1. Plate Tectonics

2. BIG Idea:
Most geologic activity occurs at the boundaries between plates.

3. I. Drifting Continents
MAIN IDEA: The shape and geology of the continents suggests that they were once joined together.

5. Continental Drift
theory proposed by Alfred Wegener (VAY guh nur) in 1912
stated that the continents were once a single landmass
the continents have moved...

7. -Pangaea (“all the earth”):
supercontinent; single landmass -Panthalassa (“all seas”): huge ancient
ocean

8. A. Evidence of Continental Drift
1. Puzzle-Piece Fit

9. 2. Rock Formations
Ages, types and layers of coastal rocks of widely separated regions matched…

10. Western Africa and Eastern Brazil
Appalachians (along eastern U.S.) fit Greenland and Europe

11. 3. Fossils

13. Mesosaurus: freshwater reptile that lived 270 million years ago
remains (fossils) found in South America and Africa
impossible for these reptiles to have crossed the Atlantic

14. 4. Climate (a) Glossopteris: fern that grew in temperate climates
places where fossils had been found were once closer to the Equator
rocks containing these fern fossils had once been joined

15. (b) Coal Deposits:
Coal forms from ancient swamp plants
Coal beds found in Antarctica indicated that this frozen land once had a tropical climate
Antarctica must have been closer to the Equator

16. (c) Glacier Deposits:
found in Africa and South America
climates are much warmer there today

18. A Rejected Notion…

19. Wegener’s Continental Drift Hypothesis was never accepted by the scientific community
He could not explain what forces could cause such massive movement
Wegener died in 1930, on expedition in Greenland, while collecting evidence to further support his theory

20. II. Seafloor Spreading
MAIN IDEA: Oceanic crust forms at ocean ridges and becomes part of the seafloor.

24. 1.Mid-Atlantic Ridge: undersea mountain range with a steep narrow valley down the center
the middle of the ocean floor is very young

26. 2. Renewal of the Ocean Floor:
seafloor spreading - floor moving away from the center
Harry Hess and Robert Dietz
3. Paleomagnetism: as magma solidifies the iron-rich minerals align with magnetic north like a compass

27. reverse polarity: magnetic orientation pointing south

28. III. Plate Boundaries
MAIN IDEA: Volcanoes, mountains, and deep-sea trenches form at the boundaries between the plates

30. Theory of Plate Tectonics
Plate Tectonics: theory that the lithosphere is made of rigid plates that ‘float’ on the asthenosphere
Tectonics: the study of the formation of Earth’s features

31. What are the inferred properties of Earth’s interior?

34. Zones of Earth
1. Crust: thin, solid outermost layer; surrounds Earth like a shell surrounds an egg.

35. Two Types of Crust:

36. Continental Crust: makes up the continents (land); thicker, less dense; granitic rock
Oceanic Crust: under the oceans; thinner, MORE dense; basaltic rock

38. 2. Moho: boundary between the crust and mantle.

39. 3. Mantle: thickest layer sits below the crust
makes up 2/3 of the Earth’s mass

40. Lithosphere (‘rocky sphere’): upper part of mantle, cool and rigid

41. Asthenosphere (‘weak sphere’): lower (‘plastic’) mantle; flows like hot tar

42. Plasticity: the ability of a solid to flow

43. 4. Core: center of the Earth; two parts:
Inner Core: ball of hot, solid metals (iron and nickel)

44. Outer Core: only true liquid zone

46. If we’ve never been there, how have we learned about the interior of Earth?

47. By studying seismic waves…
Seismic Wave: vibration that travels through the Earth; results from earthquakes or huge explosions

49. Types of Plate Boundaries

50. 1. Divergent Boundaries:
two plates that are moving AWAY from each other
as plates move apart, the asthenosphere flows up to fill the empty space

53. What forms when plates DIVERGE?

54. a. Mid-Ocean Ridges. Mid-Atlantic Ridge b. Rift Valleys:
a. Mid-Ocean Ridges Mid-Atlantic Ridge b. Rift Valleys: (1) narrow valleys in the middle of ocean ridges (2) where continents separate East African Rift Valley

56. 2. Convergent Boundaries
direct collision of one plate with another

57. Three types of converging boundaries:

58. Types of Convergent Boundaries

59. Oceanic vs. Continental
Subduction Zone: – oceanic crust moves (dives) under continental crust
forms an oceanic trench and volcanic mountain range
oceanic crust is more dense than continental, thus it dives down or subducts

62. Andes Mountain Range

63. Mount Saint Helens - Cascade
Mountain Range

64. Oceanic vs. Oceanic older, more dense oceanic crust subducts
forms trenches and arcs of volcanic islands

67. Aleutian Islands
Mariana Trench

69. Continental vs. Continental
no subduction
two continental plates collide pushing up and creating folded mountains

73. 3. Transform Boundaries
Plates slide horizontally past each other

76. IV. Causes of Plate Motions
MAIN IDEA: Convection currents in the mantle cause plate motions.

77. cool material sinks as hot material rises, due to DENSITY DIFFERENCES.