Plate Tectonics 10.2 08 09

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Plate Tectonics 10.2 08 09

  1. 1. Ch 10 Plate Tectonics <ul><li>Section 10.2 Seafloor Spreading </li></ul>
  2. 2. After Wegener’s hypothesis of Continental Drift was rejected… <ul><li>New technology & discoveries rekindled interest in his idea </li></ul><ul><li>SONAR (Sound, Navigation and Ranging) was used to study the ocean floor in 1940’s – 1950’s </li></ul><ul><li>1947 – rocks on ocean floor found to be younger than continental rocks </li></ul>
  3. 3. Columbia University’s Vema Instrumental in discovering the Mid-Atlantic Ridge in 1950’s
  4. 4. Theory of Sea Floor Spreading <ul><li>Proposed in 1960 by Harry Hess of Princeton U. </li></ul><ul><li>if seafloor is moving, continents may also be moving </li></ul>
  5. 5. Rift zone
  6. 6. Glomar Challenger sampling ocean floor rock in 1968
  7. 7. Ages of rock get older as the distance from rift zones increases.
  8. 8. Rift zones
  9. 9. Deep sea vents found in 1976 Woods Hole Oceanographic Institute’s submarine, Alvin
  10. 13. Hydrothermal Vents
  11. 14. <ul><li>mid-1960’s – paleomagnetic reversal time scale developed for continental rock matches that of rocks found on sea floor </li></ul>Magnetic evidence for Theory of Sea Floor Spreading
  12. 15. Earth’s magnetic field has reversed many times!
  13. 17. When lava or magma solidifies, it provides us with a record of Earth’s magnetic field
  14. 18. Lava contains iron crystals which orient themselves to Earth’s magnetic field before solidifying
  15. 19. Magnetic Reversals also show that new rock forms at rift zones
  16. 20. Seafloor Spreading
  17. 21. Geomagnetic Reversal Time Scale
  18. 22. Summing up 10.2: <ul><li>Theory of Seafloor Spreading supports Wegener’s hypothesis of Continental Drift </li></ul><ul><li>Evidence from technology, repeated observations: </li></ul><ul><ul><li>Sonar – mid-ocean ridges </li></ul></ul><ul><ul><li>Drilling ocean floor – youngest rock at center </li></ul></ul><ul><ul><li>Rift zones – visible eruptions of lava </li></ul></ul><ul><ul><li>Lava rock records magnetic field – rocks on ocean floor agree with radioactive dating used for determining age of rock samples in 1940’s – 1970’s </li></ul></ul>

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