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Unformatted text preview: Lecture 9 2/14/11 Heating the Terrestrial Worlds Planetary interiors heat up through: Accretion Differentiation Radioactivity Accretion and differentation supply all the heat at the beginning Radioactivity supplies heat throughout the planet's life Cooling the Terrestrial Worlds Planets cool off through: Conduction: heat flowing on the microscopic level Convection: heat flowing on the marcroscopic levels (bulk motions) eruptions: hot lava bursts through crust The larger the planet, the longer it takes to cool off! Internal heat drives convection in the solid rock mantle, w hich pushes the lithosphere around (tectonics) Origins of the Continents Seafloor crust ( and volcanoes): Basalt: high density igneous rock 5 to 10 km thick < 0.2 byr old Continental crust: Granite: lower density igneous rock 20 to 70 km thick up to 4.0 byr old floats like an iceberg Plate tectonics: Recycles seafloor crust Continually add to continental crust Plate Tectonics Wegener (1880 1930): proposed continental drift Seafloor spreading: Mantle material erupts at the mid-ocean ridges Continents move away from each other (a few cm/yr) Subduction: seafloor pushing under continental crust back into the mantle (recycling Lithosphere divides into ~ dozen plates expect plate tectonics to have been even stronger in past (more internal heat) Continents get built up over time What about other planets? A planet's fundamental properties determin its geological fate Impact craters important early on affects all planets equally Volcanism & Tectonic become dominant later on require internal heat...
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- Winter '11