1. Plate Tectonics California Standard 3a. & b.

2. Alfred L. Wegener
Alfred Wegener was born in Germany in He proposed the idea of the continents moving about the surface of the Earth in This idea was thought foolish at the time. However, he published this idea and after he died in this idea of the continents moving about became accepted in the 1960’s as more than an idea but a theory.

3. Alfred Wegener. The father of Plate Tectonics.

4. The Driving Force Behind Seafloor Spreading
Convection, or the heating and cooling of the asthenosphere, below the lithosphere is the driving force behind the movement of the continents.
Divergent Plate Boundaries.

6. Convection Currents

8. Mid-Atlantic Ridge and seafloor spreading

9. Evidence 1. Pangaea, original landmass 2.Fossils 3.Climatic changes
4.Rock type and formation

10. 1. Pangaea
1. Wegener proposed that at one time all continents were one which he called Pangaea or “all land”.
2. That these continents drifted to their present location.
3.These continents are continuing to drift. However, he did not propose how they were drifting.

11. Rodinia the “super” continent

12. Pangaea

13. Gondwana and Laurasia second “super” continents.

15. Plate Boundaries

17. 2. Fossil Evidence
The distribution of fossils on different continents helped to support Wegener’s theory of Continental Drift. Some of these fossils were dinosaurs such as Mesosaurus, and plants such as Clossopteris.

18. Mesosaurus dinosaur fossil and artists concept of animal

19. Glossopteris fern fossils

20. Distribution of Fossils

21. Glossopteris fern

22. 3. Climatic Evidence
1. Presence of warm weather plants on islands a long distance from any warm weather continents.
2. Evidence of glaciers in Africa, India and Australia.

23. 4. Rock Clues 1. Similar rocks on different continents.
2. Same rocks in Eastern U.S. as in Europe
3. Same rocks in S. America as in Africa

24. Evidence of Plate Movement
Volcanoes/earthquakes
Paleomagnetism
Seafloor spreading

25. Plate Boundaries Subduction Zone Convergent; subduction zone
Divergent boundary

26. Transform plate Boundaries
Transform plate boundaries occur where two plates move past one another.
The San Andreas fault that is splitting California apart is just such a plate boundary.

27. San Andreas Fault

28. San Andreas fault, aerial view

29. Tectonic Forces, Uplifting

31. Continental Divergent Boundary

32. Africa’s Rift Valley

33. Convergent Plates
The collision of the sub-continent of India smashing into the Eurasian plate creating the tallest mountains chain on Earth the Himalayan mountains.

34. Indian Plate converging with Eurasian Plate over time
Today
55 million years ago
Indian Plate converging with Eurasian Plate over time

35. Tibetan Plateau

36. San Andreas Fault

37. Juan De Fuca & N American Plate

39. Volcanoes and Juan De Fuca

40. Plate Boundaries

41. Seafloor Spreading
1. Until the 1950’s scientists did not know very much about the movement of continents. They did not know that the seafloor was spreading apart at the mid-oceanic ridges.
2. In Harry Hess proposed the concept of sea floor moving or the seafloor being moved apart.

42. Glomar Challenger Drilling on the Atlantic Ocean, 1968

43. Seafloor Spreading Evidence
1. The age of the rocks further from the mid-oceanic ridges became greater.
2. Polarity of the rocks indicated that the north and south poles have changed over time, creating magnetic “stripes along the seafloor. This became known as paleomagnetism. .

45. Paleomagnetism
As molten rock solidifies and becomes solid the iron minerals align with the Earth’s magnetic flied.
The Earth’s magnetic field has changed from pointing north and south over thousands of years.

47. Magnetic Clues
The Earth’s polarity has changed over the course of millions of years.
Therefore, the North Pole has become the South Pole and the South Pole has become the North Pole.
Thus, causing the magnetic fields of magnetic rocks to change in ‘stripes’.

48. When the iron minerals point north this is called normal polarity
When the iron minerals point north this is called normal polarity. When they point south this is called reverse polarity.
This changing pattern of north and south over thousands of years is called geomagnetic reversal time scale.

49. Paleomagnetism due to seafloor spreading.

51. Continental Drift Theory and Dinosaurs

52. Age of the Dinosaurs relived.

53. San Francisco, 1906

54. George Strait