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Transcript
Plate Tectonics SPI 0507.7.1 Describe internal forces such as volcanoes, earthquakes, faulting, and plate movements that are responsible for the earth’s major geological features such as mountains, valleys, etc Are the continents moving? Alfred Wegener was the scientist who proposed the Continental Drift Theory in the early twentieth century. Are the continents moving? Simply put, his hypothesis proposed that the continents had once been joined, and over time had drifted apart. Pangaea was a supercontinent that included all the world's landmasses in the late Paleozoic and, according to the theory of plate tectonics. Are the continents moving? What are plate tectonics? Scientists developed a theory called plate tectonics to explain how forces deep within Earth can cause the ocean floor to spread and continents to move. What are plate tectonics? This theory describes the lithosphere (the crust and upper part of the mantle) as being made of huge plate of solid rock. Earth’s continents rest on these plates. The almost- melted rock of the asthenosphere acts as a slippery surface on which the plates can move. What cause the ocean floor to move? The ocean floor between South America and Africa is spreading at a rate of 4 centimeters (1.5 inches) every year. What cause the ocean floor to move? In the middle of the ocean where the plates are moving apart, magma is pushed up from the mantle to the surface. The upward movement of magma causes tension, or a stretch or push, on the plates. This push moves the ocean floor apart and separates the plate. This is called sea floor spreading. As the hot rock reaches the surface it cools and builds up equally on both sides of the opening. The cooling rock forms the mid-ocean ridge. crust? A divergent boundary occurs when two tectonic plates move away from each other. crust? When two plates come together, it is known as a convergent boundary. crust? Two plates sliding past each other forms a transform plate boundary. http://www.classzone.com/books/earth_science/terc/content/visualizations/ es0804/es0804page01.cfm?chapter_no=08 http://www.passmyexams.co.uk/GCSE/physics/tectonic-platemotion.html#top crust? A fault is a break or crack in the rock of the lithosphere along which movement takes place. There are three types of faults. Strike-slip faults indicate rocks are sliding past each other horizontally, with little to no vertical movement. crust? Normal faults create space. Two blocks of crust pull apart, stretching the crust into a valley. crust? Reverse faults, also called thrust faults, slide one block of crust on top of another. http://www.classzone.com/books/earth_science/terc/content/ visualizations/es1103/es1103page01.cfm How are mountains created? Slow but gigantic movements of the earth’s crust form mountains. Fold mountains are formed when two plates collide head on, and their edges crumbled, much the same way as a piece of paper folds when pushed together. Example: The Himalayan Mountains were formed when India crashed into Asia and pushed up the tallest mountain range on the continents. How are mountains created? Fault block mountains form when faults or cracks in the earth's crust force some materials or blocks of rock up and others down. Instead of the earth folding over, the earth's crust fractures (pulls apart). It breaks up into blocks or chunks. Sometimes these blocks of rock move up and down, as they move apart and blocks of rock end up being stacked on one another. Example: the Sierra Nevada Mountains in North America