1. Plate Tectonics
Continental Drift

2. Continental Drift Hypothesis
Proposed by Alfred Wegener
All continents were at one time connected
Formed supercontinent – Pangaea
Surrounded by one ocean – Panthalassa
Began breaking apart ~200 mya

3. Evidence
Similarities in coastlines

4. Evidence
Fossil remains
(Mesosaurus)

5. Evidence
Geological evidence

6. Evidence
Change in climatic patterns

7. Continental Drift Hypothesis
Rejected – no propelling force
Wegener died in 1930 in Greenland
Idea was shelved until 1960s when new evidence was introduced

8. Seafloor Spreading
Discovered while mapping Mid-Atlantic Ridge: rocks closer to ridge younger (180 million years old) than those further away (4 billion years old)

9. Harry Hess
Determined that ocean floor must be moving away from ridge; magma welling up through a rift in ridge creating new floor. Could this be propelling force?
Again, no proof!

10. Here’s the proof!!!
Paleomagnetism

11. Paleomagnetism
Iron-bearing minerals in rocks can become magnetized, solidify, and align with magnetic north (normal polarity)
Throughout history, there have been times when magnetic orientations have been to the south: magnetic reversals (reversed polarity)

12. These magnetic orientations mirror each other on either side of the ridge proving that the seafloor is spreading

13. Proof! If the ocean floor is moving, the continents are also moving.
Wegener’s proof of Continental Drift!!!