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Layers of the Earth
 Crust
o Very thin outer layer (5 - 35 km)
o Two kinds
 Continental crust
 Light in color and weight (granitic)
 Averages ~35 km thick
 Oceanic crust
 Dark in color and more dense (basaltic)
 Usually ~7 km thick
 Mantle
o Thickest layer (2870 km)
o Directly under the crust
o Rocky - made mostly of silicon, oxygen, iron, and magnesium (more
dense than crust)
o Has characteristics of a solid but flows like a liquid when under
pressure (“plastic like”)
 Crust/Mantle boundary sub-layers
o Lithosphere (0 - 100 km)
 Hard shell of crust and rigid upper mantle
o Asthenosphere (100 - 350 km)
 Softer “plastic-like” layer below the lithosphere
 Also in upper mantle
o Mohorovicic discontinuity
 Very distinct boundary between the crust and mantle
 Called the “Moho”
 Outer core
o Liquid layer below the mantle (2190 km)
o Made of iron and nickel
 Inner core
o Solid innermost layer (2680 km)
o Solid due to pressures from overlying layers
o Made of very dense iron and nickel
 Earth’s magnetic field is thought to be caused by the
interaction between the liquid and solid metal of the outer and
inner cores
Comparing Earth Layers
Earth Layers
Relative Thickness
Egg Layers
Relative Thickness
0.1% - 0.5%
How do we know this?
 Seismic waves (earthquake waves)
o Speed of earthquake waves is proportional to densities and depth of