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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
- Plate Tectonics, co2 cycle, density igneous rock