An ocean (from Greek Ὠκεανὸς, "okeanos" Oceanus[1]) is a major body of saline water, and a principal component of the hydrosphere. Approximately 70.9% of the Earth's surface (~3.61 x 10 8 km 2) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.
More than half of this area is over 3,000 metres (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 30 to 38 ppt. Scientists estimate that 230,000 marine life forms of all types are currently known, but the total could be up to 10 times that number.[2]
