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lecture04 - The History of Earth and Life Lecture 4 1...

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The History of Earth and Life Lecture 4 1 Structure of the Earth Differentiated Core (radius=3471 km, density=11g/cm 3 ) iron-nickel alloy with sulfur and silica Inner Core (solid) Outer Core (liquid) Mantle (radius=2883 km, density=4.5g/cm 3 ) composition of ultramafic rock Lower, Transition Zone Asthenosphere, Uppermost Crust (radius=17 km, density=2.8g/cm 3 ) Oceanic Crust ( basalt ) Continental Crust ( granite ) Lithosphere =Uppermost Mantle + Crust Hydrosphere (mostly H 2 0) (radius=3.8km, density 1.03g/cm 3 ) Atmosphere (N 2 , O 2 ) (density 0.12*10 -8 g/cm 3 ) The Surface of the Earth (Surface of the Earth's Crust) Elevations of the earth's surface are grouped into two average levels: Higher level (Continents) Dominated by lowland plains Mountain belts limited to narrow linear belts Lower level (Ocean Basins) Much of the sea floor is quite level Average depth of the sea floor is over 2 miles Deeper trenches cover small areas Additional comments Only a few percent of the earth surface is in higher mountain ranges, deeper trenches, or in the elevations between the two general levels The transition from continent to ocean floor is the steep continental slope and continental rise
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The History of Earth and Life Lecture 4 2 Plate Tectonics The first truly global tectonic theory that unifies sea-floor spreading and continental drift How Does It Work? (Processes) Lithosphere versus Asthenosphere Mantle heat convection Sea-floor spreading and origin of ocean basins Subduction and mountain building How Do We Know? (Evidence) Paleogeographic position of continents Age of the ocean crust Biogeography and Paleobiogeography Position of major mountain ranges Recent seismic zones and active volcanic chains Why Do We Care? (Consequences) Changing geography and climate through time
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