At 165,250,000 square kilometers (63,800,000 square miles) in area (as defined with an Antarctic southern border), this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined. The centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North(ern) Pacific Ocean and South(ern) Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific. Its mean depth is 4,000 meters (13,000 feet). The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters (35,797 feet). The western Pacific has many peripheral seas.