2. Alfred Wegener
Proposed idea of “CONTINENTAL DRIFT”

4. Continental Drift The continents were all connected at one time
Supercontinent was called Pangea
Pangea broke apart up into two continents call Laurasia and Gondwanaland
Continents are still moving today

5. Evidence for Wegner’s Idea
Continents fit together like puzzle pieces
Fossils found on different continents were identical…how’dey do dat?
Patterns from movement of ice indicate continents were once together

7. Fossil Evidence

8. Marks from ice
movement
striations

10. No one believed Wegner…..

11. 1930
Wegener leaves for Greenland to find evidence for his hypothesis.
He is never seen again
The last photo him
His theory is hotly debated for the next 30 years

12. Continental drift meets seafloor spreading (animations from USGS)
Plate Tectonics
Continental drift meets seafloor spreading
(animations from USGS)

13. Plate Tectonics
Earth’s crust is divided into about 22 pieces called plates
Plates ‘float’ on the mantle
Convection currents in the mantle move the plates around
Movement causes earthquakes and volcanoes

14. Evidence for plate tectonics
1. Location of earthquakes and volcanoes

15. Map of earthquakes for January 2005

17. Pacific Ocean Floor:

20. The Plates

22. Evidence cont’d Age of seafloor
Oceanic igneous rock is much younger than continental igrox
Oceanic rock gets younger as you approach the mid-ocean ridge (mountain range which runs through all world’s oceans)

23. Map showing
Ages of oceanic crust

24. Magnetic pattern in rocks
Earth’s magnetic pole reverses
Magnetic crystals line up with earth’s poles when the magma hardens
Patterns in ocean rocks show parallel strips on either side of the ridge that match in width, age, distance from the ridge, and polarity

25. What pulls the lithosphere apart?

27. Heat produced by radioactive decay creates convection currents in mantle
Flow of mantle pulls lithosphere above it apart
Plates move

28. Types of Plate Boundaries
Divergent / Rift
Convergent/ Subduction
Transform

30. Divergent/ Rift
Plates move apart from one another
New basaltic crust is formed
Mid-ocean ridge: volcanic mountain range which circles the earth beneath the oceans

34. Mid-ocean ridge

35. Rift valley

37. Black
Smoker,
East Pacific Rise

38. Marie Tharp & Bruce Heezen used echo soundings to build up a picture of the ocean floor
Continent
Continent
Mid-ocean ridge
Sea mount
Central rift zone

39. trench
Mid-ocean ridge
seamounts

40. Convergent Boundary Plates collide Continental/ oceanic plates
Oceanic/ oceanic plates
Continental/ continental plates
Crust is destroyed

41. Ocean- Continent collision with subduction

42. Ocean- Continent collision with subduction

43. Andes Mountains

45. Ocean-ocean collision with subduction

46. Ocean-ocean collision with subduction

48. Hugo Benioff suggested that this Earthquake pattern show a plate subducting (sinking) into the mantle

53. Continent-continent collision (No Subduction)

54. Continent-continent collision (No Subduction)

60. 1963 Tuzo Wilson
Developed the hypothesis of hot spots to explain islands like Hawaii & a third kind of plate boundary called a transform plate boundary

61. Transform Plates slide past one another
Ex. San Andreas fault
Crust is neither created nor destroyed

63. Hot Spots Places where magma reaches earth’s surface
Not associated with plate boundary
As plate moves over hot spot, island chains form
Example: Hawaii

65. Theory of Plate tectonics
So by the mid-60’s all the evidence came together to form the
Theory of Plate tectonics
This theory states that the Earth crust is broken into a series of plates which are constantly on the move.