Ocean Depths

The oceans cover about 71 percent of the Earth's surface. The three main oceans are the Pacific, with an area of approximately 102 million miles is greater than all of the continents combines; the Atlantic Ocean and the Indian Ocean, The Arctic and Antarctic oceans around the poles are really just an extension of these three main oceans.

The average depth of the ocean is about 14,000 feet. The deepest point, in the Marianas Trench in the Pacific Ocean is 36,197 ft below the surface. The ocean trenches are places where one plate is being pushed down beneath another, other plate edges in the oceans are in the centers of the oceanic ridges where new rock is being formed from magma in the central rift valleys. The largest oceanic ridge is in the Atlantic. It is 9942 miles long and 497 wide. Its highest peak is Mount Pico in the Azores, which rises 23,615 ft from the ocean floor. Beyond the ridges are flat abyssal plains and in some places abyssal hills.

Isolated mountains rising from the abyssal plains are called seamounts. The world's highest mountain, measured from the base, is Mauna Kea, a volcano on the island of Hawaii in the Pacific Ocean. Mauna Kea is 13,795 ft above sea level, but another 19,678 ft is hidden below the surface of the ocean. This gives Mauna Kea a total height of 33,474 ft.

Around most continents are gently sloping continental shelves. At the edge of these shelves are steep continental slopes. At the bottom of these slopes are more gently sloping continental rises. They are composed of sediments brought from the land by underwater currents, called sub-marine density currents. Deep canyons cut some continental slopes, which have been worn out by the sub-marine density currents, such as the one formed by the muddy water of the Zaire River in Africa.