Ocean

Generally, the whole body of salt water which covers nearly three fourths of the surface of the globe. The average depth of the ocean is estimated to be about 13,000 feet (3,960 meters); the greatest reported depth is 34,218 feet (10,430 meters), north of Mindanao in the Western Pacific Ocean. The ocean bottom is a generally level or gently undulating plain, covered with a fine red or gray clay, or, in certain regions, with ooze of organic origin. The water, whose composition is fairly constant, contains on the average 3½ percent of dissolved salts; of this solid portion, common salt forms about 78 percent, magnesium salts 15–16 percent, calcium salts 4 percent, with smaller amounts of various other substances. The density of ocean water is about 1.026 (relative to distilled water, or pure H2O). The oceans are divided into the Atlantic, Pacific, Indian, Arctic, and Antarctic Oceans. See Oceans (World).