1. Theory of Plate Tectonics
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2. Wegener’s Continental Drift
New evidence = new ideas
Better maps = Continental Drift
1915 – Alfred Wegener
Continental Drift hypothesis
Continents had once been joined to form a single supercontinent
Pangaea = “all land”

3. Wegener’s Evidence The Continental Puzzle Matching Fossils
Shorelines of new maps suggest South America and Africa were once joined
Matching Fossils
Fossils found of organisms in S. America and Africa are identical
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4. Wegener's Evidence 3. Rock Types and Structure
The Continents exhibit same Rock types across the Atlantic Ocean
When joined back together
Appalachian Mountains are continuous with Caledonian Mountains in Scandinavia

5. Wegener’s Evidence Ancient Climates
Ancient glaciers leave gashes in rocks after they recede
We see the common gashes exhibited in
India
S. America
Africa
Australia
This suggests they were all a part of the same land mass at one point

6. Wegener Rejected Although the evidence was compelling
Wegner had no mechanism to explain how the continents drifted apart
Suggested the Moon was tearing the crust apart
Physicists quickly attacked that idea and rejected the whole lot.

7. Theory of Plate Tectonics
Theory = Constructed to
Explain
Predict
Master Phenomena
= give mechanisms to explain events
= model of reality
More evidence = better theories

8. Theory of Plate Tectonics
New Data by 1968
Study the Ocean Floor
Earth’s Magnetic Field
Earthquake activity
Volcano activity
In light of
new evidence of Earth’s makeup
Wegener’s evidence
Theory of Plate Tectonics is best natural explanation and model of how the Earth moves