1. Plate Tectonics

2. Earth’s lithosphere is NOT one unbroken layer
It is like a cracked egg shell
Broken into pieces separated by jagged cracks

3. Tectonic or Crustal plates are segments of the Earth's crust
move relative to other segments
are characterized by volcanic and seismic activity around its margins.
The lithosphere is broken into separate sections called plates
move over the asthenosphere carrying pieces of continental and oceanic crust.

5. How Plates Move
The theory of plate tectonics states: pieces of Earth’s lithosphere are in slow, constant motion, driven by currents in the mantle
This explains the formation, movement and subduction of Earth’s plates

6. So, I got a question for ya…
How can Earth’s plates move?
What force is great enough to move the heavy continents?

7. By Geologists…I think you’ve got it!
The movement of currents in the mantle is the force that causes movement of the plates
As plates moves, they collide, pull apart, or grind past each other
This creates changes in Earth’s surface (volcanoes, mountain ranges, trenches)

8. Plate Boundaries Edge of Earth’s plates meet at plate boundaries
Extend deep into lithosphere
Faults – breaks in Earth’s crust where rocks have slipped past each other from along these boundaries

9. Plate Boundaries… 3 kinds of plate boundaries
Divergent boundaries
Convergent boundaries
Transform boundaries
A different type of movement occurs along each type of boundary
Plates move SLOW; from 1-24 cm per year (about as fast as your fingernails grow)

10. Divergent Boundaries Place where two plates move apart (diverge)
Most occur along mid-ocean ridge where sea-floor spreading occurs
Also occur on land
If this occurs, two of Earth’s plates slide apart creating a deep valley called a rift valley

11. Divergent Boundary along Ocean Ridge

12. Divergent Boundary along Land

13. Remember Density (Information only)
A. Density
1. The measure of how much mass is in a given volume
2. Density = Mass/Volume

14. Convergent Boundaries
Place where two plates come together (converge)
Result is a collision
The density of the plates determines which one comes out on top
If plate carrying oceanic crust (more dense) collides with plate carrying continental crust (less dense), the oceanic crust will sink (subduct) beneath continental crust

15. Convergent Boundaries
If two plates with continental crust collide, neither is dense enough to sink so the crust squeezes into mountain ranges
If two oceanic plates collide the older plate will sink since the older plate is more dense.

16. Convergent Boundaries (Oceanic vs. Continental)

17. Convergent Boundaries (Continental vs. Continental)

18. Convergent Boundaries (Oceanic vs. Oceanic)
older plate will sink (subduct)
Older crust is more dense

19. Transform Boundaries
Place where two plates slip past each other, moving in opposite directions
Where earthquakes often occur
Crust neither created nor destroyed

21. Review Questions Explain the theory of plate tectonics.
What type of plate boundary is it where two plates collide?
What do diverging plates form?
What is likely to occur at a plate boundary where oceanic crust collides with continental crust?
There are 2 islands on opposite sides of the mid-ocean ridge in the Atlantic Ocean. During the last 8 million years, the distance between the islands has increased by 200 kilometers. Calculate the rate at which the two plates are diverging. (in terms of centimeters per year)