1. Continental Drift
Chapter 10
Section 1

2. Continental Puzzle Do the continents fit together perfectly?
What continents fit the best?
What other information would you look for to provide evidence that continents may have once been part of one large continent?

3. Alfred Wegener & Continental Drift
1912 proposed supercontinent
Pangaea
Continents separated and drifted apart

4. Evidence
Coastline similarities
Fossils
Rock formations
Climates

5. Coastline Similarities
Continents on either side of Atlantic ocean seem to fit together
Contours of eastern coast of South America fit along the contours of the western coast of Africa

6. Coastline Similarities

7. Fossils
Mesosaurus – reptile fossils found only in southern South America and western Africa
Glossopteris – plant fossils found in South America, southern Africa, India, Australia, and Antarctica (Southern Hemisphere)

8. Mesosaurus Fossils

9. Fossil Evidence

10. Rock Formations
Mountain ranges of eastern South America (Brazilian Highlands) and western Africa (Cape Mountains) are the same
Mountain ranges in north eastern North America (Appalachian Mts.), Greenland, Scotland and northern Europe (Caledonian Mts.) are the same

11. Rock/Geologic Formation Evidence

12. Climates
Glacial evidence in South America, Antarctica, India, Australia and Africa
When viewed separately, glacial evidence on these continents suggests that the entire earth was covered with glaciers at one time, but this is contradicted by other evidence from sedimentary rocks
When continents are placed together, like a puzzle, glacial evidence is not world-wide, which coincides with other evidence
Tropical plant fossils in Antarctica
No plants currently grow in Antarctica, so plant fossils found there indicate warmer temperatures at one time

13. Climate Evidence

14. Antarctica Fossils

15. Alfred Wegener and Continental Drift
Despite the evidence that seemed to suggest Pangaea, Wegener’s continental drift hypothesis was rejected by the scientific community
If the continents were moving apart, why wasn’t the Earth expanding?
Continents don’t plow through oceanic rock, so how can they move?
There was no evidence for the mechanism of tectonic plates or their movement

16. Evidence for the Theory of Plate Tectonics
In the mid part of the 20th Century, discoveries were made as a result of Naval technologies that enables the mapping of the sea floor
Hitler had gotten very close to the U.S. in WWII, via submarines (in the coastal waters of the eastern seaboard)
U.S. raced to learn more about the ocean floor in order to develop better submarine capabilities

17. Mid-Ocean Ridges and Rift Valleys
1947 mapping project
sonic technology enabled the mapping of the sea floor
Rift valleys and mid-ocean ridges were discovered
Rift valley – a rip, or rift, in a tectonic plate at which volcanic activity is found
Mid-ocean ridge – the mountain ranges found on either side of a rift valley, formed from magma building up on either side of a rift

18. Mid-Ocean Ridge/Sea-Floor Spreading

19. Mid-Atlantic Ridge

20. Features of Mid-Ocean Ridges

21. Paleomagnetism
Magnetometers developed during WWII to detect submarine hulls also discovered that Earth’s rock record contains magnetic reversals
Normal magnetism and reverse magnetism alternates in rocks during specific periods
Magnetic symmetry – magnetic bands (reverse and normal) are mirror images on either side of mid-ocean ridges
Suggests that magnetism of Earth changes
Metals in molten magma align with the magnetism at the time of crystallization
Igneous rocks (basalt) retain the magnetic orientation at time of formation

22. Paleomagnetism

23. Additional observations of Ocean Floors
Ages of ocean floor features increase in age as distance from the ridge increases
Sediments are thinner and younger nearer ridge
Fossils are younger nearer ridge
Rocks are younger nearer ridge
All this suggests that new oceanic crust is forming at the rift valleys

25. Tectonic Plate Boundaries

26. Earth’s Active Volcanoes

27. “Ring of Fire”
Area of high seismic and volcanic activity outlining the Pacific Ocean

28. “Ring of Fire”

29. Conservation of Energy
According to the law of conservation of energy, energy can’t be created nor destroyed.
What is the source of energy that drives volcanoes?
What energy source produces earthquakes?

30. Quick Review

31. Lithosphere
Crust and upper portion of mantle

32. Lithosphere Broken into blocks called tectonic plates
Each plate may include continental crust, oceanic crust, or both
Continental crust thicker and less dense than oceanic crust

33. Lithosphere
About 15 major tectonic plates

34. Lithosphere
Tectonic plates “float” on Asthenosphere – solid, putty-like (“plastic”) rock below lithosphere
Asthenosphere flows very slowly

35. Asthenosphere

36. Tectonic Plates Interact
The tectonic plates of Earth’s lithosphere form the pieces of a very tightly-fitting puzzle.
Since plates move over the asthenosphere, they are bound to interact with each other
Plates interact at their boundaries in 3 major ways

37. Types of tectonic plate boundaries
Divergent Plate Boundaries
Convergent Plate Boundaries
Transform Plate Boundaries

38. Types of tectonic plate boundaries

39. Divergent Plate Boundaries

40. Divergent Plate Boundaries
Boundary between tectonic plates that are diverging (moving apart)
Common features
Mid-ocean ridges
Rift valleys
Seafloor spreading
Volcanic activity
Seismic activity

41. Divergent Boundary

42. Examples Mid-Atlantic Ridge
Red Sea – separation of African and Arabian plates

43. Transform plate boundary
Boundary between plates that slide past each other
Common features
Earthquakes
Faults
Example: San Andreas Fault
Offset surface features

44. Types of Plate Boundaries

45. Transform Fault Boundary

46. Offset Surface Features

47. Offset Surface Features

48. Fault

49. Fault and Offset Features

50. Convergent plate boundary
Boundary between tectonic plates that are converging
Three types of collisions
Oceanic-continental collision
Oceanic-oceanic collisions
Continental–continental collisions

51. Oceanic-Continental Collisions
Continental crust collides with oceanic crust
Oceanic crust subducts – dives beneath the continental crust

52. Oceanic-Continental Collisions
Common features
Subduction zones – areas where one tectonic plate dives beneath another tectonic plate
Oceanic trenches – area in the ocean where oceanic plate subducts
deepest points in Earth’s oceans
Peru-Chile Trench

53. Oceanic-Continental Collisions, continued
Common features
Volcanic activity
Mountain building – volcanic mountain ranges such as Rocky Mountains
Oceanic plate re-melts and rises to the surface inland from the boundary, creating mountains
Earthquakes

54. lithosphere Volcanic mountains Subduction zone Continental crust
Ocean trench
Oceanic crust
lithosphere
asthenosphere

55. Oceanic-oceanic collisions
One plate subducts
Common features
Subduction zones
Oceanic trenches – Mariana Trench (Challenger Deep – deepest point in the Earth’s ocean)
Volcanic activity
Island arcs – Japan, Aleutian Islands, Mariana Islands (volcanic mountains)
Earthquakes

56. Subduction zone
Volcanic island arc
Ocean trench
Continental crust
Oceanic crust
Volcano
Lithosphere
Asthenosphere

57. Continental-Continental Collisions
Neither plate subducts
Common features
Mountain building
Uplifted mountain ranges – Himalayan Mountains
Earthquakes

58. Uplifted mountain range
Continental crust
Lithosphere
Asthenosphere 4

59. Himalayan Mountains