The Geology and Life Forms of the Abyss
The ocean floor was long thought to be a barren, featureless “desert.” It seemed unlikely that the cold, black depths could be hiding anything of interest or sustaining any form of life. People referred to the deep ocean as the abyss, from the Greek word abyssos, which means “without bottom.” But as scientists began to explore ever farther beneath the ocean surface in the 1900's, it became clear that the abyss holds many interesting secrets and that its geology is strikingly varied.
If all the water could be removed from the world ocean, the continents would look like high plateaus rising above the sea floor, each bordered by a relatively shallow, gently sloping plain called a continental shelf. The continental shelves are hundreds of miles wide in some places, and nearly nonexistent in others. At a depth of about 90 to 180 meters (300 to 600 feet), the continental shelves drop off steeply to the abyss. The average depth of the ocean beyond the continental shelves is about 4,800 meters (16,000 feet), but this figure is somewhat deceptive because the ocean floor includes many tall submerged mountains as well as trenches that can be 5 to 11 kilometers (3 to 7 miles) deep.