1. 2 How do we explain the geological activity of the earth? 2-1 Many pieces of information had to come together...

2. 2 Age of the Earth uniformitarianism vs catastrophism (1800’s) about 4.6 billion years old

3. 2 Continental Drift Alfred Wegener, 1912 based on Amazing fit of Africa & South America & fossils evidence

4. 2 Figure 2.2

5. 2 Figure 2.6

6. 2 Figure 2.5

7. 2 Continental Drift single super continent = Pangea –split 200 million years ago & are still drifting Wegener’s proposed mechanism = centrifugal force of spinning earth and tidal drag of moon & sun –He was WRONG about this His idea was criticized through his death in 1930

8. 2 Fig. 3-18, p. 63 Discovery of Mid-Atlantic Ridge in 1925

9. 2 Patterns of Earthquakes and Volcanoes Plotted by Wadati & Benioff in late 1930’s –Related to continental drift? –Pacific Ring of Fire a world wide pattern that followed orderly lines –many corresponded to oceanic ridges (first plotted in 1925)

10. 2 Figure 2.13a

11. 2 Youth of Ocean Floor Maximum age of ocean floor was 200 million years centers of continents were much older (3.9 billion years)

12. 2 Figure 2.12

13. 2 Mantle Studies Seismographic evidence showed that the upper mantle was deformable and plastic perhaps the continents could move

14. 2 Sea Floor Spreading 1960, Harry Hess and Robert Dietz new seafloor (basaltic crust) develops at mid-oceanic ridges and then spreads outward continental drift would be caused by the same forces

15. 2 Sea Floor Spreading powered by convection currents in the asthenosphere

16. 2 Fig. 3-11, p. 57

17. 2 Figure 2.10

18. 2 Sea Floor Spreading explained... –why ridges were hot –why ocean was deeper away from ridges –why sediments were thicker and older away from ridges

19. 2 Since the earth is not increasing in diameter...

20. 2 Fig. 3-13, p. 59

21. 2 Subduction Zones Subduction zones (Wadati-Benioff zones) were discovered where the crust plunges into the mantle crust is destroyed here explains why the ocean floor is so young

22. 2 Figure 2.20a

23. 2 Plate Tectonics 1965, primarily by Wilson lithosphere is divided into plates that float & drift on top of the plastic asthenosphere

24. 2 Figure 2.13b

25. 2 Plate Tectonics plates move about 5 cm per year Plate movement is powered by: –downward pull of descending plates leading edge –friction of asthenosphere convection currents –outward push of new seafloor at spreading centers

26. 2 Fig. 3-11, p. 57

27. 2

28. 2 Plate Tectonics plates interact at boundaries –diverge, converge or slip past each other

29. 2 Divergent Plate Boundaries spreading centers, mid-oceanic ridges a line along which two plates are moving apart new oceanic crust forms

30. 2 Figure 2.17

31. 2 Figure 2.15 Divergence along Mid-Atlantic Ridge

32. 2 Figure 2.16 Rift Valley of Iceland

33. 2 Figure 2.18a East African Rift Valley

34. 2 Fig. 3-16d, p. 61 The Red Sea = a divergent plate boundary

35. 2 Convergent Plate Boundaries aka subduction zones, Wadati-Benioff zones regions where plates are coming together crust is destroyed

36. 2 Convergent Plate Boundaries Oceanic-continent –denser oceanic crust is subducted Figure 2.20a

37. 2 Figure 2.21

38. 2 Convergent Plate Boundaries Oceanic-oceanic –older crust is more dense & is subducted –deep oceanic trenches & volcanic islands

39. 2 Convergent Plate Boundaries Continent-continent –neither plate is completely subducted –they compress & uplift forming mountains

40. 2 Figure 2.22

41. 2 Transform Plate Boundaries Plates slide laterally past each other Crust is neither created nor destroyed

42. 2 Figure 2.23

43. 2 Table 2.1

44. 2 Confirmation of Plate Tectonics Paleomagnetism –Fossil magnetic field

45. 2 Fig. 3-27, p. 69

46. 2 Fig. 3-28, p. 70 Age of the ocean floor

47. 2 Confirmation of Plate Tectonics Hot Spots –Surface expressions of plumes of magma rising from stationary heat sources in the mantle

48. 2 Fig. 3-30, p. 71

49. 2 Figure 2.25

50. 2 Figure 2.24

51. 2 Fig. 3-12, p. 58

52. 2 Figure 2.33

53. 2 Figure 2.31a

54. 2 Figure 2.31b

55. 2 Figure 2.31c

56. 2 Figure 2.31d

57. 2 Figure 2.31e

58. 2 Figure 2.31f

59. 2 Figure 2.31g

60. 2 Figure 2.31h

61. 2 Figure 2.31i

62. 2 Figure 2.31j

63. 2 Figure 2.32 What Earth may look like in 50 million years…