1. Intermission: Intermission: Plate Tectonics

2. National Oceanic and atmospheric Administration/National Geophysical Data Center

3. Alfred Wegener

4. Evidence: (1) Continents Fit Together

5. Evidence: (2) Rocks & Structures Match Up

8. Evidence: (3) Glacial Features

10. Evidence: (4) Fossils

11. Pangea

12. Animation Link

13. “If we are to believe Wegener’s Hypothesis, we must forget everything which has been learned in the last 70 years and start over again.” –Critic of Continental Drift in 1928

14. Harry Hess

15. Evidence: Seafloor

16. Seafloor Age

18. Seafloor Spreading

19. Earthquake Distribution

20. Volcanoes and Plate Tectonics

21. Plate Tectonics

22. Earth’s “surface” (lithosphere) is broken into plates Plates move on asthenosphere “Geology happens” where the plates interact with one another Basic Plate Tectonics

23. Crustal Properties CrustDensityCompositionThicknessAge continental ~2.8 g/cm 3 Felsic Thick: 20-70 km Old: up to 4 Byrs oceanic ~3.2 g/cm 3 Mafic Thin: 2-10 km Young: <200 Mys

24. Divergent Boundary Results in the formation of Oceanic Crust

25. Examples:

26. Transform Boundary

27. Transform Example

28. Convergent Boundary: Subduction Results in the formation & growth of Continental Crust and destruction of Oceanic Crust Melting Produces More Felsic Magma

29. Example: Pacific Northwest

30. Example: Andes Mountains

31. Convergent Boundary: Collision Results in the growth of Continental Crust

32. What Drives Plate Tectonics? Internal Heat

33. Convection Models

34. Set the “Wayback Machine” to return to the Hadean…

35. Heat Generated by Radioactive Decay Hadean Earth was much hotter! Convection was more intense

36. Rapid Convection Created “Mini” Plates that were Quickly Subducted & Destroyed

37. Subduction Creates more Felsic Volcanic Islands

38. As Plates Move - Islands “Accrete” to Form Larger Islands

39. Greenstones & Tonalites (Granites)

40. Continental Crust Forms 3.96 Billion Year Old Gneiss

41. Archean Crust Oldest Rocks Oldest Minerals

42. Continental Evolution: One Reconstruction Up to 60% by the Proterozoic