Plate Tectonic


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Plate Tectonic

  1. 1. How the theory of Continental Drift became the theory of Plate Tectonics
  2. 2. Evidence for Continental Drift <ul><li>Fossil Evidence </li></ul><ul><li>Glacier & Climate Evidence </li></ul><ul><li>Continental Fit </li></ul><ul><li>Structural & Strata Evidence </li></ul>
  3. 3. Continental Drift <ul><li>The evidence suggested that the continents were once all together in a super-continent called Pangea </li></ul><ul><li>And that the continents were not always located in the same place on the globe. </li></ul>
  4. 4. Drifting Continents <ul><li>Alfred Wegener and his supporters thought the continents were moving about the oceans like big rafts but couldn’t explain how this happened. </li></ul>
  5. 5. New Information <ul><li>After Alfred Wegener died in 1930, Continental Drift Theory was mostly disregarded. . . </li></ul><ul><li>No one knew that the key information explaining how the continents to move would lie in a remote and vast part of the world that was still almost entirely unexplored. </li></ul>
  6. 6. Secrets in the Ocean
  7. 7. Secrets in the Ocean Topography <ul><li>Most people thought the ocean floor was a flat plain except for one set of mountains. </li></ul><ul><ul><li>Laying the trans-Atlantic telegraph cable in the late 1850’s revealed there was some kind of high ridge in the mid-Atlantic </li></ul></ul><ul><ul><li>During World War II seafloor topography was mapped with sonar. </li></ul></ul>
  8. 8. Seafloor Map
  9. 9. Secrets in the Ocean Magnetism <ul><li>Magnetism in Rocks </li></ul><ul><ul><li>When lava cools, minerals get “frozen” in what ever position they were last in. </li></ul></ul><ul><ul><li>The Earths magnetic field affects some minerals so that they line up parallel to it. </li></ul></ul>
  10. 10. Measuring Magnetism <ul><li>Magnetometers were used for minesweepers in World War II. </li></ul><ul><li>By the 1950’s scientists used magnetometers to study continental and ocean rocks to study paleomagnetism . </li></ul>
  11. 11. Magnetic Polarity Time Scale <ul><li>Paleomagnetic studies showed that the Earth’s magnetic field had switched many times through geologic history </li></ul>
  12. 12. Magnetic Stripes on the Ocean Floor
  13. 13. Secrets in the Ocean Structure of the ocean floor <ul><li>Seismic studies tested the structure of the ocean crust. </li></ul>
  14. 14. Secrets in the Ocean Structure of the ocean floor <ul><li>These studies revealed that about 100 km below the hard surface, the Earth got softer. </li></ul>
  15. 15. Secrets in the Ocean Earthquakes <ul><li>Scientists found that earthquakes in the ocean were centered at the seafloor ridges. </li></ul>!science
  16. 16. Secrets in the Ocean Heat <ul><li>The flow of heat through the ocean floor was discovered to be strongest/hottest at the ridges </li></ul>
  17. 17. So what? <ul><li>None of the scientists who discovered these things thought they had anything to do with the theory of Continental Drift. </li></ul>
  18. 18. So What? <ul><li>Separately Harry Hess and Robert S. Dietz saw some of this information and had the interesting idea which they called Sea Floor Spreading. </li></ul>Harry Hess Robert S. Dietz
  19. 19. Sea Floor Spreading <ul><li>Sea Floor Spreading was the key to the new theory of Plate Tectonics. </li></ul><ul><li>Alfred Wegener’s evidence, when put together with sea floor spreading went a long way to convince people that the continents, not only could but did move apart from each other—not as huge rafts, but as passengers on tectonic plates. </li></ul>
  20. 20. Morley-Vine-Matthews Hypothesis 1966 <ul><li>Fred Vine and Drummond Matthews pulled it all together in publications in 1966 </li></ul><ul><li>Morely’s article was rejected--looking back some say that it was the most significant piece of scientific writing ever rejected from a journal. </li></ul>Lawrence Morely Fred Vine, Drummond Matthews and Dan McKenzie
  21. 21. A new theory is born <ul><li>By 1967 Sea Floor spreading was finally accepted by most geologists and the theory of Plate Tectonics was born. </li></ul>,venus,mars/earthmarsvenusindex.htm