Overview
This lecture explains the theory of continental drift, the evidence supporting it, and the work of Alfred Wegener, who proposed that continents were once joined as a supercontinent called Pangaea.
Introduction to Continental Drift
- Continents appear to fit together like puzzle pieces, notably South America and Africa.
- Alfred Wegener, a German meteorologist, noticed this and theorized that continents move.
Wegener’s Theory and Pangaea
- Wegener proposed all continents were once joined in a supercontinent named Pangaea (~250 million years ago).
- "Pangaea" means "all earth" in Greek.
- Wegener's illustration showed modern continents positioned together differently than today.
Evidence for Continental Drift
- Apparent Fit of the Continents: Coastlines of continents fit together, especially South America and Africa.
- Fossil Correlation: Identical fossils (e.g., Mesosaurus) found on widely separated continents, suggesting they were once connected.
- Rock/Mountain Correlation: Similar rocks and mountain ranges of the same age found on different continents (e.g., northeastern U.S. and northern Europe).
- Paleoclimate Data: Evidence of past climates (glacial scratches in tropics, coal in cold regions) indicates continents have moved to their current locations.
Wegener’s Legacy and Limitations
- Wegener published "The Origin of Continents and Oceans" laying out his theory and evidence.
- He died on an expedition before explaining the mechanism for continental movement, and before his theory was widely accepted.
Key Terms & Definitions
- Continental Drift — The theory that continents have moved over geological time to their current positions.
- Pangaea — The supercontinent that existed about 250 million years ago.
- Fossil Correlation — Matching fossils found on different continents as evidence they were once joined.
- Glacial Striations — Scratches in bedrock from moving glaciers, used as evidence for past climates.
- Paleoclimate Data — Evidence of past climates based on geologic and fossil records.
Action Items / Next Steps
- Review the four evidences for continental drift.
- Prepare for discussion or quiz on Wegener’s theory and supporting data.