Crash Course Geography: Rocks and Earth's Structure

Introduction

• Earth has a solid exterior made of diverse rocks.
• Volcanoes are forming new rocks as lava hardens.
• Most rocks are ancient, altering over millions of years.
• Importance of understanding rocks and their uniqueness.

Earth's Formation and Structure

• 4.5 Billion Years Ago: Earth formed from a nebula of dust and gas.
• Structure: Spheroid shape with layered shells.
• Atmosphere: First and lightest layer.
• Crust:
  • Extremely thin and low density.
  • Two types: Continental and Oceanic.

Types of Crust

• Continental Crust:
  • Major landmasses, exposed to the atmosphere.
  • Composed of silicon and aluminum.
• Oceanic Crust:
  • Forms ocean floors.
  • Composed of iron, silicon, and magnesium.

Mantle

• Located beneath the crust.
• 2900 kilometers thick.
• Rich in iron, magnesium, and silicates.
• Changes density with depth.

Core

• Outer Core: 2400 kilometers, molten iron.
• Inner Core: Solid iron, under high pressure.
• Scientists study seismic waves to understand Earth’s interior.

Rocks and Landforms

• Different layers contribute to surface rocks and landforms.
• Example: Granite in the Himalayas.
  • Formed from volcanic activity millions of years ago.

Types of Rocks

• Igneous Rocks:
  • Formed from cooled magma.
  • Make up 90% of Earth’s crust.
  • Types: Intrusive (e.g., granite) and Extrusive (e.g., basalt).

Intrusive vs Extrusive Igneous Rocks

• Intrusive: Cools slowly, larger crystals.
• Extrusive: Cools quickly, fine-grained.

Geology of the Himalayas

• Formed by the collision of Indian and Eurasian plates.
• Process:
  • Oceanic crust of Tethys Sea subducted.
  • Creation of granite from cooled magma.

Rock Cycle

• Rocks undergo continuous transformation.
• Granite Example: Can become sedimentary (like sandstone) or metamorphic (like gneiss).

Sedimentary Rocks

• Formed from compacted sediments.
• Types include sandstone and limestone.

Metamorphic Rocks

• Formed from existing rocks under pressure/heat.
• Example: Gneiss from granite.

Conclusion

• Each rock has a unique history and transformation process.
• Next: Exploring the role of plate tectonics in shaping Earth.

Acknowledgment

• Recognition of Indigenous and Aboriginal peoples and their relationship with the land.
• Encouragement to learn about local history and Indigenous cultures.

Additional Resources

• Crash Course community and Patreon support.