<P> The Mariana Trench is a site chosen by researchers at Washington University and the Woods Hole Oceanographic Institution in 2012 for a seismic survey to investigate the subsurface water cycle . Using both ocean - bottom seismometers and hydrophones the scientists are able to map structures as deep as 97 kilometres (60 mi) beneath the surface . </P> <P> Four descents have been achieved . The first was the manned descent by Swiss - designed, Italian - built, United States Navy - owned bathyscaphe Trieste which reached the bottom at 1: 06 pm on 23 January 1960, with Don Walsh and Jacques Piccard on board . Iron shot was used for ballast, with gasoline for buoyancy . The onboard systems indicated a depth of 11,521 m (37,799 ft), but this was later revised to 10,916 m (35,814 ft). The depth was estimated from a conversion of pressure measured and calculations based on the water density from sea surface to seabed . </P> <P> This was followed by the unmanned ROVs Kaikō in 1996 and Nereus in 2009 . The first three expeditions directly measured very similar depths of 10,902 to 10,916 m (35,768 to 35,814 ft). The fourth was made by Canadian film director James Cameron in 2012 . On 26 March, he reached the bottom of the Mariana Trench in the submersible vessel Deepsea Challenger . </P> <P> In July 2015, members of the National Oceanic and Atmospheric Administration, Oregon State University, and the Coast Guard submerged a hydrophone into the deepest part of the Mariana Trench, the Challenger Deep, never having deployed one past a mile . The titanium - shelled hydrophone was designed to withstand the immense pressure 7 miles under . Although researchers were unable to retrieve the hydrophone until November, the data capacity was full within the first 23 days . After months of analyzing the sounds, the experts were surprised to pick up natural and man - made sounds such as boats, earthquakes, a typhoon, and baleen whales . Due to the mission's success, the researchers announced plans to deploy a second hydrophone in 2017 for an extended period of time . </P>

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