Layers of the Earth
Layers
 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
Crust
Mantle
0.1% - 0.5%
45%
Shell
White
1%
30%
Core 54%
How do we know this?
 Seismic waves (earthquake waves)
Yolk 69% o
Speed of earthquake waves is proportional to densities and depth of layers