The average depth of the oceans is about 4 km. More precisely the average depth is 3,688 meters (12,100 ft). Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep. “Deep ocean,” which is anything below 200 meters (660 ft.), covers about 66% of Earth's surface. This figure does not include seas not connected to the World Ocean, such as the Caspian Sea. The deepest point in the ocean is the Mariana Trench, located in the Pacific Ocean near the Northern Mariana Islands. Its maximum depth has been estimated to be 10,971 meters (35,994 ft). The British naval vessel Challenger II surveyed the trench in 1951 and named the deepest part of the trench the “Challenger Deep”. In 1960, the Trieste successfully reached the bottom of the trench, manned by a crew of two men. The press release stated that they planned to dive the Mariana Trench (Pacific Ocean, 11,033 m), Molloy Deep (Arctic Ocean, 5608 m), Puerto Rico Trench (Atlantic Ocean, 8605 m), South Sandwich Trench (Southern Ocean, 7235 m) and the Diamantina Trench (Indian Ocean, 8047 m).“The intense pressures in the deep ocean make it an extremely difficult environment to explore.” Although you don't notice it, the pressure of the air pushing down on your body at sea level is about 15 pounds per square inch. If you went up into space, above the Earth's atmosphere, the pressure would decrease to zero.