1. Plate Tectonics

2. Brief Structure of the Earth
Divided into layers:
Core, mantle, crust

3. Brief Structure of the Earth
Lithosphere
Crust and upper part of the mantle
About 100 km thick
Rigid
Asthenosphere
Plastic (gooey) layer beneath the lithosphere
More dense than the lithosphere

4. Brief Structure of the Earth
Continental Crust
Made up of continents and “edges” of the oceans
Light
Oceanic Crust
Made up of ocean floor
More dense than continental crust
Older oceanic crust is more dense than younger oceanic crust

5. Theory of Plate Tectonics
Developed in 1960’s
Combined continental drift and seafloor spreading.

6. Theory of Plate Tectonics
Stated that:
The crust and upper mantle (lithosphere) of the earth are broken into sections called plates.
These plates sit on top of the plastic (gooey) part of the mantle (asthenosphere).
These plates can move apart, converge, or slide past one another through time.

8. Divergent Boundaries
Where plates are moving apart and new crust is forming.
Example: Mid-ocean ridges

9. Convergent Boundaries
Where two plates collide and crust is destroyed.
Subduction zone
Area where a dense oceanic plate sinks under a light continental plate or another less dense oceanic plate
Forms volcanoes.
When two continental plates collide high mountains are formed.

10. Transform Boundary Where one plate is sliding past another plate.
The plates may be going in opposite directions or the same direction at different rates.
Earthquakes are common

11. Modern Theories for Cause of Plate Tectonics
All include convection currents in the mantle.

12. Convection Current Cycle of heating, rising, cooling, sinking
Caused by differences in density due to differences in temperature
Example – boiling pan of water

13. Forces Movement of plates result in three types of forces:
Tension – pulls rocks apart
Compression – pushes rocks together
Shearing – pushes rocks past each other

14. Fault Surface where rock has broken apart and moved. 3 types
Normal fault
Reverse fault
Transform (or strike-slip) fault

15. Faults Normal fault Reverse fault Transform fault
Rock above the fault moves down.
Formed by tension.
Reverse fault
Rock above the fault plane moves up.
Formed by compression.
Transform fault
Bodies of rock slide past each other.
Formed by shearing.

16. Features of Tension Forces
Mid-ocean ridge
Where oceanic crust is being pulled apart.
Rift Valley
Where continental crust is being pulled apart.

17. Features of Compression Forces
Mountains
Continental-continental collisions
Very high mountains (folded mountains) are formed.
Oceanic-continental collisions
Volcanic mountains are formed.
Oceanic-oceanic collisions
Island arcs (volcanoes that reach above the surface of the ocean) are formed.

18. Features of Shearing Earthquakes
Rocks on each side of a strike-slip fault become stuck in one place for a time and then move, releasing energy in the form of an earthquake.

19. Tracking Plate Movement
Plate movement is tracked using satellites and lasers.
Current rates of movement range from about 1 cm to about 12 cm per year.