Plate tectonics (from the Greek τέκτων; tektōn, meaning "builder" or "mason") is a theory which describes the large scale motions of Earth's lithosphere. The theory builds on the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, developed in the 1960s.
The lithosphere is broken up into what are called tectonic plates. In the case of Earth, there are currently eight major and many minor plates (see list below). The lithospheric plates ride on the asthenosphere. These plates move in relation to one another at one of three types of plate boundaries: convergent, or collisional boundaries; divergent boundaries, also called spreading centers; and transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The lateral movement of the plates is typically 50–100 mm annually.[1]
Tectonic plates are able to move because the Earth's lithosphere has a higher strength and lower density than the underlying asthenosphere. Their movement is driven by heat dissipation from the mantle. Lateral density variations in the mantle result in convection, which is transferred into tectonic plate motion through some combination of frictional drag, downward suction at the subduction zones, and variations in topography and density of the crust that result in differences in gravitational forces. The relative importance of each of these factors is unclear. (Resource information:Wikpedia)
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