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  1. 1. Plate Tectonics Chapter 17 Great Idea: The entire earth is still changing, due to the slow convection of soft, hot rocks deep within the planet.
  2. 2. Chapter Outline <ul><li>The Dynamic Earth </li></ul><ul><li>Plate Tectonics: A Unifying View of Earth </li></ul><ul><li>Another Look at Volcanoes and Earthquakes </li></ul>
  3. 3. Science by the Numbers <ul><li>How long could a mountain last? </li></ul><ul><li>The case of the disappearing mountains </li></ul>
  4. 4. The Case of the Disappearing Mountains <ul><li>Erosion </li></ul><ul><ul><li>Few hundred million years </li></ul></ul><ul><ul><li>Mountains continually forming </li></ul></ul><ul><li>Earth’s surface is not static </li></ul>
  5. 5. Pike’s Peak in Colorado, US
  6. 6. Slopes and Peaks in Young and Older Mountains
  7. 7. The Dynamic Earth
  8. 8. The Dynamic Earth <ul><li>Small-scale changes </li></ul><ul><ul><li>Construction site </li></ul></ul><ul><ul><ul><li>Erosion by rain </li></ul></ul></ul><ul><li>Large-scale changes </li></ul><ul><ul><li>Volcanoes </li></ul></ul><ul><ul><li>Earthquakes </li></ul></ul><ul><ul><li>Erosion </li></ul></ul>
  9. 9. Volcanoes and Earthquakes- Evidence of Earth’s Inner Forces <ul><li>Volcano </li></ul><ul><ul><li>Magma breaks through surface </li></ul></ul><ul><li>Earthquake </li></ul><ul><ul><li>Rocks breaks along fault </li></ul></ul><ul><ul><li>Energy transmitted as wave </li></ul></ul><ul><ul><li>Richter scale </li></ul></ul>
  10. 10. Mount St. Helens – Active Volcano
  11. 11. Cross Section of a Volcano
  12. 12. Earthquake Scarp
  13. 13. Tsunami
  14. 14. The Movement of the Continents <ul><li>Francis Bacon </li></ul><ul><ul><li>Continents like a puzzle </li></ul></ul><ul><li>Alfred Wegener </li></ul><ul><ul><li>Continental Drift </li></ul></ul><ul><ul><ul><li>Continents in motion </li></ul></ul></ul>
  15. 15. Continental Atlantic Coastlines
  16. 16. The Movement of the Continents – cont. <ul><li>Current Evidence </li></ul><ul><ul><li>Ocean floors </li></ul></ul><ul><ul><li>Magnetic reversals </li></ul></ul><ul><ul><li>Rock ages </li></ul></ul>
  17. 17. Ocean Floors <ul><li>Mapping </li></ul><ul><ul><li>Ocean floor dynamic </li></ul></ul><ul><ul><ul><li>Canyons, mountains </li></ul></ul></ul><ul><ul><ul><li>Mid-Atlantic Ridge </li></ul></ul></ul><ul><ul><ul><ul><li>Earthquakes, volcanoes, lava flows </li></ul></ul></ul></ul>
  18. 18. Topographic Map of the Ocean Floor
  19. 19. Magnetic Reversals <ul><li>Earth’s magnetic field </li></ul><ul><ul><li>Changes periodically </li></ul></ul><ul><li>Magnetite </li></ul><ul><ul><li>Crystals in lava align to magnetic field </li></ul></ul><ul><li>Paleomagnetism </li></ul><ul><li>Seafloor spreading </li></ul><ul><ul><li>New rock comes to surface </li></ul></ul>
  20. 20. Parallel Magnetic Strips
  21. 21. Magnetic Strips that Parallel Ocean Ridges
  22. 22. Rock Ages <ul><li>Radioactive isotopes </li></ul><ul><ul><li>Rocks near Mid-Atlantic Ridge younger </li></ul></ul><ul><ul><li>Rocks farther away older </li></ul></ul>
  23. 23. New Support for the Theory <ul><li>Measuring motion of continents </li></ul><ul><li>Radio astronomy </li></ul><ul><ul><li>Measured arrival of radio waves </li></ul></ul><ul><ul><li>Repeated over several years </li></ul></ul><ul><li>North America and Europe </li></ul><ul><ul><li>Separating at 5 cm per year </li></ul></ul>
  24. 24. Science by the Numbers <ul><li>The age of the Atlantic Ocean </li></ul><ul><li>Pangaea </li></ul>
  25. 25. Plate Tectonics: A Unifying View of Earth
  26. 26. Plate Tectonics <ul><li>Plate tectonics </li></ul><ul><ul><li>Large-scale surface features </li></ul></ul><ul><ul><li>Related phenomena </li></ul></ul>
  27. 27. Plate Tectonics – cont. <ul><li>Tectonic plates </li></ul><ul><ul><li>Rigid, moving sheet of rock </li></ul></ul><ul><ul><li>Crust and upper mantle </li></ul></ul><ul><ul><li>Continental </li></ul></ul><ul><ul><ul><li>100 km thick </li></ul></ul></ul><ul><ul><ul><li>Lower density (granite) </li></ul></ul></ul><ul><ul><li>Oceanic </li></ul></ul><ul><ul><ul><li>8-10 km thick </li></ul></ul></ul><ul><ul><ul><li>Dense rock (basalt) </li></ul></ul></ul>
  28. 28. Plate Tectonics – cont. <ul><li>Earth’s surface </li></ul><ul><ul><li>¼ continent, ¾ water </li></ul></ul>
  29. 29. Earth’s Major Plates and Direction of Motion
  30. 30. The Convecting Mantle <ul><li>Mantle convection </li></ul><ul><ul><li>Motion driven by Earth’s interior heat energy </li></ul></ul><ul><li>Sources of energy </li></ul><ul><ul><li>Gravitational potential energy </li></ul></ul><ul><ul><li>Decay of radioactive elements </li></ul></ul>
  31. 31. The Convecting Mantle – cont. <ul><li>Movement </li></ul><ul><ul><li>Heat moves to cooler regions </li></ul></ul><ul><ul><li>Convection cells in mantle </li></ul></ul><ul><ul><li>Very slow </li></ul></ul><ul><ul><ul><li>200 million years for one cycle </li></ul></ul></ul>
  32. 32. Mantle Convection
  33. 33. Science in the Making <ul><li>Reactions in plate tectonics </li></ul><ul><li>Pioneer expedition </li></ul>
  34. 34. Plate Boundaries <ul><li>Three main boundary types </li></ul><ul><ul><li>Divergent </li></ul></ul><ul><ul><li>Convergent </li></ul></ul><ul><ul><li>Transform </li></ul></ul>
  35. 35. Divergent Boundaries <ul><li>Characteristics </li></ul><ul><ul><li>Volcanoes </li></ul></ul><ul><ul><ul><li>Chain of mountains </li></ul></ul></ul><ul><ul><li>Earthquakes </li></ul></ul>
  36. 36. Divergent Plate Boundary
  37. 37. Divergent Boundaries – cont. <ul><li>Seafloor spreading </li></ul><ul><ul><li>Plates pushed apart </li></ul></ul><ul><ul><li>Old spreading centers </li></ul></ul><ul><ul><ul><li>Located in middle of ocean </li></ul></ul></ul><ul><ul><li>New spreading centers </li></ul></ul><ul><ul><ul><li>May begin anywhere </li></ul></ul></ul>
  38. 38. Africa’s Great Rift Valley
  39. 39. Convergent Plate Boundaries <ul><li>Types </li></ul><ul><ul><li>Oceanic-oceanic </li></ul></ul><ul><ul><ul><li>Subduction zone </li></ul></ul></ul><ul><ul><ul><ul><li>Deep oceanic trench </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Island arc </li></ul></ul></ul></ul>
  40. 40. Ocean-Ocean Plate
  41. 41. Convergent Plate Boundaries- cont. <ul><ul><li>Continental-continental </li></ul></ul><ul><ul><ul><li>High, jagged mountain chain </li></ul></ul></ul>
  42. 42. Continental-Continental Plate
  43. 43. Convergent Plate Boundaries- cont. <ul><ul><li>Continental-oceanic </li></ul></ul><ul><ul><ul><li>Subduction zone </li></ul></ul></ul><ul><ul><ul><ul><li>Deep oceanic trench </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Coastal mountain range </li></ul></ul></ul></ul>
  44. 44. Ocean-Continental Plate
  45. 45. Transform Plate Boundary <ul><li>Two plates move past each other </li></ul><ul><ul><li>NOT smooth </li></ul></ul><ul><ul><li>Earthquakes as a result of movement </li></ul></ul>
  46. 46. Transform Plate Boundary
  47. 47. The Science of Life <ul><li>Upright posture </li></ul><ul><li>Contributions by Richard Leakey </li></ul>
  48. 48. The Geological History of North America <ul><li>Northeastern Canada and Greenland </li></ul><ul><ul><li>Several billion years old </li></ul></ul><ul><li>Western US </li></ul><ul><ul><li>Terranes </li></ul></ul><ul><ul><ul><li>Added to continent over time </li></ul></ul></ul><ul><li>Appalachian Mountains </li></ul><ul><ul><li>Formed 450-300 million years ago </li></ul></ul><ul><ul><li>Continental-continental convergence zone </li></ul></ul>
  49. 49. The Geological History of North America – cont. <ul><li>Rocky Mountains </li></ul><ul><ul><li>60 million years ago </li></ul></ul><ul><ul><li>Warping, folding and fracturing of continent </li></ul></ul><ul><li>The Colorado Plateau </li></ul><ul><ul><li>Gentle uplift </li></ul></ul><ul><li>The Sierra Nevada </li></ul><ul><ul><li>Molten rock pushed up sediments </li></ul></ul>
  50. 50. US Mountains
  51. 51. Another Look at Volcanoes and Earthquakes <ul><li>Plates and volcanism </li></ul><ul><ul><li>Divergent plate boundaries </li></ul></ul><ul><ul><li>Convergent plate boundaries </li></ul></ul><ul><ul><ul><li>Subduction zones </li></ul></ul></ul><ul><ul><li>Hotspots </li></ul></ul><ul><ul><ul><li>Source stationary, plates move </li></ul></ul></ul><ul><ul><ul><li>Chain of volcanoes </li></ul></ul></ul><ul><li>Earthquakes </li></ul><ul><ul><li>At plate boundaries or elsewhere </li></ul></ul>
  52. 52. Volcanoes Form Above a Subduction Zone
  53. 53. The Hawaiian Islands
  54. 54. Seismology: Exploring Earth’s Interior with Earthquakes <ul><li>Seismology </li></ul><ul><ul><li>Study of sound vibrations within earth </li></ul></ul><ul><ul><li>Used to determine earth’s inner structure </li></ul></ul><ul><li>Seismic waves </li></ul><ul><ul><li>Compressional or longitudinal </li></ul></ul><ul><ul><li>Transverse or shear waves </li></ul></ul><ul><li>Earthquake predictions </li></ul>
  55. 55. Seismic Waves Passing through Earth
  56. 56. The Ongoing Process of Science <ul><li>Seismic tomography </li></ul>
  57. 57. Technology <ul><li>The design of earthquake-resistant buildings </li></ul>