Earth's Interior: Quick Review

Layers of the Earth

• The Earth has 3 main layers: Crust, Mantle, Core; Each with distinct composition and physical properties.
• The 3 main layers can be divided further by how they act and their properties.
• Temperature and pressure increase with depth

Crust

• Outermost, thinnest layer: 5-70\ \mathrm{km}
• Surface temperature; contains 1\% of Earth's mass; touches the atmosphere; where we live
• Composition: loose rocks and soil
• Two crust types:
  • Continental crust: dry land; granite; less dense
  • Oceanic crust: ocean floor; basalt; thinner than continental crust but more dense
• Lithosphere = crust + upper mantle; rigid; divided into tectonic plates

Mantle

• Thickest layer: 2900\ \mathrm{km} thick
• Temperature: 1600-4000^\circ\mathrm{F}
• Contains 66\% of Earth's mass
• Mostly molten rock (magma)
• Sub-layers:
  • Upper mantle (part of lithosphere)
  • Asthenosphere: solid yet flowing; allows lithosphere to move (like caramel)
  • Mesosphere / lower mantle: strong, lower mantle

Core

• Outer core: liquid iron and nickel; very hot and dense; located about 4000\ \mathrm{miles} below the surface; accounts for 33\% of Earth's mass
• Inner core: solid iron and nickel; solid due to high pressures
• Note: Inner core roughly the size of Mars (per transcript)

How do we know?

• Seismic waves from earthquakes travel through Earth and reveal interior structure
• S-waves (shear) and P-waves (compressional) behave differently in solids and liquids
• Shadow zones show where certain waves are not felt; P-waves refract at core boundary; timing and strength of waves build interior picture