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Plate Tectonics

Plate Tectonics. A Unifying Theory. Early Theory. Contraction Theory Young earth was made up of molten rock Contracted (got smaller) as it cooled forming mountain ranges. . Early Theory. Realized that the earth was heated by the breakdown of radioactive elements

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Plate Tectonics

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  1. Plate Tectonics A Unifying Theory

  2. Early Theory • Contraction Theory • Young earth was made up of molten rock • Contracted (got smaller) as it cooled forming mountain ranges.

  3. Early Theory • Realized that the earth was heated by the breakdown of radioactive elements • Earth might be getting warmer not cooler and expanding

  4. Alfred Wegener • Wasn’t buying it! • In 1910, Started lecturing and writing about his new hypothesis

  5. The Continental Drift Hypothesis • Continents were all one supercontinent called Pangaea. • Pangaea fragmented and pieces drifted to the current location of the continents

  6. Problems with Continental Drift • Scientist could not explain what caused continents to move • Didn’t believe the evidence was conclusive

  7. Evidence for Continental Drift • Matching Coastlines • South America and Africa • Matching Geology • Similar age of rocks on the coast • Similar geologic features

  8. Evidence for Continental Drift • Fossil Evidence • Glossopteris fossils in South Africa, South America, Antarctica and India

  9. Evidence for Continental Drift • Glacial Deposits • Grooves from glacial sheet movement match up

  10. Evidence for Continental Drift • Paleomagnetism- The magnetic poles of the earth have changed over time • Igneous rocks magnetize based the location of the poles while they are cooling. (mineral grains will point to magnetic north)

  11. The Missing Piece • Paleomagnetism in the sea floor • Sea floor was made up of bands of igneous basalt with alternating polarities • Bands were symmetric across the mid-Atlantic ridge

  12. Sea Floor Spreading • Rocks on either side of the ridge were moving away from each other • New molten rock was filling the gap as the floor spread. • Older rocks are farther from the ridge and new rocks are closer

  13. How fast do the plates move?

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