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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