1. Continental Drift & Plate Tectonics

2. The theory of Continental Drift was proposed by Alfred Wegener (1880- 1930) a German scientist. Smoking eventually killed him!!!!

3. Wegener proposed his theory in 1915 and (like many Scientists) was ridiculed for his theory.

4. One Critic of Wegener Dr. Rollin T. Chamberlin of the University of Chicago said, "Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories."

5. By the 1960’s, however, with the exploration of the ocean floors and the development of the Theory of Plate Tectonics, almost all geologists accepted Wegener’s Theory of Continental Drift…. Too bad he was long dead by then 

7. Continental Drift Alfred Wegener’s continental drift hypothesis stated that the continents had once been joined to form a single supercontinent. Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.

8. Evidence: The Continental Puzzel Why might have Wegener thought the continents were once joined together? What happens to shorelines over time?

9. Which continents appear to have separated first? Which ocean began to form when this happened?

10. Evidence: Matching Fossils Fossil evidence for continental drift includes several fossil organisms found on different landmasses. Example: Mesosaurus fossils (freshwater animal) found on Eastern South America and Southern Africa.

12. Evidence: Rock Types & Structures Rock evidence for continental exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean. Example: Appalachian Mnts. in the USA are similar to Mnts. in the British Isles & Scandinavia.

13. Evidence: Ancient Climates Glacial deposits show that ice sheets covered large areas of the southern hemisphere. In what type of climate do these past ice sheets now belong in?

15. Rejecting Wegener Wegener could not provide an explanation of exactly what made the continents move.  He proposed a tidal influence from the Moon. New technology lead to findings which then lead to a new theory called plate tectonics by 1968. Plate tectonics provides the framework for understanding most geological processes.

17. Plate Tectonics

18. A Review The lithosphere is made of the upper mantle (above the asthenosphere) plus the crust (both continental and oceanic). The lithosphere is solid and makes up the plates. The asthenosphere is the part of the mantle that is liquid or plastic or molten. The plates (lithosphere) float or are balanced on the asthenosphere. The interactions between plates are called plate tectonics.

20. The lithospheric plates move about as fast as your fingernails grow (between 2.5 cm -5.0 cm per year). This is between 1-2 inches per year.

21. The movement of the plates is by convection currents in the asthenosphere. Warm/hot magma rises and cool magma falls.

22. Major Plates of the Earth

24. Plates interact with each other. There are three types of plate interactions. Divergent Plate Boundaries Convergent Plate Boundaries Transform Fault Boundaries

25. Divergent: Plates pull apart from each other. When the plates pull apart, new magma seeps up. Forms: rifts and new seafloors (seafloor spreading)

27. Rift from Divergent Plate Boundary

28. Great Rift Valley in Africa African Plate Arabian Plate Rift

29. Rift Valley and Seafloor Spreading

31. Transform Fault Boundary: the two plates grind past each other without generating new lithosphere. Mostly occurs on seafloors. Forms: Earthquakes

32. Our Local Fault is a Transform Fault!!!

33. The San Andreas Fault

35. Convergent Plate Boundary: the plates move toward each other. The two plates hit and deform the crust. Tends to cause volcanoes and earthquakes

36. There are three different types of convergent plate boundaries.  Oceanic-Oceanic  Continental-Continental  Oceanic-Continental

37. Oceanic-Oceanic When Oceanic crust hits Oceanic crust, one of the oceanic crusts descends (subducts) under the other which creates underwater volcanoes and trenches. Volcanic island arcs form such as the Aleutian, Mariana and Tonga Islands.

39. Tonga

40. Continental-Continental When Continental Crust hits Continental Crust, mountain ranges such as the Himalayas (Indian and Eurasian Plates) are formed.

44. Oceanic-Continental When Oceanic Crust hits Continental Crust, the Oceanic Crust (which is thinner and denser) descends or subducts under the Continental Crust. This is called subduction. This forms earthquakes, trenches, mountain ranges and volcanoes.

45. Subduction Zone

46. Off the coast of South America, the Nazca Plate (oceanic) is subducting under the South American Plate (continental). This creates the Andes Mountains. It also causes earthquakes and volcanoes in this region.

47. Andes Mountains

48. Subduction also is the cause of the Ring of Fire.

49. Why does Subduction cause Volcanoes?

50. Let’s Review!!!!!

52. Hot Spots! A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface; The Pacific plate moves over a hot spot, producing the Hawaiian Islands.

53. Hawaii

55. How do we know that Plate Tectonics is happening? Paleomagnetism is the natural magnetism found in rocks; this permanent magnetization can be used to determine the location of the magnetic poles at the time the rock became magnetized.

56. Two Types of Polarity Normal polarity—when rocks show the same magnetism as the present magnetism field Reverse polarity—when rocks show the opposite magnetism as the present magnetism field

57. Paleomagnetism Found in Lava Flow

58.  The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is strong evidence of seafloor spreading.

60. More Evidence for Plate Tectonics Scientists found a close link between deep-focus earthquakes and ocean trenches. The lack of deep earthquakes along oceanic ridges is also consistent with the Theory of Plate Tectonics.