1. EQ: What is the theory of plate tectonics?

2. EQ: What is the theory of plate tectonics?
Plates
A section of the lithosphere that slowly moves, carrying pieces of continental and oceanic crust
The plates fit closely together along cracks in the crust
Plates carry the continents or parts of the ocean floor, or both

3. EQ: What is the theory of plate tectonics?
Scientific Theory
A well – tested concept that explains a wide range of observations
EQ: What is the theory of plate tectonics?

4. EQ: What is the theory of plate tectonics?
A geological theory that states that pieces of Earth’s crust are in constant, slow motion, driven by convection currents in the mantle
Convection Currents: The movement of a fluid, caused by differences in temperature and density, that transfers heat from one part of the fluid to another
EQ: What is the theory of plate tectonics?

5. How can Earth’s plates move?
The plates of the lithosphere float on the top of the asthenosphere
Convection currents rise in the asthenosphere and spread out beneath the lithosphere
Geologists believe this causes plate movement
EQ: What is the theory of plate tectonics?

6. EQ: What is the theory of plate tectonics?
As plates move, they collide, pull apart, or grind past each other, producing spectacular changes in the earth’s surface.
EQ: What is the theory of plate tectonics?

7. EQ: What is the theory of plate tectonics?
These changes include volcanoes, mountain ranges, deep sea trenches, and earthquakes.
EQ: What is the theory of plate tectonics?

8. EQ: What is the theory of plate tectonics?
Figure 26: Interpreting Maps Which plates include only ocean floor? Which plates include both continents and ocean floor?
Plates that include only ocean floor are the Pacific Plate and the Nazca Plate
All other labeled plates in the figure include both continents and ocean floor
EQ: What is the theory of plate tectonics?

9. EQ: What is the theory of plate tectonics?
Study the map of Earth’s plates in Figure 26. Notice the arrows that show the direction of plate movement. Now find the Nazca plate on the map. What direction is it moving?
The Nazca plate is moving east
EQ: What is the theory of plate tectonics?

10. Find the South American plate and describe its movement.
The South American plate is moving west
EQ: What is the theory of plate tectonics?

11. What do you think will happen as these plates continue to move?
If the plates continue to move, they will collide (convergent boundary)
Since the Nazca plate carries oceanic crust and the South American plate carries continental crust, the Nazca will plunge beneath the South American plate
EQ: What is the theory of plate tectonics?

12. EQ: What is the theory of plate tectonics?
Faults
A break in the Earth’s crust where slabs of rock slip past each other
EQ: What is the theory of plate tectonics?

13. three types of plate boundaries
EQ: What is the theory of plate tectonics?
three types of plate boundaries
Transform Boundaries
Divergent Boundaries
Convergent Boundaries
At each type of plate boundary, there is a different type of plate movement

14. EQ: What is the theory of plate tectonics?
Transform Boundaries
A plate boundary where two plates move past each other in opposite directions
Crust is neither created nor destroyed
EQ: What is the theory of plate tectonics?

15. What Earth changing event occurs on a transforming boundary?
Earthquakes frequently occur at transform boundaries
EQ: What is the theory of plate tectonics?

16. EQ: What is the theory of plate tectonics?
Divergent boundaries
A plate boundary where two plates move away from each other
Most divergent boundaries occur at the mid-ocean ridge
Divergent boundaries that occur on land are called rift valleys
Example: Great Rift Valley (South Africa)
A 3,000 km crack in the earth
EQ: What is the theory of plate tectonics?

17. EQ: What is the theory of plate tectonics?
Rift Valleys
A rift valley is a deep valley that forms along a divergent boundary on land
Rift valleys form as two slabs of Earth’s crust slide apart

18. What could eventually happen at the Great Rift Valley in Africa?
The rift may someday split the eastern part of Africa away from the rest of the continent
EQ: What is the theory of plate tectonics?

19. Convergent Boundaries
A plate boundary where two plates move toward each other
Collisions can occur between:
oceanic crust and oceanic crust
oceanic crust and continental crust
continental crust and continental crust
EQ: What is the theory of plate tectonics?

20. EQ: What is the theory of plate tectonics?
When two plates collide, the density of the plates determines which one comes out on top.

21. What occurs when plates carrying oceanic crust collide?
The more dense plate dives back into the mantle (subduction)
The collision between oceanic plates causes deep-ocean trenches
EQ: What is the theory of plate tectonics?

22. EQ: What is the theory of plate tectonics?
What occurs when plates carrying oceanic and continental crust collide?
The more dense oceanic crust sinks and plunges (subducts) beneath the less dense continental crust
The collision between oceanic plates and continental plates can cause a volcanic eruption
EQ: What is the theory of plate tectonics?

23. What occurs when plates carrying continental crust collide?
Plates crash head – on causing mighty mountain ranges
EQ: What is the theory of plate tectonics?

25. What types of plate movement occur at plate boundaries?
Plates slip past each other at transform boundaries
Move apart at divergent boundaries
Come together at convergent boundaries
EQ: What is the theory of plate tectonics?

26. Plates move at a rate of between one and ten centimeters per year.
EQ: What is the theory of plate tectonics?

27. EQ: What is the theory of plate tectonics?
The North American and Eurasian plates float away from each other at a rate of fingernail growth. This is a rate of 2.5 centimeters per year.

28. EQ: What is the theory of plate tectonics?
Figure 29: Posing Questions What questions would you need to answer in order to predict where the continents will be in 50 million years?
You would need answers to how fast and in what direction each plate is moving
EQ: What is the theory of plate tectonics?