1. Plate Tectonics It’s a pretty zany idea What brought it about? Geologic observations made by Wegener and first suggested in 1915 Why is it important?

2. Geographic Evidence Fossil Evidence Types of Evidence for Continental Drift

3. Evidence from Glacial DepositsEvidence from Coal Deposits

4. Magnetic Evidence Patterns of reversal are nearly mirror image The Earth’s magnetic field can be: Normal: Compass points North Reversed: Compass points South The direction of the magnetic field is recorded by rocks as they form

5. Animation From Smith and Pun Sea Floor Spreading and Sea Floor Magnetism skip

6. Whole Ocean Magnetics

7. How Plates Behave (Bean pot analogy) Smith and Pun Plate Motions Through Time

8. The Plates The plates are essentially RIGID pieces of the Earth’s crust They move due to convection of the mantle They can contain both OCEANIC and CONTINENTAL crust Passive Margin Active Margin (Plate Boundary)

9. Isostacy D=kTDepth below waterline H=(1-k)THeight above waterline k=  B /  W Fraction of block below water line H D T Thick PineThin PineThin Oak

10. Where does continental crust come from?

11. Continental Crust

12. Three Basic Types of Plate Boundaries Divergent - plates moving away from one another (Tension) Convergent - plates moving toward one another (Compression) Transform - plates moving past one another (Shear) ! Most plates include con/divergent and transform components !

13. Smith and Pun Correlating Processes and Plate Boundaries

14. Smith and Pun Sea Floor Spreading and Sea Floor Magnetization Motion at Divergent Boundaries skip

15. Formation of Oceanic Crust Pillow lavas Sheeted dikes Sediments Gabbro Peridotite (Mantle rock)

16. Life at Midocean Ridges

17. midocean RIDGES Hotter Less Dense Higher Cooler More Dense Lower Cooler More Dense Lower

18. Smith and Pun Forming a Divergent Boundary ANIMATION 20 - Plate Divergence

19. Smith and Pun Motion at Convergent Boundaries

20. Convergent Boundaries Oceanic crust is denser and “rides lower” than continental crust Expect different things to happen –Ocean-Continent Collisions –Continent Continent Collisions Trenches Mountains

21. Animations Subduction –Animation 20- Ocean-Continent –Animation 20- Continent-Continent

22. Transform Boundaries San Andreas Fault in California –Animation 20-Transform Boundaries Transform Faults in Midocean Ridges –Motion at a transform plate boundary

23. The Complex Nature of Plate Boundaries

24. Hotspots –Smith and Pun: Hotspots and Plumes

25. What drives the plates?

26. What drives the plates, really?