An ocean (from Ωκεανός, Okeanos (Oceanus) in Greek) is a principal part of the hydrosphere: a major body of saline water that, in totality, covers about 70% of the Earth's surface (or an area of some 361 million square kilometers). Nearly half of the world's marine (oceanic) waters are over 3,000 meters (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 31 to 38 ppt.