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Transcript
Chapter 8 The Dynamic Planet The Dynamic Planet Geologic time scale Earth’s structure Geologic cycle Plate tectonics Big ideas Catastrophism = young, fast Earth Uniformitarianism = old, slow Earth Geologic Time Scale Age of Earth 4.6 by Oldest rock 3.96 by Life 3.4 by K-T boundary 66.4 my = end of dinosaurs Pleistocene 1.6 my Holocene 10,000 Cosmic Year Earth formed January 1st Oldest rock Valentine’s Day February 14th Life! March 1st Cretaceous-Tertiary end of dinos evening of December 25th Humans December 31st 11:49:35 Earth’s Structure Layers of material sorted by density Core Mantle Lithosphere Earth’s Structure Core Inner core solid iron 13.5 g/cc Outer core liquid iron 10.7g/cc Mantle Lower mantle solid Upper mantle solid Asthenosphere caramel layer Earth’s Structure Lithosphere Uppermost mantle solid (confusing no?) Crust = foamy, scum that floated to top Oceanic crust 3g/cc Continental crust 2.7g/cc Earth’s magnetic field Created by spinning outer core Reverses aperiodically 9 reversals in last 4 million years Some last millions of years, some thousands Reverses full strength then decays to nothing for a few thousand years Isostacy Crust floats Higher mountains have deeper roots Oceanic crust may be 5 km thick Continental crust 30-60 km thick Rock cycle Sedimentary = made from sediment Igneous = once molten Metamorphic = heated or compressed or both Igneous rock Intrusive cools within Earth Slow cooling allows large crystals to form Granite’s crystals Extrusive cools at surface Quick cooling makes small crystals Obsidian = volcanic glass Plate tectonics Proposed by many people Alfred Wegener proposed idea of continental drift in 1912 Used geologic evidence, fossil evidence, continental margins 1960s flood of data confirmed Wegener’s idea, now called plate tectonics Plate tectonics 14’s major rigid plates moved by caramel like asthenosphere Major evidence (along with Wegener’s) Magnetic reversals along spreading centers in mid-oceanic ridge Spreading rates Ages of crust Plate tectonics Oldest crust 208 my, found off Japan All continents together 225 mya, called Pangea All were together 465 mya? Review Questions 1, 2, 3, 5, 6, 7, 9, 10, 17, 19, 20, 21, 22, 23