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Plate Tectonics

Plate Tectonics. The Shifting Earth. Alfred Wegener (1880-1930). German meteorologist Introduced two important ideas PANGAEA - a supercontinent which began to break up 200 MYA CONTINENTAL DRIFT - as supercontinent broke up it formed smaller continents that drifted apart.

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Plate Tectonics

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  1. Plate Tectonics The Shifting Earth

  2. Alfred Wegener (1880-1930) • German meteorologist • Introduced two important ideas • PANGAEA - a supercontinent which began to break up 200 MYA • CONTINENTAL DRIFT - as supercontinent broke up it formed smaller continents that drifted apart. • Wrote a book about his ideas in 1915 - “The Origin of Continents & Oceans”

  3. Wegener’s ideas were not well-liked.

  4. Evidence for Plate Tectonics • The Fit of the Continents

  5. Evidence for Plate Tectonics • Fossils

  6. Lystrosaurus • “Shovel lizard” - a 200-lb, 3 ft. long mammal-like reptile that had two tusks and looked like a little hippo. • Lived about 250 MYA - its remains have been found in Africa, India, Europe, Asia and Antarctica.

  7. Mesosaurus • An aquatic reptile which lived about 275 MYA. Fossil remains are found in Africa & South America. • If it could swim across the ocean it should be found everywhere... IT ISN’T!

  8. Glossopteris • The dominant tree of the southern hemisphere during the early Triassic (250 MYA). • Fossil ferns with seeds too big to blow across an ocean have been found in Africa, South America, India, Australia and Antarctica..

  9. Evidence for Plate Tectonics • MARSUPIALS - were once the dominant land animal. Were found on every continent. • Marsupials are now found only on Australia, while their descendants - like the American Opossum - can be found on other continents.

  10. Evidence for Plate Tectonics • GEOLOGICAL EVIDENCE • Rocks of different regions match. • NW Africa & Brazil • Appalachians/Newfoundland & Greenland/Northern Europe

  11. Evidence for Plate Tectonics • PALEOCLIMATIC EVIDENCE • The study of ancient climates (Wegener & his father-in-law were meteorologists) • Fossil evidence of glacial deposits of the same age in South Africa, South America, India & Australia show these countries were once over the South Pole!

  12. Evidence for Plate Tectonics • PALEOMAGNETISM • Rocks “remember” the location of magnetic poles at the time of their formation. • They indicate the LATITUDE of the rock at the time of formation. • Either the POLES WANDERED or PLATES DRIFTED.

  13. Wegener vs. the World • Some scientists called his ideas “a fairy tale” or “utter damned rot”. • Wegener was not a geologist. Scientists felt threatened by an “outsider”. • Like Darwin, he had NO MECHANISM. He couldn’t explain what drove the whole system. He knew he was right, but he couldn’t show what made it work. • It would be some 50 years before Wegener was proven correct.

  14. Mechanism of Plate Tectonics • SEA FLOOR SPREADING - mantle convection currents push magma up, which erupts at Mid-Ocean Ridges, spreading sea floor apart. • As lava is formed (basalt)it records the magnetic orientation of the Earth.

  15. Mechanism of Plate Tectonics • DIVERGENT BOUNDARY - plates move apart, resulting in upwelling of material from mantle to create new sea floor. • Result - volcanoes, volcanic activity • Examples - Mid-Ocean Ridges, Red Sea, East African Rift Valley, Mt. Kilimanjaro

  16. Mechanism of Plate Tectonics • CONVERGENT BOUNDARY - where plates move together, causing one of the slabs to be subducted (pushed under) beneath an overriding plate. • Three types: • Ocean-Continental - Subduction Zone Volcanoes. EX: Cascades, Andes • Ocean-Ocean - Volcanic Islands • Continental-Continental - Folded Mountains EX: Himalayas

  17. Mechanism of Plate Tectonics • TRANSFORM BOUNDARY - where two plates slide past each other without creating or destroying crust. • Result - Earthquakes • EX: San Andreas Fault (California)

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