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Chapter 14: Plate Tectonics

Continental Drift
Seafloor Spreading
Theory of Plate Tectonics
  • The theory of Plate Tectonics came about in the 1960's with the combination of Alfred Wegener's continental drift and Harry Hess' seafloor spreading.
  • Earth Structure
    • Lithosphere - composed of the crust and upper mantle. (Think of the shell of an egg.)
    • Asthenosphere - plasticlike layer below the lithosphere. (Think of the white part of an egg.)
  • Plate Boundaries:
    • Divergent Boundaries - plates that are moving apart. They cause landforms such as rifts (ex. East Africa), mid-ocean ridges (ex. Mid-Atlantic Ridge), and ocean basins (ex. Atlantic Ocean).
    • Convergent Boundaries - plates that are coming together. These cause several different landforms depending on the types of plates that are colliding.
      • Ocean-Ocean Collision - trenches (ex. Marianas Trench)
      • Continent-Ocean Collision - volcanoes (ex. Cascade Range of Western United States)
      • Continent-Continent Collision - mountains (ex. Himalayas)
    • Transform Boundary - plates that are sliding past each other. (ex. California - San Andreas)
  • The movement in plate tectonics is due to convection in the mantle.
  • To explain convection, think of a lava lamp. It is heated up by the light underneath and becomes less dense. This causes the "lava" to rise to the top of the lamp. Once at the top, the "lava" cools, becoming more dense. It then sinks back to the bottom of the lamp where the process starts over again. In short, convection is the heating, rising, cooling and sinking of a material.
  • The next time you wait for your water to boil while you make macaroni and cheese, you can witness convection!!
(Source: Glencoe Science, Level Green, 2003.)

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