Overview
This lecture discusses the theory of continental drift, the evidence for it, and historical alternatives to explain the movement of Earth's continents.
Pangea and Continental Drift
- Pangea was a supercontinent where all Earth's landmasses were joined together.
- The current continent positions indicate that landmasses have moved over time.
- The concept of continental drift was first proposed by Alfred Wegener.
Evidence Supporting Continental Drift
- African and South American coastlines fit together, suggesting they were once connected.
- Identical fossils, such as the land reptile Lystrosaurus, are found on widely separated continents.
- Lystrosaurus fossils in Antarctica, India, and Southern Africa indicate continents were once joined, as it couldn't cross oceans.
- Mountain ranges like the Appalachians continue into Ireland and Scandinavia, showing physical connections between continents.
- Rocks contain minerals aligned with the magnetic North at the time of their formation; changes in magnetic poles help trace continental movements.
Alternative Theories and Reception
- Before continental drift, land bridges were proposed to explain similar fossils on different continents.
- Real land bridges (e.g., Bering Land Bridge, India-Sri Lanka) existed, but others, like Brazil to South Africa, were implausible.
- The idea of large, vanished land bridges was considered unrealistic.
- Wegener's theory was initially rejected and he faced ridicule.
Continents in Motion
- Continents have moved in the past, are moving now, and will keep moving.
- Movement of continents leads to the formation of mountains, volcanoes, and other geological features.
Key Terms & Definitions
- Pangea — Ancient supercontinent where all current continents were joined.
- Continental Drift — The theory that continents move across Earth's surface over time.
- Fossil Evidence — Remains of organisms used to demonstrate past connections between continents.
- Magnetic Poles — The direction of Earth's magnetic field, recorded in rock minerals as they form.
- Land Bridge — A natural connection between landmasses that may allow species migration.
Action Items / Next Steps
- Review the evidence supporting continental drift.
- Prepare for discussion on plate tectonics in the next class.