![]() ![]() ![]() This process reduces the total surface area (crust) of the Earth. Along convergent plate boundaries, the process of subduction, or of one plate moving under another, carries the edge of one plate down under the other plate and into the mantle. Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. The relative movement of the plates typically ranges from zero to 10 cm annually. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries (or faults). Where the plates meet, their relative motion determines the type of plate boundary: convergent, divergent, or transform. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.Įarth's lithosphere, which is the rigid outermost shell of the planet (the crust and upper mantle), is broken into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics (from the Late Latin: tectonicus, from the Ancient Greek: τεκτονικός, lit.'pertaining to building') is the scientific theory that Earth's lithosphere is comprised a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago. ![]()
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