Jan26_09_Earth_structure_and_tectonics2

Jan26_09_Earth_structure_and_tectonics2 - Plate Tectonics...

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Plate Tectonics
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In 1965 the ideas of continental drift and seafloor spreading were integrated into the overriding concept of plate tectonics , primarily by the work of John Tuzo Wilson, a geophysicist at the University of Toronto. Main points of the Plate Tectonics theory include: Earth’s outer layer is divided into many lithospheric plates Earth’s plates float on the asthenosphere Plate movement is powered by convection currents in the asthenosphere at seafloor spreading centers, and the downward pull of a descending plate’s leading edge at subduction zones.
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A Synthesis of Continental Drift and Seafloor Spreading Produced the Theory of Plate Tectonics Where does the heat within Earth’s layers come from? Heat from within Earth keeps the asthenosphere flowing. This allows the lithosphere to keep moving. Most of the heat that drives the plates is generated by radioactive decay , given off when nuclei of unstable elements break apart. (Left) The tectonic system is powered by heat. Some parts of the mantle are warmer than others, and convection currents form when warm mantle material rises and cool material falls. Above the mantle floats the cool, rigid, lithosphere, which is fragmented into plates. Plate movement is powered by gravity: The plates slide down the ridges at the places of their formation; their dense, cool leading edges are pulled back into the mantle.
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Plate Tectonics could explain: Pattern of paleomagnetism Pattern of earthquakes and volcanic activities Pattern of sedimentation Age of continents and oceanic crust Ocean depth increases away from the mid-ocean ridge Shape of coastlines Fossil records Hot spots Atoll and guyots
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Plate tectonics : Earth’s surface consists of several major lithospheric plates. Plate tectonics theory suggests that Earth’s surface is not a static arrangement of continents and ocean, but a dynamic mosaic of jostling segments called lithospheric plates. The plates have collided, moved apart, and slipped past one another since Earth’s crust first solidified.
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Most Tectonic Activity Occurs at Plate Boundaries Seismic (i.e. earthquake) events worldwide, January 1977 through December 1986. The locations of about 10,000 earthquakes are colored red, green, and blue to represent event depths of 0-70 kilometers, 70-300 kilometers, and below 300 kilometers. Volcanic activity is also observed along the plate boundaries
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Plate Boundary Features
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Most Tectonic Activity Occurs at Plate Boundaries (Above) Plate boundaries in action. As Plate A moves to the left (west), a gap forms behind it (1) and an overlap with Plate B
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Jan26_09_Earth_structure_and_tectonics2 - Plate Tectonics...

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