1. Continental Drift

2. Evidence: Fossils

3. Evidence: Rock Sequences

4. Evidence: Glaciation

5. Evidence: Glaciation (cont’d)

6. Evidence: Rock Types/Climates
glacial till & striations (scratches on rock) = polar climate
sand dunes = desert climate
coral reefs = tropical climate

7. Evidence: Rock Types/Climates

8. Evidence: Polar Wander??

9. “Uh-Oh!”: Problems with Continental Drift….

10. …an alternate explanation?
1928: Arthur Holmes suggested fluids rise toward the crust, spread, and sink again.
1930: Wegner dies, unable to adapt Holmes’ idea to his theory.

11. Mantle/Crust Structure

12. Earth’s Structure

13. A New Hope: Sea-floor Spreading

14. Testing the model….

15. Paleomagnetic reversals….

16. The seafloor spreading model is confirmed!

17. Today’s model:

18. Boundaries: Converging

19. Boundaries: Diverging

20. Boundaries: Transform

21. So, what causes plates to move?
Convection currents: drag and move the lithospheric plates above the asthenosphere
(three sources of heat produce the convection curents):
cooling of Earth’s core
radioactivity within the mantle/crust
cooling of mantle

22. Convection Cells

23. Convection Cells

24. SUMMARY OF P.T.: The plate tectonic model suggests:
(1) continents can move across the surface of the globe
(2) patterns of volcanism can change and shift across the globe as plates and their boundaries evolve and move
(3) new oceans may grow
(4) oceans basins close and are deformed to produce mountains