1. Continental Drift

2. 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.

3. Plate Tectonics

4. Earth’s Major Plates Australian-Indian South American Pacific African
Eurasian Caribbean
Australian-Indian South American
Pacific African
Juan de Fuca Antarctic North American

5. Earth’s Major Plates

6. 2 TYPES OF CRUST 2) CONTINENTAL - less dense 1) OCEANIC - very dense
- under ocean
- thin
- very dense
2) CONTINENTAL
- less dense

7. Theory of Plate Tectonics
Movement leads to the formation of volcanoes, earthquakes, ocean trenches, mountain formations, etc.
Plates move 1-10 cm per year

8. New Technology Supports Continental Drift Theory
Earthquakes and volcanoes occur in concentrated areas.
This suggests that the crust is divided into pieces.

9. In about the late 1940’s, Sonar was invented.

10. Bats use it!

11. Sonar brought Wegner’s theory back to life!

12. Sonar made it possible for us to observe the ocean floor.

13. Soon, scientists observed a large mountain chain running down the center of the Atlantic ocean.

14. They quickly found that the ridge ran around the world!

15. Sea- floor Spreading
The longest chain of mountains in the world is the Mid-Ocean Ridge.
The mid-ocean ridge extends into all of Earth’s oceans.

16. Sea- floor Spreading
At this ridge, the molten material rises from the mantle and erupts (much like a volcano).
Molten material spreads out, pushing older rock to both sides of the ridge.

17. Sea Floor Spreading- Makes the mid ocean ridge. Animation

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

19. The further from the Mid Ocean
Ridge the rocks are, the older they are;
newer rocks in center of ridge

22. What causes the plates to move?
Convection currents in the mantle.
Scientists generally agree that convection
occurring in the mantle is the basic driving
force for plate movement.
Utube

24. Animation

29. DIVERGENT PLATE BOUNDRY
2 plates move AWAY from each other
Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys.
                                            

30. DIVERGENT PLATE BOUNDRY
2 plates move AWAY from each other
Forms volcanoes (mid-ocean ridge), cause of seafloor spreading and rift valleys.
                                            
Sea floor
spreading
Rift valley

31. If new crust is being added to Earth’s surface, is Earth getting bigger?

32. CONVERGENT PLATE BOUNDRYS
2 plates move toward each other (COLLIDING)
Three things can happen depending on what type of crust is colliding.
Oceanic to Continental (Subduction)
Continental to Continental
(Mountains Form)
3. Oceanic to Oceanic
(Subduction)
                                            

33. Continental-Continental
Crust on continents have the same density, so they push against each other forming mountains.
EX: Himalayan mountain range

34. Continental/Continental Convergence
Found- India (Mt. Everest)

35. Continental-Ocean
More dense crust of ocean is pulled beneath (subducted) the less dense continental crust.
Forms trench in ocean
Forms volcanoes on land
Subduction
zone
animation

38. What is subduction?
Subduction is the process by which the ocean floor sinks beneath the continental crust and back into the mantle.
Seen in the US on the Pacific Coast.

40. The Ring of Fire has over 400 volcanoes , both
active and dormant.
Most of the world’s earthquakes also occur
around this ‘Ring of Fire’.

41. Oceanic/Oceanic Convergence
Found- Alaska (Aleutian Islands)

44. TRANSFORM 2 plates SLIDING HORIZONTALLY past each other
Forms earthquakes

45. Transform – plates sliding horizontally past each other.
Found- California (San Andreas Fault)
Produces earthquakes!!
All plates

46. Hawaiian Islands
How they are formed
In action

47. Tsunami
How they are formed
Japan 2011