2. Continental Drift Theory

4. Continental Drift Theory
Proposed by Alfred Wegener in 1912
250 million years ago, all of the continents were combined into one super-continent called “Pangaea”
The continents gradually drifted apart to where they are today

5. “Puzzle Pieces”
Continents look like they could be part of a giant jigsaw puzzle

6. Distribution of Fossils
Plant and animal fossils found on the coastlines of different continents

7. Ancient Climates
Tropical plant remains (coal deposits) found in Antarctica
Glaciation in Africa, South America, India, and Australia during the same time

8. Sequence of Rocks
Same rock patterns found in South America, India, Africa, Antarctica and Australia

9. Problems With The Theory
Theory was not accepted by scientists…why?
Because Wegner could not identify the cause of continental drift

10. Causes of Plate Tectonics/Drifting

11. Convection Currents
Hot magma in the Earth moves toward the surface, cools, then sinks again.
Creates convection currents beneath the plates that cause the plates to move.

13. Heat Transfer The Driving Force of Plate Tectonics

14. Theory of Plate Tectonics
Plate Boundaries
Causes of Plate Tectonics

15. Plate Tectonics

16. What is Plate Tectonics
The Earth’s crust and upper mantle are broken into sections called plates
Plates move around on top of the mantle like rafts

18. What is the Lithosphere?
The crust and part of the upper mantle = lithosphere
100 km thick
Less dense than the material below it so it “floats”

19. What is the Asthenoshere?
The plastisity layer below the lithosphere = asthenosphere
The plates of the lithosphere float on the asthenosphere

21. 2 Types of Plates
Ocean plates - plates below the oceans
Continental plates - plates below the continents

22. Plate Boundaries

23. Divergent Boundaries
Boundary between two plates that are moving apart or rifting
 
RIFTING causes SEAFLOOR SPREADING

24. Divergent Boundaries create…
Mid-ocean ridges
rift valleys
fissure volcanoes

27. Convergent Boundaries
Boundaries between two plates that are colliding
 
There are 3 types…

28. Type 1 Ocean plate colliding with a less dense continental plate
Subduction Zone: where the more dense plate slides under the less dense plate
VOLCANOES occur at subduction zones

30. Andes Mountains, South America

31. Type 2 Ocean plate colliding with another ocean plate
The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH

33. Aleutian Islands, Alaska

34. Type 3 A continental plate colliding with another continental plate
Have Collision Zones:
a place where folded and thrust faulted mountains form.

37. Transform Fault Boundaries
Boundary between two plates that are sliding past each other
EARTHQUAKES along faults
Another example of a transform boundary is the San Andres Fault

39. San Andreas Fault, CA

40. Sea-Floor Spreading

41. Introduction
Tube Worms - live in the Pacific Ocean about one mile deep near the hydrothermal vents.

42. Mapping the mid-ocean ridge
The East Pacific Rise has a mid-ocean ridge.
Curves around like a baseball.
Lies hidden under hundreds of meters of water.

43. Sonar
A device that bounces sound waves off underwater objects and then records the echoes of these sound waves.
Sonar mapped mid-ocean ridges.

44. Harry Hess An American geologist who studied mid-ocean ridges.
He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.

45. At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge. As the molten material cools, it forms a strip of solid rock in the center of the ridge. Then more molten material flows into the crack.

46. Sea-floor spreading
The process that continually adds new material to the ocean floor.
Evidence molten material, magnetic stripes, and drilling samples.

47. Evidence
Magnetic Stripes. How does the pattern of matching stripes show evidence of sea-floor spreading?

48. Evidence #3 - Drilling Samples
The Glomar Challenger did a drilling sample and found rocks that the farther away from the ridge the older the rocks were. The younger ones were in the center of the ridge.