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Mid-Atlantic Ridge
The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a divergent tectonic plate or constructive plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, it separates the Eurasian and North American Plates, whereas in the South Atlantic it separates the African and South American Plates. The Ridge extends from a junction with the Gakkel Ridge (Mid-Arctic Ridge) northeast of Greenland southward to the Bouvet Triple Junction in the South Atlantic. Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level. The section of the ridge that includes the island of Iceland is also known as the Reykjanes Ridge. The ridge has an average spreading rate of about 2.5 cm per year.
==Discovery==
A ridge under the Atlantic Ocean was first inferred by Matthew Fontaine Maury in 1850. The ridge was discovered during the expedition of HMS ''Challenger'' in 1872.〔Hsü, Kenneth J. (1992) ''Challenger at Sea'', Princeton, Princeton University Press, page 57〕 A team of scientists on board, led by Charles Wyville Thomson, discovered a large rise in the middle of the Atlantic while investigating the future location for a transatlantic telegraph cable.〔Redfern, R.; 2001: ''Origins, the Evolution of Continents, Oceans and Life'', University of Oklahoma Press, ISBN 1-84188-192-9, p. 26〕 The existence of such a ridge was confirmed by sonar in 1925〔Alexander Hellemans and Brian Bunch, 1989, ''Timeline of Science'', Sidgwick and Jackson, London〕 and was found to extend around the Cape of Good Hope into the Indian Ocean by the German Meteor expedition.〔(Stein, Glenn, ''A Victory in Peace: The German Atlantic Expedition 1925-27,'' June 2007 )〕
In the 1950s, mapping of the Earth’s ocean floors by Bruce Heezen, Maurice Ewing, Marie Tharp and others revealed that the Mid-Atlantic Ridge had a strange bathymetry of valleys and ridges,〔Ewing, W.M.; Dorman, H.J.; Ericson, J.N. & Heezen, B.C.; 1953: ''Exploration of the northwest Atlantic mid-ocean canyon'', Bulletin of the Geological Society of America 64, p. 865-868〕 with its central valley being seismologically active and the epicenter of many earthquakes.〔Heezen, B. C. & Tharp, M.; 1954: ''Physiographic diagram of the western North Atlantic'', Bulletin of the Geological Society of America 65, p. 1261〕〔Hill, M.N. & Laughton, A.S.; 1954: ''Seismic Observations in the Eastern Atlantic, 1952'', Proceedings of the Royal Society of London, series A, mathematical & physical sciences 222(1150), p. 348-356〕 Ewing, Heezen and Tharp discovered that the ridge is part of a 40,000-km-long essentially continuous system of mid-ocean ridges on the floors of all the Earth’s oceans.〔Edgar W. Spencer, 1977, ''Introduction to the Structure of the Earth'', 2nd edition, McGraw-Hill, Tokyo〕 The discovery of this worldwide ridge system led to the theory of seafloor spreading and general acceptance of Wegener's theory of continental drift and expansion in the modified form of plate tectonics. The ridge is central to the breakup of the hypothetical supercontinent of Pangaea that began some 180 million years ago.
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