The Mariana Trench: Life at the Bottom of the Worlds Deepest Abyss

Eleven Kilometers Below the Waves

The Challenger Deep, located in the southern end of the Mariana Trench, reaches approximately 10,935 meters (35,876 feet) below sea level. If Mount Everest were placed at the bottom, its peak would still sit more than 2,000 meters beneath the surface. The trench stretches 2,550 kilometers across the western Pacific Ocean, east of the Mariana Islands, forming an arc-shaped depression in the ocean floor. Only four crewed expeditions have reached the bottom.

Pressure at the Challenger Deep exceeds 1,086 bars—roughly 1,071 times standard atmospheric pressure at sea level. A human body at that depth would experience a force equivalent to 50 jumbo jets stacked on top of it. Yet life persists there. That fact alone has reshaped scientific understanding of biological limits.

How the Trench Formed

The Mariana Trench sits at a convergent plate boundary where the Pacific Plate subducts beneath the smaller Mariana Plate. The Pacific Plate, among the oldest oceanic crust on Earth at roughly 170 million years, is dense and cold. It descends into the mantle at an angle of roughly 10 to 15 degrees near the surface, steepening to nearly vertical at depth. This subduction created the trench and also fuels the volcanic arc of the Mariana Islands to the west.

The trench is not the only deep feature in the area. The Sirena Deep, located roughly 200 kilometers east of the Challenger Deep, reaches 10,714 meters. Several other points along the trench exceed 10,000 meters.

Expeditions to the Bottom

On January 23, 1960, Swiss oceanographer Jacques Piccard and U.S. Navy Lieutenant Don Walsh descended to the Challenger Deep aboard the bathyscaphe Trieste. The dive took 4 hours and 47 minutes. They spent 20 minutes on the bottom before a cracked outer window forced an early ascent. Through the porthole, Piccard reported seeing a flat fish on the seafloor—evidence of vertebrate life at maximum depth that was disputed for decades.

No crewed vessel returned for 52 years. In 2012, filmmaker James Cameron piloted the Deepsea Challenger solo to the bottom, spending roughly three hours collecting samples and filming. In 2019, explorer Victor Vescovo made four dives in the submersible Limiting Factor, reaching 10,928 meters on his deepest descent and discovering plastic waste at the bottom of the ocean.

• The Trieste used gasoline-filled floats for buoyancy and iron shot ballast for descent
• Cameron’s craft was a vertical torpedo design, just 1.1 meters wide at the pilot sphere
• Vescovo’s Limiting Factor was the first commercially certified full-ocean-depth submersible
• Unmanned remotely operated vehicles (ROVs) have visited the Challenger Deep multiple times since 1995
• China’s Fendouzhe submersible reached 10,909 meters in November 2020 with three crew members

Life Under Extreme Pressure

The hadal zone—ocean depths below 6,000 meters—was once assumed to be lifeless. Sampling expeditions have proven otherwise. The Mariana Trench hosts bacteria, foraminifera (single-celled organisms with shells), amphipods (shrimp-like crustaceans), and xenophyophores (giant single-celled organisms that can exceed 10 centimeters across).

Amphipods of the genus Hirondellea are among the most studied hadal organisms. They thrive at depths exceeding 10,000 meters, feeding on organic material that sinks from the surface—a process called marine snow. Their cells contain high concentrations of trimethylamine N-oxide (TMAO), a compound that stabilizes proteins against pressure-induced deformation.

In 2023, scientists confirmed the deepest fish ever recorded: a juvenile snailfish filmed at approximately 8,336 meters in the Izu-Ogasawara Trench near Japan. The Mariana Trench itself has yielded snailfish sightings at around 8,178 meters. Below that depth, the fish body plan appears unable to function, and the trench floor belongs to invertebrates and microbes.

Pollution Reaches the Abyss

Victor Vescovo’s 2019 expedition found a plastic bag and candy wrappers at 10,928 meters. Subsequent studies detected microplastics in sediment samples and in the digestive tracts of hadal amphipods. A 2020 study in the journal Marine Pollution Bulletin reported persistent organic pollutants, including PCBs, in amphipod tissues from the Mariana Trench at concentrations comparable to those found in industrialized coastal waters.

• Microplastic fibers were found in every sediment sample tested from the trench floor
• PCB concentrations in trench amphipods exceeded levels found in some coastal crabs
• Mercury contamination has been detected in sediment cores from hadal depths
• Sinking particles transport surface pollutants to the deep ocean over months to years

Scientific and Strategic Significance

The Mariana Trench is part of the Mariana Trench Marine National Monument, designated by the United States in 2009 and covering roughly 246,000 square kilometers of seafloor and water column. The designation prohibits mining and commercial extraction but does not prevent scientific research.

Deep trench research has practical implications beyond biology. Subduction zone dynamics influence earthquake and tsunami risk across the Pacific. Sediment analysis provides records of past climate and ocean chemistry. Extremophile enzymes from hadal organisms have potential applications in industrial biotechnology. The deepest place on Earth is not a dead end. It is a frontier where geology, biology, and human impact intersect at pressures that would crush steel, in darkness that has persisted since the ocean formed.