Plates

Plate tectonics (from Greek τέκτων, tektōn \"builder\" or \"mason\") is a theory of geology which was developed to explain the observed evidence for large scale motions within the Earth's crust. more...

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The theory encompassed and superseded the older theory of continental drift from the first half of the 20th century and the concept of sea floor spreading developed during the 1960s.

The outermost part of the Earth's interior is made up of two layers: above is the lithosphere, comprising the crust and the rigid uppermost part of the mantle. Below the lithosphere lies the asthenosphere, which is a more viscous zone of the mantle. Although solid, the asthenosphere has very low shear strength and can flow like a liquid on geological time scales. The deeper mantle below the asthenosphere is more rigid again.

The lithosphere essentially floats on the asthenosphere. The lithosphere has broken up into what are called tectonic plates—in the case of Earth, there are ten major and many minor plates. These 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. The lateral movement of the plates is typically at speeds of several centimetres per year.

Synopsis on development

Plate tectonic theory is currently the theory accepted by the vast majority of scientists working in the geosciences. It arose out of and was preceded by early hypotheses associated with continental drift, and following the development of the mechanism of seafloor spreading, (for which the detection of magnetic anomalies distributed by a clear pattern of parallel stripes on the seafloor served as impressive evidence) plate tectonics quickly became a theory on the brink of scientific revolution. Simultaneous advances in early seismic imaging techniques in and around wadati-benioff zones collectively with numerous other geologic observations soon solidified plate tectonics as a theory with extraordinary explanatory and predictive power in subsequent decades (and continuing). Plate tectonics was developed during the late 1960s and has since been essentially universally accepted by scientists as predominant throughout all geoscientific disciplines. The theory has revolutionized the earth sciences because of its unifying and explanatory power for diverse geological phenomena.

Key principles

The division of the outer parts of the Earth's interior into lithospheric and asthenospheric components is based on their mechanical differences. The lithosphere is cooler and more rigid, whilst the asthenosphere is hotter and mechanically weaker. This division should not be confused with the chemical subdivision of the Earth into (from innermost to outermost) core, mantle, and crust. The lithosphere contains both crust and some mantle. A given piece of mantle may be part of the lithosphere or the asthenosphere at different times, depending on its temperature, pressure and shear strength. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which float on the fluid-like (visco-elastic solid) asthenosphere. The relative fluidity of the asthenosphere allows the tectonic plates to undergo motion in different directions.

Read more at Wikipedia.org