AS

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

Structure of the Earth (Chemical Layers)

  • earth has 3 layers that are each chemically distinct

    1. crust
    2. mantle
    3. core

The Crust

  • abundant silicate minerals (composed of SiO4 groups)

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

  • least dense

The Mantle

  • abundant iron (Fe) + magnesium (Mg)

  • some silicate minerals (minerals composed of SiO4 groups)

  • more dense than crust, less dense than core

The Core

  • mostly iron (Fe) + nickel (Ni)

  • most dense

The Crust: Two Types (Chemical Layers)

  1. continental crust:

    1. less dense (relatively more Si)

  2. oceanic crust

    1. denser (relatively more Fe, Mg)

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

Two Systems to Organize the Layers

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

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