1. Three ways tectonic plates interact:
Converge (collide)
Diverge (move apart)
Slide past one another (“Transform Boundary”)

2. What’s Inside the Earth?

3. 2 types: Ocean and Continental Crust
OCEAN crust
Denser
Thinner
Eventually subducted
Relatively young
CONTINENTAL crust
Less dense
Thicker
Rarely/never subducted
Oldest crust on Earth

4. 1912- Theory of Continental Drift
Continents were formed from the drifting apart of one super continent: Pangaea
Alfred Wegener

5. Theory of Continental Drift
The shape of continents seemed to “fit” together

6. Found evidence of similar fossils and geological formations on different continents

7. Geologic Evidence
Big flaw with this theory: How did the continents actually move?

8. Seafloor Spreading
In 1962, Hess proposed seafloor spreading as the mechanism for continents to actually drift.
Hess proposed that new ocean crust was being created along the Mid Ocean Ridges. As ocean crust collided with other plates, it was subducted and thus destroyed and recycled.

9. Theory of Plate Tectonics
Outer “shell” of Earth is broken into plates
Plates are carried by convection cells in mantle
Moving plates collide, diverge, or slide by each other

10. https://youtu.be/kwfNGatxUJI

11. Convection cells in (upper mantle) cause sea floor spreading

13. Convergent Boundaries
1. Continental/Oceanic
Denser ocean crust is subducted (pulled) under
Deep trenches, mountains, strong earthquakes
Melting oceanic plates turn into magma
Examples:
Andes Mts.
Cascade Mts.

14. Convergent Boundaries
2. Oceanic/Oceanic
Slower plate is subducted (pulled under)
Outcome = volcanic islands, strong earthquakes, tsunamis, deep trenches
Ex: Aleutian islands (Alaska), Japan, Southeast Asia

15. Convergent Boundaries
3. Continental/Continental
Continental Crust is light, so no subduction
Instead, piles of crumpled, folded crust = tall mountains
Examples: Himalayan Mts.,
Appalachian Mts.,
Alps

16. Himalayan Formation

17. Divergent Boundary Normal Fault Mostly below the ocean
Sea Floor Spreading - Forms new crust
Example: Mid
Atlantic Ridge, Rift
Valley in Africa

18. Great Rift Valley- Africa

19. Age of Seafloor: Red is newest, green oldest

20. Transform Plate Boundaries
2 plates sliding in opposite directions
E.g. San Andreas Fault

21. Major Tectonic Plates