Plate tectonics


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Plate tectonics

  1. 1. Plate Tectonics Continental Drift
  2. 2. 4-1 Continental Drift – objectives… <ul><li>Explain Wegener’s hypothesis of continental drift. </li></ul><ul><li>List evidence for Wegener’s hypothesis of continental drift. </li></ul><ul><li>Describe seafloor spreading. </li></ul>
  3. 3. Continental Drift <ul><li>Began with observations made over 400 years ago. </li></ul><ul><li>The first reliable maps were studied and it was noticed that the continents fit together like a puzzle. </li></ul>
  4. 4. Hypothesis on Continental Drift. <ul><li>The continents were once part of the same landmass – Pangea </li></ul><ul><li>Surrounding Pangea was a great ocean – Panthalassa </li></ul><ul><li>About 200 mya, Pangea began breaking apart. </li></ul><ul><li>This motion caused crumpling which led to today’s land features. </li></ul>
  5. 5. Alfred Wegener <ul><li>A german scientist. </li></ul><ul><li>Proposed his hypothesis on continental drift in 1912. </li></ul>
  6. 6. Observations led to questions… <ul><li>Were the continents once part of the same landmass? </li></ul><ul><li>If so, what caused this landmass to break apart? </li></ul><ul><li>What caused the continents to move to their present locations? </li></ul>
  7. 9. Evidence <ul><li>Coastline similarities </li></ul>
  8. 10. Evidence <ul><li>Fossils </li></ul><ul><ul><li>Mesosaurus </li></ul></ul><ul><ul><li>Cynognatyhus </li></ul></ul><ul><ul><li>Lystrosaurus </li></ul></ul><ul><ul><li>Glossopteris </li></ul></ul>
  9. 12. Geologic Evidence <ul><li>Age and types of rocks </li></ul><ul><li>Mountains </li></ul><ul><ul><li>Applachian mountains fit continuously with a band of mountains in Greenland. </li></ul></ul>
  10. 13. Climatic Evidence <ul><li>Layers of glaciers in southern Africa and South America </li></ul><ul><li>Coal deposits in the Eastern US, Europe, and Sibera </li></ul><ul><li>These climatic similarities are easy to explain if the continents were once joined. </li></ul>
  11. 14. Climatic Evidence - glaciation <ul><li>Evidence of ancient glaciation indicated that parts of southern Africa, India, Australia, and South America were covered by a large ice sheet. Arrows indicate direction of ice movement. </li></ul>
  12. 15. There was little support for Wegner’s hypothesis….until.two decades after his death…
  13. 16. Seafloor Spreading <ul><li>1947, mapping the Mid-Atlantic Ridge </li></ul><ul><ul><li>Discovered the ocean floor is much younger than continental rocks. </li></ul></ul><ul><ul><ul><li>Oceanic rocks – 150 million years old </li></ul></ul></ul><ul><ul><ul><li>Continental rocks – 4 billion years old </li></ul></ul></ul><ul><li>Harry Hess suggested a hypothesis </li></ul><ul><ul><li>Seafloor spreading </li></ul></ul><ul><ul><ul><li>Rocks in/near the rift were younger as a result of the upwelling and solidification of magma. </li></ul></ul></ul>
  14. 17. Seafloor Spreading <ul><li>Seafloor spreading provided the support Wegner needed for a mechanism for continental drift. </li></ul><ul><li>Still no proof… </li></ul>
  15. 18. Paleomagnetism <ul><li>Magnetism resulting from the cooling of magma mirrors the existing magnetism of the earth. </li></ul><ul><li>Magnetic orientations were discovered that appeared normal then reversed…normal then reversed… </li></ul><ul><li>This supported seafloor spreading…and thus further anchored Wegner’s Hypothesis. </li></ul>
  16. 19. Paleomagnetism
  17. 20. Review of 4-1… <ul><li>What observation first led to Wegner’s hypothesis of continental drift? </li></ul><ul><li>What types of evidence support Wegener’s hypothesis? </li></ul><ul><li>Describe the process of seafloor spreading. </li></ul><ul><li>Explain how scientists know that the earth’s magnetic poles have reversed themselves many times during earth’s history. </li></ul>
  18. 21. 4-2 – Plate Tectonics - objectives <ul><li>Summarize the theory of Plate Tectonics. </li></ul><ul><li>Compare the characteristic geologic activities that occur along the three types of plate boundaries. </li></ul><ul><li>Explain the possible role convection currents in plate movement. </li></ul><ul><li>Summarize the theory of suspect terranes. </li></ul>
  19. 22. A theory emerges… <ul><li>1960’s… </li></ul><ul><li>A combination of continental drift and seafloor spreading… </li></ul><ul><li>Describes continental movement but also proposes a possible explanation of why and how continents move. </li></ul>
  20. 23. The Earth’s Layers <ul><li>Two types of crust: </li></ul><ul><ul><li>Oceanic – ocean floor </li></ul></ul><ul><ul><li>Continental – dry land </li></ul></ul><ul><li>Both types of crust plus the rigid upper mantle make up the Lithosphere. </li></ul>Himilayian Crust
  21. 24. The Earth’s Layers <ul><li>Lithosphere – the thin outer layer </li></ul><ul><ul><li>Lithospheric plates </li></ul></ul><ul><li>Asthenosphere – a layer of “plastic” rock </li></ul><ul><ul><li>Denser than the lithosphere. </li></ul></ul>
  22. 25. Earth’s Layers
  23. 26. Lithospheric Plate Boundaries
  24. 27. Lithospheric Plate Boundaries <ul><li>Continent margins don’t necessarily follow plate boundaries. </li></ul><ul><li>30 plates have been identified at some speed of constant motion. </li></ul>
  25. 28. Types of Plate Boundaries
  26. 29. Divergent Boundaries <ul><li>spreading centers where two lithospheric plates move away from each other </li></ul>
  27. 30. Divergent Boundaries
  28. 31. Convergent Boundaries <ul><li>A converging boundary forms when two plates move toward each other </li></ul><ul><li>Two Types </li></ul><ul><ul><li>Collision </li></ul></ul><ul><ul><li>Subduction </li></ul></ul>
  29. 32. Convergent Boundary - Collision <ul><li>Oceanic crust – Oceanic crust </li></ul>
  30. 33. Convergent Boundary - Collision <ul><li>Oceanic crust – continental crust </li></ul>
  31. 34. Convergent Boundaries <ul><li>Continental crust – continental crust </li></ul>
  32. 37. Transform Fault Boundaries <ul><li>San Andreas fault, California </li></ul>
  33. 38. Causes of Plate Motion <ul><li>Many scientists think that the movement of the lithospheric plates is due to convection currents. </li></ul>
  34. 39. Convection Currents