Earth’s deepest trench presses harder than a thousand atmospheres
The Mariana Trench, a crescent about 2,550 by 69 kilometres in the western Pacific east of the Mariana Islands, holds Earth’s deepest known seafloor at 10,935 ± 6 metres in Challenger Deep. Bottom pressure nears 1,086 bar—over a thousand times sea-level air—while water sits only 1 to 4 °C.
Named for the nearby Marianas (after Queen Mariana of Austria), the trench marks where the Pacific plate dives beneath the Mariana plate in the Izu–Bonin–Mariana system; some subducting crust is up to 170 million years old. Flux melting from that dive built the volcanic island arc. The 1875 Challenger expedition first sounded here with weighted rope; Challenger II’s 1951 echo sounding fixed Challenger Deep near 10,900 metres.
Later surveys disagreed by tens of metres: Vityaz claimed 11,034 m in 1957, Japan’s Takuyō about 10,924 m in 1984, Kaikō reached 10,911 m in 1995, and 2009 Kilo Moana mapping suggested 10,971 m. A 2011 US Navy multibeam map covered the whole trench at 100-metre resolution and spotted four rocky outcrops thought to be former seamounts. Challenger Deep itself lies in Micronesia’s EEZ, outside the 2009 US Mariana Trench Marine National Monument.
Trieste carried Don Walsh and Jacques Piccard to the bottom on 23 January 1960; James Cameron’s Deepsea Challenger followed on 26 March 2012 to 10,908 m. By 2022, twenty-two crewed and seven uncrewed descents were on record. Single-celled monothalamea have been found at 10.6 kilometres depth. Victor Vescovo made four dives in the Limiting Factor across late April and early May 2019, logging 10,928 metres and becoming the first person to revisit the Deep; in 2022 the same craft took Dawn Wright down as the first Black woman to explore the trench, and a beer bottle was spotted on the floor.
Life down there keeps surprising researchers. Piccard's reported flatfish is now widely doubted and may have been a sea cucumber, but 2011 drop cameras filmed xenophyophores wider than 10 centimetres, the largest known single cells. A snailfish seen at 8,145 metres in 2014 set a record for the deepest fish on video, and three 2025 papers in Cell counted over 7,000 microbial species, 89 percent unknown to science. Humanity has arrived too: crustaceans hauled up in 2016 carried heavy loads of PCBs, a toxin banned in the 1970s, and every amphipod examined had synthetic fibres in its gut.
Source: Mariana Trench
