Interior of the Earth

• Sources of Information

  • Direct Sources
    • Mining and deep drilling (e.g., Mponeng gold mine, Kola superdeep borehole)
    • Volcanic eruption and molten lava
  • Indirect Sources
    • Temperature, pressure, and density changes
    • Meteors (origin similar to Earth)
    • Gravitational anomaly
    • Magnetic field
    • Seismic waves (most important)

• Earthquakes

  • Focus (Hypocenter) and Epicentre
  • Earthquake Waves
    • Body Waves
      • P-waves (Primary/Longitudinal, fastest, travel through solid/liquid)
      • S-waves (Secondary/Transverse, travel only through solids)
    • Surface Waves (L-waves, last to arrive, most destructive)
  • Shadow Zones
    • P-wave shadow zone (105° to 145° from epicentre)
    • S-wave shadow zone (beyond 105°, proves outer core is liquid)
  • Measuring Scales
    • Richter scale (Magnitude, 0-10)
    • Mercalli scale (Intensity/Damage, I-XII)

• Structure of the Earth

  • Crust
    • Outer solid layer, brittle
    • Lithosphere (Crust + uppermost solid mantle)
    • Oceanic crust (Sima - Silica & Magnesium, denser, basaltic)
    • Continental crust (Sial - Silica & Aluminium, lighter, granitic)
  • Mantle
    • Extends from Moho's discontinuity to 2,900 km
    • Asthenosphere (Magma source, highly viscous, upper mantle)
    • Solid lower mantle
  • Core
    • Innermost layer (NiFe - Nickel & Iron)
    • Outer Core (Liquid state, generates Earth's magnetic field)
    • Inner Core (Solid state due to high pressure)

• Discontinuities of Earth's Layers

  • Conrad Discontinuity (Between upper and lower crust)
  • Mohorovicic (Moho) Discontinuity (Between crust and mantle)
  • Repetti Discontinuity (Between upper and lower mantle)
  • Gutenberg Discontinuity (Between mantle and core)
  • Lehman Discontinuity (Between outer and inner core)

• Volcanoes and Volcanic Landforms

  • Magma (underground) vs Lava (surface)
  • Types of Volcanoes
    • Shield volcanoes (basaltic, fluid, gentle slopes)
    • Composite volcanoes (explosive, viscous lava, pyroclastic material)
    • Caldera (most explosive, collapse into craters)
    • Flood basalt provinces (traps, vast sheet flows)
  • Intrusive Volcanic Landforms
    • Batholiths (large dome-shaped cooling chambers)
    • Laccoliths (mushroom-shaped, concordant)
    • Lopolith (saucer-shaped, concave)
    • Phacolith (wave-like masses in anticlines/synclines)
    • Sills (horizontal sheets)
    • Dykes (wall-like perpendicular structures)