Plate Tectonics Notes

The Iron (Fe) Earth’s Catastrophe

  • at 2800 degrees F, iron (+nickel) melted

    • dense liquid iron (+nickel) sank to form core which cause chemical differentiation

    • chemical differentiation: lighter elements rise, denser elements sink

    • result: earth has layers

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Structure of the Earth (Chemical Layers)

  • earth has 3 layers that are each chemically distinct

    1. crust

    2. mantle

    3. core

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The Crust

  • abundant silicate minerals (composed of SiO4 groups)

  • relatively rich in potassium (K) +sodium (Na)

  • least dense

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The Mantle

  • abundant iron (Fe) + magnesium (Mg)

  • some silicate minerals (minerals composed of SiO4 groups)

  • more dense than crust, less dense than core

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The Core

  • mostly iron (Fe) + nickel (Ni)

  • most dense

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The Crust: Two Types (Chemical Layers)

  1. continental crust:

    1. less dense (relatively more Si)
  2. oceanic crust

    1. denser (relatively more Fe, Mg)

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Lithosphere and Asthenosphere (Mechanical Layers)

  • they have different mechanical behaviors
    • lithosphere: strong and brittle, cold, tends to bend or break
    • asthenosphere: weak and ductile, warm (2400 degrees F), tends to flow slowly

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Two Systems to Organize the Layers

  • chemical and mechanical layers
    • you can’t use the names interchangeably

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Mechanical Layers

  • uppermost mantle and crust (chemical layers)= lithosphere (mechanical layer)

    • brittle lithosphere moves over the ductile/plastic asthenosphere
    • -lithosphere is 30-125 miles thick
    • tectonic plates move over asthenosphere

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