Mariana Trench
The Mariana Trench is the deepest known submarine trench. It is located in the floor of the western North Pacific Ocean, to the east of the Mariana Islands.The trench has a maximum depth of 10,924 m (35,840 ft). It was fully surveyed in 1951 by the British navy vessel, Challenger II, which gave its name to the deepest part of the trench, the Challenger Deep. The trench is the boundary where the Pacific tectonic plate meets the Philippine Plate. The bottom of the trench is further below sea level than Mount Everest is above sea level.
In an unprecedented dive, the U.S. Navy bathyscaphe Trieste reached the bottom at 1:06 pm on January 23, 1960 with U.S. Navy Lt. Don Walsh and Jacques Piccard. Iron shot was used for ballast, with gasoline for buoyancy. The onboard systems indicated a depth of 37,800 ft (11,521 m), but this was later revised to 35,800 ft (10,912 m). At the bottom Walsh and Piccard were surprised to discover sole or flounder about one foot (300 mm) long, as well as shrimp. According to Piccard, "The bottom appeared light and clear, a waste of...firm diatomaceous ooze."
A Japanese robotic deep-sea probe, known as Kaiko, broke the depth record for unmanned probes when it reached the bottom of the Challenger Deep on 24 March 1995. Created by the Japan Marine Science and Technology Center (JAMSTEC), it was one of the rare few unmanned deep-sea probes in operation that could dive deeper than about 19,680 feet. It's recorded depth of 10,911 m (35,797 ft) for the Challenger Deep, may be the most accurate measurement taken yet. Sadly, Kaiko was lost at sea on 29 March 2003, after just more than 8 years of service, when one of the secondary cables snapped during an approaching typhoon. Currently no other operational vehicle exists that is capable of reaching the same depths.
At the bottom of the Mariana Trench, water exerts a pressure of 1086 bar (108.6 MPa or 15,931 lb/in²).