GEOL: CHAPTER Plate Tectonics: A Unifying Theory Learning Outcomes LO1: Review early ideas about continental drift LO2: Explain the evidence for continental drift LO3: Describe Earth’s magnetic field LO4: Explain paleomagnetism and polar wandering LO5: Explain magnetic reversals and seafloor spreading Learning Outcomes, cont LO6: Explain plate tectonic theory: a unifying theory LO7: Identify the three types of plate boundaries LO8: Describe hot spots and mantle plumes LO9: Explain plate movement and motion Learning Outcomes, cont LO10: Explain the driving mechanism of plate tectonics LO11: Recognize the role of plate tectonics in the distribution natural resources LO12: Recognize the role of plate tectonics in the distribution of life Continental Drift: Early Ideas • Alfred Suess, late 19th C, noted similarities on different continents of: – Plant fossils – Glaciation – Rock sequences • Gondwanaland as supercontinent Alfred Wegener • Continental drift hypothesis, 1915 • Pangaea break-up • Presented geologic, paleomagnetic, paleontologic, and climatologic evidence • Not well received • Alexander du Toit, 1937: proposed supercontinent originally at South Pole Continental Drift Evidence • Continental fit – South America and Africa • Similarity of rock sequences and mountain ranges – Appalachian Mountains and mountains in Europe/Greenland Hot Spots and Mantle Plumes • Intraplate: oceanic and continental • Mantle plume: column of magma from deep within the mantle • Hot spot: mantle plume magma breaks through the surface • Form volcanoes • Plates move over them • Island chains: Hawaiian Islands Plate Movement • • • • • Date magnetic anomalies in seafloor crust Helps determine past plate positions Works well only for oceanic crust Can also use satellite laser data Good data back to Pangaea Plate Tectonics Driving Mechanism • • Heat from Earth’s interior Thermal convection cells, two hypotheses Asthenosphere only Entire mantle • • Slab-pull: subducting colder slab pulls rest of plate down into asthenosphere Ridge-push: gravity pushes plate from higher ocean ridges to trenches Plate Tectonics and Natural Resources • Plate tectonics helps explain distribution of petroleum and minerals • Cooling magma from subduction zone can concentrate metallic ores • Copper deposits Plate Tectonics and Distribution of Life • Life distribution depends on climate • Climate depends on: – Geographical position – Geographic barriers – Prevailing winds – Ocean currents • Plate movements and hot spot volcanoes influence distributions of organisms