It has a maximum depth of 10,924 m (35,838 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 US 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, but this was later revised to 35,800 ft. At the bottom Walsh and Piccard were surprised to discover sole or flounder about one foot (30 cm) long, as well as shrimp. According to Piccard, "The bottom appeared light and clear, a waste of ... firm diatomaceous ooze."
At the bottom of the Marianas Trench water exerts a pressure of 1086 bar (15,931 lb per square inch).