How deep is the Ocean?

The world's deepest point in the oceans is the Challenger Deep which is found within the Marianas Trench. The Marianas Trench is a depression (deep cracks) in the floor of the western Pacific Ocean. Marianas Trench is formed (as other ocean trenches) as a result of the oceanic plate being pushed against a continental plate whereby causing the oceanic plate to pushed downward making deep fissure. Its location is east of the Mariana Islands and is 1,554 miles long and averages 44 miles wide (see diagrams below). The Marianas Trench depth is 36,200 feet (11,033 m or 11.03 km).

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Marianas Trench is far (miles) beyond the reaches of sunlight where it can no longer penetrate the ocean. The seas' pressures at this depth is unimaginable. It is 8 tons per square inch or 16,000 pounds on every square inch. At this depth it also has very cold temperatures along with darkness. Imagine an underwater depth that is higher than the Eiffel Tower in Paris, France which is 1,052 ft (321m) or the Empire State building in New York, US which is 1,472 ft (449). It could take 5.4 Empire State Buildings in order to reach the bottom of the deepest ocean - the Mariana Trench. Better yet, the world's highest mountain, Mount Everest (29,141 feet), would be covered by over 1.25 miles of water.

Beneath this ocean surface at such a depth, lies an alien dark cold world with its own life where very eerie looking fishes and other life form can be found. It was once thought to be a lifeless place when it was discovered by the British survey ship Challenger II in 1951 (where it got its name). This belief of the deepest point on Earth being lifeless was however proven wrong in 1960 when Jacques Piccard and Navy Lt. Donald Walsh descended in the U.S. Navy Trieste, a bathyscaphe ("bathy" = deep & "scaphe" = ship), to the bottom of the Mariana Trench - Challenger Deep. The first and still the only manned vessel to go to its bottom. They provided the measurement for the depth of the Mariana Trench. Unmanned vessels have also recorded its measurement although they do not go as far as the Trieste.

-From the Did You Know? site: