Plate Tectonics: History and Boundaries


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  • Evolution doesn’t work. Seeds. And cant swim
  • Plate Tectonics: History and Boundaries

    1. 1. Plate Tectonics And Plate Boundaries HORRAH!!!
    2. 2. History of Plate Tectonics and Alfred Wegener
    3. 3. History <ul><li>In the 1500’s, a Dutch mapmaker, Abraham Ortelius noticed the continents across the Atlantic Ocean fit like puzzle pieces. </li></ul><ul><li>He proposed that North and South America had been separated from Europe and Africa by earthquakes and floods . </li></ul>
    4. 4. Abraham Ortelius’ Map
    5. 5. Edward Suess <ul><li>An Austrian geologist, in the late 1800’s, proposed the southern continents had once been joined together in a single landmass </li></ul><ul><li>He named this landmass Gondwanaland. </li></ul>
    6. 6. Gondwanaland
    7. 8. Alfred Wegener <ul><li>In 1912 a German meteorologist, Alfred Wegener , had an idea about continental movement. </li></ul><ul><li>His hypothesis was called Continental Drift . </li></ul>
    8. 9. <ul><li>His hypothesis proposed that the continent’s had once been joined as a single landmass, called PANGAEA. </li></ul><ul><li>‘ Pangaea’ is a greek word meaning ‘All the Earth’ </li></ul>
    9. 10. PANGAEA <ul><li>Wegener believed that Pangaea began to break apart 250 million years ago. </li></ul><ul><li>The continents have been continuously moving since then to where they are now. </li></ul>
    10. 11. Wegener’s Evidence??? <ul><li>Use your text book and find out at least 4 of the lines of evidence Wegener used to support his theory. </li></ul><ul><li>Explain why his evidence supported his continental drift theory. </li></ul><ul><li>Hints : </li></ul><ul><ul><li>Pictures help to explain </li></ul></ul><ul><ul><li>Look at Chapter 7 </li></ul></ul>
    11. 12. Wegener’s Evidence <ul><li>1. Rocks </li></ul><ul><ul><li>Believed there should be similar rock types on opposite sides of the Atlantic </li></ul></ul><ul><ul><li>Appalachian Mtns. are similar to the Scottish Highlands </li></ul></ul><ul><ul><li>Rocks in Brazil matched those in Africa (similar age of 2.2 billion years old) </li></ul></ul>
    12. 13. More Evidence <ul><li>2. Fossils </li></ul><ul><ul><li>Animal Fossils </li></ul></ul><ul><ul><ul><li>Lystrosaurus – land reptile </li></ul></ul></ul><ul><ul><ul><li>Mesosaurus – freshwater reptile </li></ul></ul></ul><ul><ul><ul><li>Cynognathus – land reptile </li></ul></ul></ul><ul><ul><ul><li>ALL couldn’t have swam across Atlantic Ocean (salt water) </li></ul></ul></ul>
    13. 14. Fossil Evidence <ul><li>Plants </li></ul><ul><ul><li>Glossopteris </li></ul></ul><ul><ul><ul><li>Seeds – too heavy to blow across ocean </li></ul></ul></ul><ul><ul><ul><ul><li>Too fragile to float across ocean </li></ul></ul></ul></ul><ul><li>Animals </li></ul><ul><ul><li>Land animals couldn’t swim </li></ul></ul><ul><ul><li>Freshwater animals can’t swim in ocean (salt water) </li></ul></ul><ul><ul><li>Couldn’t have evolved the same way in different locations! </li></ul></ul>
    14. 15. Even More Evidence… <ul><li>3. Climate </li></ul><ul><ul><li>Coal deposits found in Antarctica </li></ul></ul><ul><ul><li>Glacier deposits found in Africa, India, Australia, and South America </li></ul></ul>
    15. 16. Science Haters <ul><li>Other scientists rejected his hypothesis because he couldn’t explain what was causing the continents to move (a.k.a. HOW?) </li></ul><ul><li>He thought rotation of the Earth but physicists said no </li></ul><ul><li>Also thought continents plowed through ocean floor but there was no evidence for that. </li></ul>
    16. 17. Arthur Holmes <ul><li>1929, a geoscientist, Holmes proposed that convection occurred in the mantle. </li></ul><ul><li>This convection could push and pull plates (continents) apart or together. </li></ul><ul><li>But NO evidence!!! </li></ul>
    17. 18. FINDING EVIDENCE The first way to map the ocean floor used Sonar. This way stunk because it didn’t accurately map the floor.
    18. 19. The then invented the Magnetometer. This could detect small changes in the magnetic field in rocks and map them.
    19. 20. Seafloor Spreading <ul><li>Mid-Atlantic Ridge </li></ul>
    20. 21. Seafloor Spreading – new ocean crust is formed at ocean ridges and destroyed at deep sea trenches.
    21. 22. Harry Hess <ul><li>Used paleomagnetism and seafloor mapping to prove convection is a source for ‘continental drift’ </li></ul>
    22. 23. Convection current/Plate motion Plate motion is thought to be caused by convection currents in the asthenosphere. Since the hotter material deep in the asthenosphere is less dense it will slowly rise, as it reaches the base of the lithosphere it begins to cool, become more dense, and will sink. Rising convection currents will move plates apart (divergent), while sinking convection currents will move plates together (convergent).
    23. 24. Plate Boundaries and Convection Currents
    24. 25. Video Website – Convection Current <ul><li> </li></ul>
    25. 26. These new maps showed the different magnetism in different layers of rock. As new crust is created the iron bearing minerals point to where the magnetic pole is at the time of creation. This is called Paleomagnetism
    26. 27. Mid-Ocean Ridge <ul><li>Isochron – line of same aged rock </li></ul>
    27. 28. Magnetic Pole Reversals <ul><li>Random reversal of Earth’s Polarity </li></ul><ul><ul><li>Average irregular 300,000 year cycles </li></ul></ul><ul><ul><li>Last one was over 780,000 years ago = overdue </li></ul></ul><ul><li>Unknown as to why </li></ul><ul><ul><li>Maybe external, maybe internal… </li></ul></ul>
    28. 29. This proved that new sea floor was being created at mid-ocean ridges. Identical magnetism on opposite sides of ridges. Thus, the plates where moving.
    29. 30. Plate Boundaries and Convection Currents
    30. 31. Types of Boundaries
    31. 32. Divergent Boundaries two plates move apart
    32. 33. Ocean/Ocean Formations- ocean ridge, fissures
    33. 34. Mid-Atlantic Ridge it is 40,000 miles long
    34. 36. Mid-Ocean Ridge – Magnetic Reversals
    35. 37. Land/land Formations – rift valley
    36. 38. Great African Rift Valley
    37. 40. Video Website - Divergent <ul><li>http://www. absorblearning .com/media/item.action?quick=12n </li></ul>
    38. 41. Convergent –two plates come together
    39. 42. Land/ocean Formations- subduction zone, trench, volcanoes, earthquakes
    40. 44. Video - Subduction <ul><li> </li></ul>
    41. 45. Mt St. Helens
    42. 48. Ring of Fire
    43. 49. Land/land Formations – Large Mountains (Orogeny)
    44. 51. Video – Convergent Mtns. <ul><li> </li></ul>
    45. 52. Himalayas
    46. 55. Ocean/ocean Formations – island arc, trench
    47. 57. Eastern Caribbean
    48. 59. Video – Convergent - Island Arc <ul><li> </li></ul>
    49. 60. Transform – the plates slide past each other, they form faults
    50. 61. Friction builds up between the plates until they snap and cause EARTHQUAKES
    51. 62. San Andreas Fault
    52. 65. Hotspot
    53. 66. Hotspots The hotspot is also known as a magma chamber, it is located in the mantle
    54. 67. The Hotspot then explodes, creating a volcano
    55. 68. The plate then moves. Notice the volcano moves with the plate, but the hotspot stays were it was
    56. 69. The Hotspot then explodes again, forming a new volcano
    57. 70. The plate moves again, starting the process over
    58. 71. Another volcano is then created forming a Volcanic Chain
    59. 72. An example of a hotspot is Hawaii