The deepest spot in the ocean could swallow Everest with a mile to spare

Roughly 200 kilometers east of the Mariana Islands in the western Pacific, the seafloor drops away into a crescent-shaped gash more than 2,500 kilometers long. At its deepest point, a narrow slot known as Challenger Deep, the water column above measures 10,935 meters, making it by a wide margin the deepest known place in any ocean on the planet. That single number is hard to picture in isolation, but the comparison scientists reach for most often puts it in context immediately: stack Mount Everest at the bottom, and its summit would still sit more than two kilometers underwater.

A crescent scar formed by one plate diving under another

The trench exists because of plate tectonics, specifically the point where the Pacific plate, some of the oldest and densest oceanic crust on Earth at up to 170 million years old, is forced beneath the smaller Mariana plate to its west. That subduction process is also what built the Mariana Islands themselves, as water trapped in the sinking crust triggers melting in the mantle above it and feeds a chain of volcanoes along the island arc. The trench marks the deepest expression of that same collision, running for roughly 2,550 kilometers with a maximum width near 69 kilometers, according to published geological surveys of the feature.

Pressure enough to crush bone, cold enough to number in single digits

Conditions at Challenger Deep are hostile by any human standard. The water column exerts roughly 1,086 bars of pressure at the bottom, more than a thousand times atmospheric pressure at sea level, while the water itself sits at a near-freezing one to four degrees Celsius. No sunlight reaches that depth at all, which rules out photosynthesis as an energy source for anything living there and forces the local food web to depend instead on organic material drifting down from far above, along with chemical energy released at nearby hydrothermal vents and mud volcanoes.

From a weighted rope in 1875 to a titanium submersible

The Mariana Trench was first measured in 1875 by the crew of the HMS Challenger, whose weighted sounding line recorded a depth of roughly 8,184 meters using nineteenth-century equipment that could only approximate the true bottom. Sonar and echo-sounding surveys through the twentieth century gradually refined that figure toward the modern value, and in 1960 the bathyscaphe Trieste carried two men, Jacques Piccard and Don Walsh, to the bottom in the first crewed descent, a feat not repeated by a human crew until film director James Cameron’s solo dive in 2012. Since then, explorer Victor Vescovo has returned to Challenger Deep multiple times using a modern titanium-hulled submersible, reaching a record depth of 10,928 meters in April 2019 and becoming the first person to dive the trench more than once, at one point bringing geographer Dawn Wright along as the first Black woman to reach the trench floor. Measurements have not always agreed: a 1957 Soviet survey reported a depth of 11,034 meters at a site it called the Mariana Hollow, well beyond the figures recorded before or since, and a separate location discovered between 1997 and 2001 by researchers surveying near Guam, later named the HMRG Deep after the team that found it, turned out to be nearly as deep as Challenger Deep itself, underscoring how much of the trench floor still has not been mapped in detail.

Life that never sees the surface

Despite the darkness and pressure, Challenger Deep is not empty. Researchers have recorded single-celled organisms called xenophyophores, among the largest single cells known to science, thriving at extreme depth, along with a species of snailfish filmed in 2014 at more than 8,100 meters that set a new record for the deepest fish ever observed on camera. Microbial life appears to persist even in the trench’s sediment, and expeditions using drop cameras and remotely operated vehicles have documented shrimp, sea cucumbers and jellyfish adapted to pressure and cold that would be lethal to most surface-dwelling species within moments.

A hydrophone that recorded typhoons and whale calls

In July 2015, a team from the National Oceanic and Atmospheric Administration, Oregon State University and the U.S. Coast Guard lowered a titanium-shelled hydrophone into Challenger Deep, the first time anyone had placed a listening device that deep in the ocean. The instrument’s data capacity filled within 23 days, and researchers who retrieved it months later found it had captured a mix of natural and human sound: distant earthquakes, the rumble of typhoons passing far overhead, calls from baleen whales, and engine noise from passing ships, all audible even at nearly seven miles down. The recordings surprised the team, who had expected the deepest point in the ocean to be close to silent given how little energy typically reaches it from the surface.

A protected monument split across two jurisdictions

In 2009, the United States designated the Mariana Trench Marine National Monument to protect the portions of the trench that fall within the U.S. exclusive economic zone surrounding the Mariana Islands, an area managed in part by the National Oceanic and Atmospheric Administration’s fisheries service, which oversees habitat protections across the monument, as described in its Mariana Trench Marine National Monument overview. Challenger Deep itself falls outside that boundary, sitting instead within the exclusive economic zone of the Federated States of Micronesia, meaning the single deepest point on Earth is protected, if at all, under an entirely different country’s jurisdiction than the trench surrounding it.

This article was produced with the assistance of AI and reviewed by an editor.

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