Lecture Notes: Plate Tectonics and Continental Drift

Introduction

• South America and Africa were once connected.
• Separated about 200 million years ago during Pangaea break up.
• Same plant and reptile fossils found on both continents.

Plate Tectonics Overview

• Earth's crust moves at ~10 cm/year (rate of fingernail growth).
• Movement due to plate tectonics.
• Involves Earth's mantle layers: lithosphere and asthenosphere.

Earth's Mantle Layers

• Lithosphere: Includes crust and uppermost mantle; the land around us.
• Asthenosphere: Below lithosphere, viscous but solid rock, 80-200 km below surface.

Tectonic Plates

• Lithosphere divided into tectonic plates.
• Seven primary plates plus smaller ones.
• Plates are ~100 km thick, with continental and oceanic crusts.
• Continental crust: Forms continents and shallow coastal waters.
• Oceanic crust: Forms ocean basins.
• Example: South American Plate has continental (land) and oceanic (Atlantic) crust.

Plate Movement Mechanism

• Plates float on asthenosphere, move independently.
• Movement influenced by temperature and pressure of asthenosphere.
• Theories: mantle convection, Earth's rotation, gravitational pull.
• Plates have been moving for billions of years.

Plate Boundaries and Interactions

• Divergent Boundary: Plates move apart (e.g., Mid-Atlantic Ridge).
• Convergent Boundary: Plates collide, forming mountains (e.g., Himalayas).
  • Indian Plate colliding with Eurasian Plate; Mount Everest grows 1 cm/year.
• Transform Boundary: Plates scrape past each other causing earthquakes (e.g., San Andreas Fault).

Future of Earth's Tectonics

• Plate movement will continue to reshape Earth.
• Possible future scenarios: new mountains, changing shorelines, emerging islands.
• Example: Los Angeles and San Francisco may converge.
• Speculation: South America and Africa could reunite.

Conclusion

• Continuous plate movement shapes Earth's geography.
• Movement is slow but results in significant changes over millions of years.