Earth's interior is a complex system of layers with unique properties. Seismic waves from earthquakes help us understand its structure, revealing a solid inner core, liquid outer core, and mantle beneath the crust we live on.

The Earth's magnetic field, generated by the geodynamo in the outer core, protects us from solar radiation. This field, along with plate tectonics driven by mantle convection, shapes our planet's surface and influences life on Earth.

Earth's Interior Structure and Properties

Seismic waves and Earth's interior

• Earthquakes generate seismic waves that propagate through Earth's interior
  • Compressional P-waves travel through solids and liquids (rock, magma, outer core)
  • Shear S-waves only travel through solids (rock, inner core)
• Changes in seismic wave velocities indicate variations in density and composition of Earth's layers (crust, mantle, core)
• Seismic waves refract or reflect at boundaries between different layers
  • Outer core refracts P-waves
  • Inner core reflects P-waves
  • Liquid outer core does not allow S-waves to pass through
• Seismic wave shadow zones provide evidence for Earth's core
  • P-wave shadow zone caused by refraction of waves by outer core
  • S-wave shadow zone caused by liquid outer core blocking S-waves

Composition of Earth's layers

• Core divided into solid inner core and liquid outer core
  • Composed primarily of iron and nickel
  • High density (10-13 g/cm$^3$)
  • High temperature (5000-6000 K)
• Mantle is largest layer of Earth's interior
  • Composed of iron- and magnesium-rich silicate rocks (peridotite)
  • Solid but can deform over long time scales due to high viscosity
  • Convection in mantle drives plate tectonics
• Crust is outermost layer of Earth
  • Oceanic crust is thinner (6-8 km), denser, and composed of basaltic rocks
  • Continental crust is thicker (30-50 km), less dense, and composed of granitic rocks
• The lithosphere, consisting of the crust and uppermost solid mantle, floats on the more ductile asthenosphere

Earth's magnetic field generation

• Geodynamo generates Earth's magnetic field
  1. Convection in liquid outer core creates electric currents
  2. Earth's rotation (Coriolis effect) organizes currents into magnetic field
  3. Magnetic field is self-sustaining through dynamo effect
• Earth's magnetic field approximates a dipole
  • Field lines originate near South geographic pole and terminate near North geographic pole
  • Magnetic poles do not perfectly align with geographic poles (magnetic declination)
• Magnetic field affects surrounding space
  • Deflects solar wind charged particles, creating magnetosphere
  • Traps charged particles in Van Allen radiation belts
  • Causes auroras (Northern and Southern Lights) when charged particles interact with upper atmosphere
  • Protects Earth's surface from most solar wind and cosmic rays

Plate Tectonics and Earth's Dynamic Surface

• The geosphere, encompassing all of Earth's solid components, is shaped by plate tectonic processes
• Continental drift theory proposed the movement of continents over geological time
• Seafloor spreading at mid-ocean ridges creates new oceanic crust
• Subduction zones where oceanic plates sink beneath continental plates recycle crust back into the mantle
• Convection currents in the mantle drive the movement of tectonic plates