Monument through Presidential Proclamation, which allowed for the protection and exploration of 95,216 square miles (246,600 sqaure km).
  • Also in 2009, the United States sent a hybrid remotely operated vehicle, Nereus, to the floor of Challenger Deep. The vehicle remained on the seabed for nearly 10 hours.
  • In 2012, National Geographic explorer and movie director James Cameron manned the DeepSea Challenger and reached the seabed but was unable to capture any photos due to a hydraulic fluid leak.

— Elizabeth Dohrer, LiveScience Contributor

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