GEOG 203: Planet Earth

The Dynamic Planet Overview

• Course: GEOG 203: Planet Earth
• Topics Covered: Earth's Structure, The Rock Cycle, The Tectonic Cycle

Earth's Structure

• The Earth congealed from a nebula composed of dust, gas, and icy comets.
• Density sorted by gravity into concentric layers:
  • Core: heaviest
  • Crust: lightest
• Determined by: seismic shock waves

Layers of the Earth

• Core:
  • Comprises $\frac{1}{6}$ of Earth's volume, $\frac{1}{3}$ of its mass
  • Inner core: dense and solid iron
  • Outer core: molten iron; generates magnetic field protecting from solar wind and cosmic radiation
  • Temperature ranges from 3000°C to 6650°C (5400°F to 12,000°F)
• Lower and Upper Mantle:
  • Make up 80% of Earth's volume
  • May contain crystalline water structures
  • Hosts volcanic “hot spots” like Hawaii
• Lithosphere and Crust:
  • Lithosphere = upper mantle + crust
  • Crust:
  • Oceanic: about 5 km thick
  • Continental: ranges from 20–60 km thick
  • Continental crust: composed of granite (low density, $2.7 g/cm^3$)
  • Oceanic crust: composed of basalt (high density, $3.0 g/cm^3$)

The Rock Cycle

• Rocks continuously change due to internal (endogenic) processes and are worn down by external (exogenic) processes.

Types of Rocks

• Three main groups:
  • Igneous Rocks:
  • Formed by the crystallization of magma and lava
  • Intrusive igneous rocks cool slowly beneath Earth’s surface, resulting in larger crystals
  • Extrusive igneous rocks cool quickly on the surface, resulting in smaller crystals
  • Example: granite
  • Sedimentary Rocks:
  • Composed of compacted sediments derived from other rocks
  • Formed by processes such as cementation, compaction
  • Examples: sandstone, shale, limestone, coal
  • Metamorphic Rocks:
  • Formed from existing rocks that change in response to heat and pressure
  • Harder and more resistant to erosion

The Tectonic Cycle

• Involves changes in Earth's crust configuration driven by internal forces:
  • Upwelling of magma
  • Sea-floor spreading
  • Subduction
• Plate Tectonics: Earth's crust comprises 14 plates with complex movement patterns
  • Types of boundaries:
  • Divergent: plates move apart, creating new oceanic crust
  • Convergent: continental and oceanic crust collide
  • Transform: plates slide past one another

Sea-Floor Spreading

• Mechanism driving plate movement
• Occurs at mid-ocean ridges (e.g., Mid-Atlantic Ridge)
• Magnetic particles in new crust align with Earth’s magnetic field, providing a record of magnetic reversals

Subduction

• Occurs due to density differences between oceanic crust ($3 g/cm^3$) and continental crust ($2.7 g/cm^3$)
• Creates deep ocean trenches and can recycle crust as magma

Hot Spots

• Areas where hot mantle plumes create volcanic activity
• Example: The Hawaiian Islands
• As the Pacific Plate moves, islands formed by the hot spot become progressively older away from the hotspot.

Geological Time Scale

• Geological changes are often understood through the geological time scale, illustrating continental configurations and oceanic features through millions of years.

Learning Resources:

• Videos and additional content available on platforms such as YouTube.