The Mariana Trench: Deeper Than Everest Is Tall, and Still Full of Life

Where Two Plates Collide

The Mariana Trench exists because two tectonic plates are colliding in the western Pacific Ocean, and one of them is diving beneath the other. The Pacific Plate, heading west and northwest, is subducting under the Mariana Plate — sinking back into the mantle along a curving line that creates the arc-shaped Mariana Islands above sea level and the trench in the seafloor below.

The deepest point of the trench, called Challenger Deep, lies in the southern part of the Mariana Trench, approximately 320 kilometers southwest of Guam. Its depth has been measured repeatedly with improving technology since the British survey ship HMS Challenger first sounded it in 1875 and found water over 8,000 meters deep. Modern sonar measurements using multibeam echo sounders have refined the depth to approximately 10,924 to 11,034 meters below sea level, depending on the method and correction factors applied.

At this depth, the pressure reaches approximately 1,100 times standard atmospheric pressure — about 11 tonnes pressing down on every square centimeter. The temperature is near 2°C. No sunlight penetrates anywhere near this depth; the environment is completely dark.

Life at the Extreme

Despite these conditions, the Challenger Deep is not lifeless. This was one of the significant scientific revelations of deep-ocean exploration: life exists at every depth the ocean reaches. Bacteria and other microorganisms have been found in sediment samples from the trench bottom. More dramatically, single-celled organisms called foraminifera — some reaching several centimeters in size, unusually large for their type — were found living at the deepest point.

Small crustaceans called amphipods have been collected from the trench in large numbers, apparently thriving in the cold, high-pressure environment. These organisms feed on the organic matter — dead plant and animal material — that falls from the surface ocean and accumulates at the bottom, creating an ecosystem that depends entirely on energy arriving from above rather than from sunlight or hydrothermal vents.

More recently, fragments of plastic have been found in the digestive systems of amphipods collected from the Challenger Deep — a finding that attracted significant attention because it demonstrated that human pollution has reached even the most remote and inaccessible point on the planet.

The Humans Who Went to the Bottom

The Challenger Deep has been visited in person only a handful of times in history, each visit a significant engineering achievement.

In 1960, Jacques Piccard and Don Walsh descended to the bottom in the bathyscaphe Trieste, a vessel built like an underwater balloon with a steel observation sphere suspended beneath a large float. They reached approximately 10,916 meters, spending 20 minutes on the bottom before ascending. They observed a flatfish near the bottom, suggesting vertebrate life at extreme depth — an observation later disputed but never definitively settled.

In 2012, filmmaker and explorer James Cameron descended alone in a specially designed submersible called Deepsea Challenger, spending three hours on the bottom and collecting samples and footage. He reported a nearly featureless landscape of flat, brown sediment extending in every direction.

In 2019, investor and explorer Victor Vescovo set a new depth record with a descent in the submersible Limiting Factor to 10,928 meters, surpassing previous records and carrying out extensive scientific sampling across multiple dives.

The Mariana Trench's depth makes it a symbol of the unconquered and unknown — a reminder that the ocean, which covers 71 percent of Earth's surface, has been explored in detail for only a tiny fraction of its total volume.

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