The Mariana Trench, in the western Pacific Ocean, is the deepest known oceanic trench on Earth. Located approximately 200 kilometers (124 miles) east of the Mariana Islands, this crescent-shaped abyss stretches for about 2,550 kilometers (1,580 miles) with an average width of 69 kilometers (43 miles). Its deepest point, the Challenger Deep, plunges to a maximum known depth of 10,984 ± 25 meters (36,037 ± 82 feet). This depth surpasses the height of Mount Everest by over 2 kilometers.
The Trench’s Extreme Conditions
Life at the bottom of the Mariana Trench endures extreme conditions. The immense pressure at these depths reaches approximately 1,086 bar (15,750 psi), over 1,000 times the standard atmospheric pressure at sea level. This crushing force is comparable to eight tons per square inch or thousands of elephants standing on a car. Temperatures in the trench are consistently near freezing, typically ranging from 1 to 4 °C (34 to 39 °F).
Sunlight is completely absent, meaning organisms must rely on senses other than sight to navigate and find food. Food scarcity is another significant challenge, with sustenance primarily arriving as “marine snow,” or organic material drifting down from shallower waters. These factors create a unique and hostile habitat.
Life Adapted to the Deep
Despite these conditions, the Mariana Trench supports a variety of life forms with remarkable adaptations. Many deep-sea organisms have incompressible bodies, like the exoskeleton of amphipods, to withstand immense pressure. Their cellular membranes contain unsaturated fats that remain fluid at near-freezing temperatures, preventing solidification. Specialized enzymes also enable biochemical processes to function efficiently under high pressure.
Organisms found here include hadal amphipods, shrimp-like crustaceans that can grow nearly a foot long. The Mariana snailfish (Pseudoliparis swirei) is the deepest-living fish species, found at depths exceeding 8,000 meters. These translucent fish adapt their lipid and protein metabolism to efficiently store energy and maintain membrane fluidity. Microbes and single-celled organisms, such as monothalamea (a type of giant amoeba), also thrive, feeding on methane and sulfur seeping from the crust or relying on marine snow.
Submarine Landscape and Geology
The seafloor of the Mariana Trench presents a landscape shaped by geological forces. It features a V-shaped profile with steep walls that extend for several kilometers, featuring cliffs, ridges, and peaks. The trench formed as a result of subduction, where the older, denser Pacific Plate is forced beneath the smaller Mariana Plate.
Sediments at the bottom are typically fine-grained mud and detritus settled from upper ocean layers. The lack of sunlight and limited organic material contribute to slow sedimentation rates, preserving ancient marine deposits. The trench is also part of the Pacific Ring of Fire, a geologically active region prone to earthquakes and volcanic activity, which influences its terrain.
Pioneering Expeditions and Discoveries
Human exploration of the Mariana Trench has gradually revealed its secrets. The first crewed descent occurred on January 23, 1960, when Jacques Piccard and Don Walsh piloted the Bathyscaphe Trieste to the Challenger Deep, reaching 10,916 meters. Their brief 20-minute stay provided the first direct observation of life at full ocean depth, with reports of seeing what they believed was a flatfish, likely a sea cucumber.
In March 2012, filmmaker James Cameron made the first solo dive in his submersible, Deepsea Challenger, reaching 10,908 meters. His expedition collected samples and captured images, offering new insights into the trench’s geology and biology. More recently, Victor Vescovo, in his submersible Limiting Factor, conducted multiple dives in 2019, including a record-breaking descent to 10,928 meters. These missions have expanded our understanding of deep-sea life and geology, and made discoveries such as the presence of plastic debris, including single-use plastic bags and microplastics, even at the deepest points.