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Unit 6 APES Lecture Introduction to Earth Science Geologic Time Overview • Precambrian • Paleozoic • Mesozoic • Cenozoic Questions • How many extinctions have occurred/are occuring? • Where did the oxygen come from about 2.7 bya? • During what PERIOD was the majority of coal formed? • What event proceeded the development of multi-celled organisms? Earth Compositon • Core: Intermost zone; • Made up of Nickel and Iron. • Inner Core solid; • Outer Core Liquid • Mantle--molten rock or magma--circulates by convection currents. • Asthenosphere: Outer part of mantle—semi molten— ductile • Lithosphere: Brittle, outermost layer. Includes the crust. Theory of Plate Tectonics • Plate Tectonics--Earth’s Lithosphere is divided into plates, most of which in constant motion-• This is called the tectonic cycle--build up and break down lithosphere... • Oceanic plates-primarily oceans • Continental plates-primarily land masses Type of Plate Contact • Divergent Plate Boundaries: Fig aoceanic plates move apart.--sea floor spreading. • Convergent Plate Boundaries. Plates move towards each other. Oceanic plates heavier metal--iron crust... Plate Contact 2 • Collision of two continental plates--The Himalayan Mountain Range was formed by the collision between two continental plates... • Transform faults-c--plates slide sideways. Plate Tectonics 2 • Movement driven by convection cells • Seafloor spreading • Subduction--the heavier oceanic plate slides underneath the lighter continental plate San Andreas Fault Consequences of Movement • As volcanos move over geologic hot spots, can form volcanoes. • Hawaiian Islands... Questions • What kind of plate boundary formed the Rocky Mountains? • What type of boudary would be the San Andres Fault? • What type of boundary is formed by the Himalyas? • What is an oceanic trench? The Himalayas Convection and Earth Layers Rock Cycle