Chapter 10   ii
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Chapter 10   ii Chapter 10 ii Presentation Transcript

  • Chapter 10 Section II Seafloor Spreading
    • Using sound waves, scientists discovered a system of underwater mountain ranges called the mid-ocean ridges in many oceans.
  • In the 1960s, Harry Hess suggested the theory of seafloor spreading to explain the ridges
  • 1) Hot, less dense material below Earth’s crust rises towards the surface at the mid-ocean ridges.
  • 2) Then, it flows sideways, carrying the seafloor away from the ridge.
  • 3) As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor
  •  
  • Evidence for seafloor spreading
    • Youngest rocks are located at mid-ocean ridges.
    • Reversals of Earth’s
    • magnetic field are
    • recorded by rocks
    • in strips parallel to ridges.
  • Section III – Theory of Plate Tectonics
    • Plate movements
  • 1) Earth’s crust and upper mantle are broken into sections
  • 2). The sections, called plates, move on a plasticlike layer of the mantle
  • 3) The plates and upper mantle form the lithosphere.
  • 4. The plasticlike layer below the lithosphere is called the asthenosphere
  • Plate Boundaries
    • 1. Plates moving apart – divergent boundaries
  • Movie
    • 2. Plates moving together – convergent boundaries
    • Denser plates sink under less dense plates.
    • Newly formed hot magma forced upward forms volcanic mountains.
  •  
  • Plates Collide
    • Plates crumple up to form mountain ranges
    • Earthquakes are common.
    • Plates slide past – called transform boundaries, sudden movement can cause earthquakes.
  •  
    • Convection inside Earth – The cycle of heating, rising, cooling, and sinking of material inside Earth is thought to be the force behind plate tectonics.
  • Features caused by plate tectonics
    • 1) Fault and rift valleys.
    • 2) Mountains and Volcanoes
    • Strike-slip faults – cause of earthquakes
  • Testing for plate tectonics – scientists can measure movements as little as 1 cm per year