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Divergent Boundary

Divergent Boundary

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Divergent Boundary

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  1. Divergent Boundary

  2. Mid-Ocean Ridge Spreading Center

  3. Convergent Boundary Oceanic Trench

  4. Where are the world’s earthquakes?

  5. Oceanic Trenches

  6. Spreading ridge and subduction trench form a complete convection cell

  7. “Ridge Push” “Slab Pull” What drives this system?

  8. Plate boundaries: ridges, trenches, and…?

  9. Ridges, trenches, and transform faults Transform faults are not directly related to mantle convection …necessary for doing geometry on a sphere

  10. What do these ages tell us?

  11. Hot Spot locations

  12. Absolute Plate Motion

  13. Mantle convection / Plate tectonic summary ConvectionLandformBoundary Type 1) Upwelling (hot) Mid-ocean ridge Divergent 2) Sinking (cool) Ocean trench Convergent (Subduction zone) 3) ---- Transform fault Transform 4) Hot Spot (hot) Volcanoes ---- (Concentrated upwelling)

  14. Alfred Wegener Meteorologist The Origins of Continents and Oceans 1915 “Continental drift”

  15. Modern Earth Pangaea (240 Mya)

  16. Pangaea

  17. “Utter, damned rot!” President of the prestigious American Philosophical Society “If we are to believe this hypothesis, we must forget everything we have learned in the past 70 years and start all over again” American scientist “Anyone who valued his reputation for scientific sanity would never dare support such a theory” British geologist

  18. How should we test this idea?

  19. Evidence 1: Continental Jigsaw Puzzle

  20. How far can this guy swim?

  21. Evidence 2: Fossils match across Atlantic Mesosaurus (260 Mya)

  22. Evidence 3: Rock types & structures match U.S., Africa, Greenland, British Isles, Scandinavia

  23. What do these striations result from?

  24. Would glacial striations form in an environment like this?

  25. Would glacial striations form in an environment like this?

  26. Would glacial striations form in an environment like this?

  27. Would glacial striations form in an environment like this?

  28. Evidence 4: Ancient climates

  29. The alternatives…

  30. 1950s-1960s Post-WWII Military Industrial Complex

  31. Confirmation 1: Ocean drilling

  32. Confirmation 2: Hot Spots

  33. Confirmation 3: Paleomagnetism

  34. Magnetism of seafloor matches time scale of Earth’s magnetic field

  35. Support for plate tectonic model • Continental jigsaw puzzle • Fossils match across Atlantic • Rock types/structures match across Atlantic • Ancient climates (i.e. glaciers in Africa) • Ocean drilling confirms increasing age with distance from mid-ocean ridges • Hot spots track plate movement • Paleomagnetism of lavas at ridges tracks formation of new seafloor