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Ch.4, Sec.3 - The Theory of Plate Tectonics plate tectonics: the theory that explains how large pieces of the Earth’s outermost layer, called tectonic plates, move and change shapes. - a boundary is where the plates touch & there are 3 types: convergent, divergent, and transform. convergent boundary: formed by the collision of two lithospheric plates. Plate Plate - there are three types of convergent boundaries: continental-continental, continental-oceanic, & oceanic-oceanic. Ch.4, Sec.3 – The Theory of Plate Tectonics divergent boundary: the boundary between two tectonic plates that are moving away from each other. Plate Plate - mid-ocean ridges are the most common type of divergent boundary. Ch.4, Sec.3 – The Theory of Plate Tectonics Ch.4, Sec.3 - The Theory of Plate Tectonics transform boundary: the boundary between tectonic plates Plate Plate that are sliding past each other horizontally. - an excellent example of a transform boundary is the San Andreas Fault in California. Ch.4, Sec.3 - The Theory of Plate Tectonics - plate motion is caused by the different densities in the asthenosphere. - thermal energy from the interior of the Earth rises to the asthenosphere & heats rocks (they expand, become less dense, and rise to the surface). - three possible causes for tectonic plate motion are: ridge push, convection, and slab pull. (pg.110) - ridge push occurs when oceanic lithosphere slides downhill under the force of gravity. Ch.4, Sec.3 - The Theory of Plate Tectonics - slab pull occurs when oceanic lithosphere sinks and pulls the rest of the tectonic plate with it. - convection occurs when hot rock rises & cool rock sinks, causing oceanic lithosphere to move sideways & away from mid-ocean ridges. - we can measure the movement (only a couple centimeters) of the plates every year with GPS systems! Ch.4, Sec.3 - The Theory of Plate Tectonics