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Plate Tectonics 10.2 08 09
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Plate Tectonics 10.2 08 09

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Transcript

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