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Origins
Physical properties The area of the World Ocean is 361 million square kilometers (139 million sq mi), its volume is over 1,340 million cubic kilometers (319 million cu mi), and its average depth is 3,711 meters (12,175 ft). Nearly half of the world's marine waters are over 3,000 meters (9,800 ft) deep . The vast abyssal plains of the deep ocean cover about 40% of the Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea. The total mass of the hydrosphere is about 1.4 × 1021 kilograms, which is about 0.023% of the Earth's total mass. Exploration Travel on the surface of the ocean through the use of boats dates back to prehistoric times, but only in modern times has extensive underwater travel become possible. The deepest point in the ocean is the Marianas Trench located in the Pacific Ocean near the Northern Mariana Islands. It has a maximum depth of 10,923 meters (35,838 ft) . It was fully surveyed in 1951 by the British naval vessel, "Challenger II" which gave its name to the deepest part of the trench, the "Challenger Deep". Much of the bottom of the world's oceans are unexplored and unmapped. A global image of many underwater features larger than 10 kilometers (6 mi) was created in 1995 based on gravitational distortions of the nearby sea surface. Regions
Climate One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms). Ocean currents greatly affect Earth's climate by transferring warm or cold air and precipitation to coastal regions, where they may be carried inland by winds. The Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans. Ecology The oceans are home to the majority of plant and animal life on Earth. These lifeforms include: Economy The oceans are essential to transportation: most of the world's goods are moved by ship between the world's seaports. Important ship canals include the Saint Lawrence Seaway, Panama Canal, and Suez Canal. They are also an important source of valuable foodstuffs via the fishing industry. Ancient oceans Continental drift has reconfigured the Earth's oceans, joining and splitting ancient oceans to form the current oceans. Ancient oceans include: Extraterrestrial oceans Earth is the only known planet with liquid water on its surface and is certainly the only one in our own solar system. However, liquid water is thought to be present under the surface of several natural satellites, particularly the Galilean moons of Europa, and, with less certainty, Callisto and Ganymede. Geysers have been found on Enceladus. Other icy moons may have once had internal oceans that have now frozen, such as Triton. The planets Uranus and Neptune may also possess large oceans of liquid water under their thick atmospheres, though their internal structure is not well understood at this time. There is currently much debate over whether Mars once had an ocean of water in its northern hemisphere, and over what happened to it if it did; recent findings by the Mars Exploration Rover mission indicate it had some long-term standing water in at least one location, but its extent is not known. Liquid hydrocarbons were thought to be present on the surface of Titan, though it may be more accurate to describe them as "lakes" rather than an "ocean". The Cassini-Huygens space mission initially discovered only what appeared to be dry lakebeds and empty river channels, suggesting that Titan had lost what surface liquids it might have had. A more recent fly-by of Titan made by Cassini has produced radar images that strongly suggest hydrocarbon lakes near the polar regions where it is colder. Titan is also thought likely to have a subterranean water ocean under the mix of ice and hydrocarbons that forms its outer crust. Mythology The original concept of "ocean" goes back to notions of Mesopotamian and Indo-European mythology, imagining the world to be encircled by a great river, Okeanos, "Ωκεανός" in Greek, Samudra in Hindu mythology (compare also Jörmungandr, the sea serpent living in that outer ocean in Norse mythology). The world was imagined to be enclosed by a celestial ocean above the heavens, and an ocean of the underworld below (compare Rasā, Varuna). This is evidenced for example in the account of Noah's flood in Genesis 7:11, where all the fountains of the great deep were broken up, and the windows of heaven were opened (KJV), inundating the world with the waters of the celestial ocean (see also deluge (mythology)). One common misconception today is that the oceans are blue primarily because the sky is blue. In fact, water has a very slight blue colour that can only be seen in large volumes. While the sky's reflection does contribute to the blue appearance of the surface, it is not the primary cause . See also | ||||||||||||||
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