The Theory of Plate Tectonics


plates: a section of the lithosphere that slowly moves over the asthensophere, carrying pieces of continental crust
scientific theory: a well tested concept that explains a wide range of observations
plate tectonics: the geological theory that states that pieces of Earth's lithosphere are in constant, slow motion, driven by convection currents in the mantle
faults: breaks in Earth's crust where rocks have slipped past each other
transform boundary: the place where two plates slip past each other, moving in opposite directions
divergent boundary: the place where two plates move apart or diverge
rift valley: a deep valley caused by divergent boundaries
convergent boundaries: the place where two plates come together or converge


Theory of Plate Motion

  • canadian scientist named J. Tuzo Wilson
    • 1965 theory that cracks in the earth were actuallly the lithosphere broken into bits called plates
      • plates are in constant slow motion driven by convection currents in the mantle
        • convection current rises from mantle into the asthenosphere
        • no plate can budge without affecting the other plates surronding it

Plate Boundaries

  • faults form along plate boundaries
    • each type of boundary has different plate movement

Transform Boundaries

  • crust is neither created or destroyed at the transform boundary
    • earthquaked occur frequently along the transform boundary

Divergent Boundaries

  • mostle occur at the mid-ocean ridge
    • rift valley forms along the divergent boundary

Convergent Boundaries

  • result at this boundary is a collision or earthquake
    • collisions bring together the following: oceanic crust + oceanic crust, oceanic crust + continental crust, and continental crust + continental crust
      • oceanic crust is made mostly of basalt
      • continental crust is made mostly of granite

The Continents Slow Dance

  • plates move from about 1- 10 cm a year
  • 260 million years ago all the continents were joined together in a supercontinent called Pangaea
  • 225 million years ago the supercontinent Pangaea began to break apart

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