0 Members and 1 Guest are viewing this topic.
quote:Plate tectonics (from the Greek word for "one who constructs and destroys", #964;#949;#954;#964;#969;#957;, tekton) is a theory of geology developed to explain the phenomenon of continental drift and is currently the theory accepted by the vast majority of scientists working in this area. In the theory of plate tectonics the outermost part of the Earth's interior is made up of two layers: the lithosphere comprising (1) the crust, which has an elemental composition of: oxygen, 46.6%; silicon, 27.7%; aluminum, 8.1%; and iron, 5.0%; and (2) the solidified uppermost part of the mantle. Below the lithosphere lies the asthenosphere which comprises the inner viscous part of the mantle. The mantle makes up 84% of the earth's volume and can sometimes get as hot as 3700°C. Over millions of years the mantle behaves like a superheated and extremely viscous liquid, but in response to sudden forces, such as earthquakes, it behaves like a rigid solid and can 'ring like a bell'.The lithosphere essentially "floats" on the asthenosphere. The lithosphere is broken up into what are called tectonic plates. The ten major plates are: African, Antarctic, Australian, Eurasian, North American, South American, Pacific, Cocos, Nazca, and the Indian plates. These plates (and the more numerous minor plates) move in relation to one another at one of three types of plate boundaries: convergent, divergent, and transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries (most notably around the Pacific Ring of Fire).Plate tectonic theory arose out of two separate geological observations: continental drift, noticed in the early 20th century, and seafloor spreading, noticed in the 1960s. The theory itself was developed during the late 1960s and has since almost universally been accepted by scientists and has revolutionized the earth sciences (akin in its unifying and explanatory power for diverse geological phenomena as the development of the periodic table was for chemistry, the discovery of the genetic code for biology, and quantum mechanics in physics).