Plate Tectonics

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

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. (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 4. Climate

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.

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

25. 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

26. reverse polarity: magnetic orientation pointing south

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

29. 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

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

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

34. Two Types of Crust:

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

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

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

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

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

41. Plasticity: the ability of a solid to flow

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

43. Outer Core: only true liquid zone

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

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

48. Types of Plate Boundaries

49. 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