The Ocean ~ Earth News

An ocean is a body of saline water that composes a large part of a planet's hydrosphere. In the context of Earth, it refers to one or all of the major divisions of the planet's World Ocean – they are, in descending order of area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans.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.

There are several acknowledged theories as to how Earth's oceans were formed over the past 4.4 billion years.Some of the most likely contributory factors to the origin of the oceans are as follows:

The cooling of the primordial Earth to the point where the outgassed volatile components were held in an atmosphere of sufficient pressure for the stabilization and retention of liquid water.
Comets, trans-Neptunian objects or water-rich meteorites (protoplanets) from the outer reaches of the main asteroid belt colliding with the Earth may have brought water to the world's oceans. Measurements of the ratio of the hydrogen isotopes deuterium and protium point to asteroids, since similar percentage impurities in carbon-rich chondrites were found to oceanic water, whereas previous measurement of the isotopes' concentrations in comets and trans-Neptunian objects correspond only slightly to water on the earth.
Biochemically through mineralization and photosynthesis.
Gradual leakage of water stored in hydrous minerals of the Earth's rocks.
Photolysis: radiation can break down chemical bonds on the surface.

Since plants require photosynthesis, life found deeper than this must either rely on material sinking from above (see marine snow) or find another energy source; hydrothermal vents are the primary option in what is known as the aphotic zone (depths exceeding 200 m). The pelagic part of the photic zone is known as the epipelagic. The pelagic part of the aphotic zone can be further divided into regions that succeed each other vertically according to temperature.

The mesopelagic is the uppermost region. Its lowermost boundary is at a thermocline of 12 °C (54 °F), which, in the tropics generally lies at 700–1,000 metres (2,300–3,300 ft). Next is the bathypelagic lying between 10 and 4 °C (50 and 39 °F), typically between 700–1,000 metres (2,300–3,300 ft) and 2,000–4,000 metres (6,600–13,000 ft) Lying along the top of the abyssal plain is the abyssalpelagic, whose lower boundary lies at about 6,000 metres (20,000 ft). The last zone includes the deep trenches, and is known as the hadalpelagic. This lies between 6,000–11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone.

The ocean has a significant effect on the biosphere. Oceanic evaporation, as a phase of the water cycle, is the source of most rainfall, and ocean temperatures determine climate and wind patterns that affect life on land. Life within the ocean evolved 3 billion years prior to life on land. Both the depth and the distance from shore strongly influence the biodiversity of the plants and animals present in each region.
Lifeforms native to the ocean include: