1. Plate Tectonics
The crust in motion

2. Evidence for Seafloor Spreading
Oceanic crust is younger than continental crust
Oceanic crust is 250 million years old while continental crust is almost 3 billion years old. Rocks are younger at the mid-ocean ridge and get increasingly older away from the ridge on both sides
Age of the Seafloor

3. Evidence for Seafloor Spreading (continued)
Magnetic Clues
Magnetic minerals in basaltic rocks align with the Earth’s magnetic field.
The magnetic field has reversed several times.

4. Theory of Plate Tectonics
Continental and Oceanic crust is broken up into sections called plates or tectonic plates that move over the Earth’s surface.

6. Layers Related to Plate Tectonics
Lithosphere
Asthenosphere
Consists of the crust and rigid upper mantle
Broken into large pieces called plates.
”Plastic”-like part of the upper mantle.
Convection occurs here.

7. Tectonic Plate Boundaries
3 Main Types of Boundaries
Divergent – plates move away from each other
Convergent – plates move toward each other
Transform – plates slide past each other horizontally

8. Divergent Boundaries Plates move away from each other
Examples of divergent boundaries are the Mid-Atlantic Ridge and the East-Pacific Rise
This is where Rifting occurs.

12. A plume of hot magma rises from deep within the mantle pushing up the crust and causing pressure forcing the continent to break and separate. Lava flows and earthquakes would be seen.

13. As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.

14. As the rift valley expands, water collects forming a sea.

15. The sea floor continues to spread and the plates get bigger and bigger.

17. Transform Plate Boundaries
Tectonic plates slide past each other with little or no vertical movement or subduction
Characteristics include:
- Major Earthquakes
An example of a transform boundary is the San Andreas fault in California

18. Transform Boundary Example

19. Diagram of Transform Boundary

20. Example of Transform Boundary