Ocean

An ocean (from Ancient Greek Ὠκεανὸς (Okeanos); the World Ocean of classical antiquity) is a body of saline water that composes a large part of a planet's hydrosphere. In the context of Earth, it also refers to major divisions of the planet's World Ocean, such as the Atlantic Ocean. The word "sea" is often used interchangeably with "ocean", but a sea is a body of saline water (possibly a division of the World Ocean) in a more inland location.

Earth's global ocean is the largest confirmed surface ocean on all observable planets. Approximately 71% of the planet's surface (~3.6x10⁸ km²) is covered by saline water that is customarily divided into several principal oceans and smaller seas. Because it is the principal component of Earth's hydrosphere, the world ocean is integral to all known life, forms part of the carbon cycle, and influences climate and weather patterns. The total volume is approximately 1.3 billion cubic kilometres (310 million cu mi) with an average depth of 3,790 metres (12,430 ft). It is the habitat of 230,000 species known to science, however much of the ocean's depths remain unexplored and it is estimated that over two million marine species may exist. The origin of Earth's oceans is still unknown though they are believed to have first appeared in the Hadean period and may have been the point of origin for the emergence of life.

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