Lecture on Earth's Interior and Plate Tectonics

Introduction

• Recap of geologic time and Earth's history.
• Focus on Earth's interior: chemical composition and state (solid/liquid).
• Limited knowledge about Earth's interior; more is known about the Universe.

Earth's Layers by Composition and State

Core

• Composition: Iron (heavy due to gravitational pull).
• State: Inner Core (solid), Outer Core (liquid).
• Inner Inner Core: Recently discovered to be liquid.

Mantle

• Composition: Iron, magnesium silicates.
• State: Lower Mantle (solid), Upper Mantle (broken into Asthenosphere and Lithosphere).

Crust

• Lightest silicates.
• Layers: Asthenosphere (soft solid), Lithosphere (hard, brittle).
• Analogies: Pie (Asthenosphere like filling, Lithosphere like crust), Butter (Asthenosphere as room temp butter, Lithosphere as refrigerated butter).

Plate Tectonics

Plate Boundaries

1. Divergent Plate Boundaries:

   • Plates move apart.
   • Example: Seafloor spreading.
   • Formation of new crust from magma.

2. Convergent Plate Boundaries:

   • Plates crash together.
   • Types: Continental-Continental (create mountains like Himalayas), Oceanic-Continental (subducting, create mountains like Andes).

3. Transform Plate Boundaries:

   • Plates slide past each other.
   • Example: San Andreas Fault in California.
   • Creates smaller mountain ranges.

Convection Cells and Plate Movement

• Heat rises through mantle, affecting lithosphere movement.
• Convection cells: Heat rises, moves sideways, descends, and repeats.
• Possible gravitational influence on plate movement.

Specific Geological Features and Processes

Mountain Formation

• Divergent Boundaries: Gradual, less violent (e.g., mid-ocean ridges).
• Convergent Boundaries: Violent, steep mountains (e.g., Andes, Himalayas).
• Transform Boundaries: Smaller coastal mountains (e.g., California).

California's Geological Diversity

• Mountain Ranges: Sierra Nevada (from subducting plate), Coastal Ranges, Transverse Ranges.
• Deserts: All three types present.
• Microclimates: Due to mountains, valleys, ocean currents.
• Economy: 5th largest in the world.

African and Australian Plates

• Few mountains due to being in the middle of plates.
• East African Rift: Significant mountain range due to rifting.

Endogenic and Exogenic Processes

Endogenic Processes

• Internal forces (compression, extension, rifting).
• Tectonic uplift away from plate boundaries due to pressure.
• Example: East African Rift forming mountains like Kilimanjaro.

Exogenic Processes

• External forces (weathering by water, wind, freezing, heat).
• Break down and reshape mountains.

Hot Spots

• Thin lithosphere allows magma to rise without plate boundaries.
• Example: Hawaiian Islands formed over a hot spot.
• Evidence of plate tectonic movement.

Subduction Zones

• Recycling of lithosphere.
• Process: Old rock pushed into asthenosphere, melts, becomes new magma.

Conclusion

• Earth constantly recycles materials (rock, water, carbon).
• Next lecture: Focus on rocks.