lecture5 - 1 Outline for Plate Tectonics ES 1100 Fall 2015 Five Big Ideas in Science 1 2 3 4 5 Model of the atom Physics Periodic Law sorting of the

lecture5 - 1 Outline for Plate Tectonics ES 1100 Fall 2015...

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Outline for Plate Tectonics ES 1100 Fall 2015 Five Big Ideas in Science 1. Model of the atom - Physics 2. Periodic Law- sorting of the elements- Chemistry 3. Big Bang Theory – Astronomy 4. Theory of Evolution – Biology 5. Theory of Plate Tectonics - Geology Plate Tectonics A paradigm shift in the way we view how Earth works Before plate Tectonics the features of Earth’s surface were explained by the theory that Earth was shrinking Plate tectonics unifies all of geology and explains the formation and location of volcanoes, earthquakes, ocean basins, mountains, other surface features, the ages of rocks, as well as the patterns of plant and animal evolution. Theory of Plate Tectonics Earth’s lithosphere is made up of rigid plates that move with respect to one another and interact at plate boundaries. Earth’s Crust Continental Crust Crust: ~ 35 km thick. Relatively low density (lighter… 2.65 g/cm 3 ). Oceanic Crust Crust: ~ 10 km thick. higher density (heavier… 3.2 g/cm 3 ). Earth’s Interior Lithosphere (crust and uppermost mantle) ~ 100-250 km thick. - Relatively rigid. Asthenosphere (upper mantle). - Around 200 km thick. - Relative ductile (plastic-like, easily deformed). The Plate Tectonic Model Lithosphere is thin, cool, and rigid. Asthenosphere is weak, hot, and plastic. 1
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Lithosphere is broken into large fragments called ‘Plates’. Plates “float” on the asthenosphere. Plates move around and interact with each other. Isostasy Plates “float” at an elevation depending on their thickness and density. Isostasy – principle that the upper parts of Earth’s outer layers are in a state of gravitational equilibrium. The condition that exists when the buoyancy force pushing the lithosphere up equals the gravitational force pulling the lithosphere down. Also called isostatic equilibrium . The lithosphere is rigid, but when a heavy load is placed on its surface (for example when a glacier expands or when a volcano builds up its surface during an eruption), the surface bends down. The plastic asthenosphere flows out from under the bending lithosphere. Isostatic Equilibrium Continental lithosphere is modeled on the left, as a thick, dense block of oak (upper mantle) and a thick layer of light cork (continental crust). The block on the right, models ocean lithosphere, with a thinner layer of oak and a thin, denser layer of pine. The surface of the continental lithosphere “rides” higher in the water than the ocean lithosphere because the denser ocean lithosphere is less buoyant. Isostatic equilibrium is based on Archimedes Principle of Buoyancy . Buoyancy is the upward force acting on an object (like an iceberg) floating or immersed in a fluid. The object displaces a volume of water equal in mass to the object. An object (like a rock) denser than water will sink, because its mass exceeds the mass of the water it displaces.
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