1. Plate Tectonics

2. Continental Puzzle Alfred Wegener—continental drift
Continents had been joined to form supercontinent (PANGEA)

3. Think!

4. Continental Drift

5. Evidence
Matching Fossils
Wegener—fossils could not cross vast oceans

6. Evidence
Rock Types—matching rocks in mountain belts that are now separated by oceans

7. Evidence
Ancient Climates—glacial deposits where temperate or tropical climates today (southern Africa, South America, & India, & Australia)

8. Arguments Against Wegener
THINK! Come up with a reason why people rejected Wegener’s hypothesis Answer: no mechanism capable of moving the continents Wegener argued that Moon’s influence on tides was strong enough to move continents Also said larger, studier continents break through oceanic crust Both of these had no evidence and strong arguments against them

9. Plate Tectonics Today’s technology led to theory of plate tectonics
Provided evidence for Wegener’s continental drift hypothesis

10. Sea Floor Gave evidence for plate tectonics & continental drift
Use sonar (sound navigation & ranging)
Sound waves to calculate distance to an object

12. Deep-Ocean Trenches
Long, curved valleys along edges of ocean basins

13. Mid-Ocean Ridges
Long chain of mountains extending the length of the ocean
Rift Valley—central valley, long canyon

14. Composition of the Ocean Floor
Igneous basaltic rock
Thick layer of sediment
Sediment becomes thinner closer to ridges

15. Process of Sea-floor Spreading
Form from volcanic activity
Magma comes up and cools

16. Movement of the Ocean Floor
Average about 5cm per year
Subduction—ocean floor returns to mantle as it sinks beneath a deep ocean trench

17. Evidence for Sea-Floor Spreading
Magnetic strips—iron rich minerals become magnetized in the same direction as the existing magnetic field
Polarity & Sea-floor spreading activity break!