Tectonic plate

A tectonic plate is a piece of the Earth's crust (or lithosphere). The surface of the Earth consists of seven major tectonic plates and many more minor ones.

Related Topics:
Earth's - Crust - Lithosphere

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The plates are around 100 km (60 miles) thick and consist of two principal types of material: oceanic crust (also called sima) and continental crust (sial). Under both lies a relatively plastic layer of the Earth's mantle called the asthenosphere, which is in constant motion. This is in turn underlaid by a solid layer of mantle.

Related Topics:
Mantle - Asthenosphere

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The composition of the two types of crust differs markedly. Oceanic crust consists largely of basaltic rocks, while the continental crust consists principally of lower density granitic rocks rich in aluminium and silica. The two types of crust also differ in thickness, with continental crusts considerably thicker than oceanic.

Related Topics:
Oceanic crust - Basaltic - Continental crust - Density - Granitic - Aluminium - Silica

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The churning of the asthenosphere carries the plates along in a process known as continental drift, which is explained by the theory of plate tectonics. Interaction between the plates creates mountains and volcanoes, as well as giving rise to earthquakes and other geological phenomena.

Related Topics:
Continental drift - Plate tectonics - Mountain - Volcano - Earthquake

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The boundaries of the plates do not coincide with those of the continents. For instance, the North American Plate covers not only North America but also Greenland, far eastern Siberia and northern Japan.

Related Topics:
North American Plate - North America - Greenland - Siberia - Japan

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As far as is known, the Earth is the only planet in the Solar System to possess tectonic plates, although there have been suggestions that Mars may also have possessed plates in the past before the planet's crust froze in place.

Related Topics:
Earth - Solar System - Mars

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