1. Earth’s Drifting Continents

2. Earth’s Drifting Continents
Key Concepts
1. What was Alfred Wegener’s hypothesis about the continents?
2. What evidence supported Wegener’s hypothesis?
3. Why was Wegener’s hypothesis rejected by most scientists of his day?

3. Earth’s Drifting Continents

4. Continental Drift Pangaea Fossil
Key Terms
Continental Drift
Pangaea
Fossil

5. Continental Drift A hypothesis proposed by Alfred Wegener
States that the Earth once had a single landmass that broke up into large pieces, which have since drifted apart. Wegener named this continent Pangaea.
Wegener was the first to build a detailed scientific case to support this idea.
He studied land features, fossils, and evidence of climate change

6. Evidence From Land Features
When Wegener pieced together maps of Africa and South America An ancient folded mountain chain in S. Africa matches one in Argentina
Coal fields in Europe match those in North America
Coal fields with distinctive layers in Brazil match ones with identical layers in Africa

7. Evidence from Rocks
Rock formations in Africa line up with formations in South America
Rock deposits left by glaciers are similar in the different continents suggesting they were left from the same glaciers.
Deep scratches in rocks show that glaciers once covered South Africa
Many glacier deposits found in warm areas. Must have been close to poles at one time
Other rock deposits come from coral reefs, found in colder climates today, must have been closer to the equator at one time.

8. Evidence from rock formations

9. Evidence from fossils
Fossils are the remains or traces of organisms that lived long ago.
Glossopteris fossils, located in rocks 250 million years old found in S. America, Africa, Australia, India and Antarctica
Glossopteris is a fernlike plant with seeds too large and fragile to have traveled great distances. Suggests that these places must once have been closer together.
Fossils of the freshwater reptiles Mesosaurus and Lystrosaurus have been found in places separated by oceans.
Neither reptile could have swum great distances in salt water

10. Fossils
Mesosaurus
Glossopteris
Lystrosaurus

11. Evidence from Climate
As a continent moves closer to equator it becomes warmer
As a continent moves toward the poles, it becomes colder
The continents carry fossils that were formed in its previous location
Example:
Spitsbergen, an island in the Arctic Ocean, has fossils of tropical plants

12. Wegener’s Hypothesis Rejected
Wegener tried to explain how continental drift could take place.
He theorized that the continents plowed across ocean floor
He couldn’t explain the force needed to push or pull the continents
Scientists rejected his idea because he couldn’t identify the cause of continental drift

13. Pangaea

14. Wegener Hypothesis of Continental Drift