1. PLATE TECTONICS

2. Objectives
Explain how paleomagnetism provided the definitive evidence for continental drift.
Define seafloor spreading.
Define theory of plate tectonics.
Describe the different types of plate margins.
Explain the role of mantle convection in plate tectonics.

3. A Revolution in Geology
Continental drift
Proposed by Alfred Wegener
Slow, lateral movement of continents along Earth’s surface
The puzzle piece argument
Pangaea
Continental shelf
Continental slope

4. Matching Geology Matching rocks
What is the “true” edge of a continent?

5. Matching Geology
Matching rocks
How well do the continents fit?

6. Matching Geology
Matching rocks
How well do the ages match?

7. Matching Geology

8. Matching Geology
Matching rocks
What evidence did the glaciers leave?

9. Matching Geology Matching fossils
What evidence did the glaciers leave?
Glossopteris: ancient tree with large seeds found on several continents
Mesosaurus: small reptile found in Brazil and S. Africa

10. Matching Geology

11. Apparent Polar Wandering Paths
Paleomagnetism
Apparent polar wandering
Magnetic poles wandered
Used to indicate America and Europe were a single continent

12. Apparent Polar Wandering Paths

13. Seafloor Spreading The missing clue Seafloor spreading
The process by which the seafloor splits and moves apart along a midocean ridge
New oceanic crust forms along the ridge
Global Positioning Systems (GPS) valuable tool

15. The Plate Tectonic Model
The movement and interactions of large fragments of Earth’s lithosphere (i.e. plates)
Below lithosphere- asthenosphere
Weak due to hot temperature (near melting point)
Relationship between lithosphere and asthenosphere is isostasy
Fault
A fracture in Earth’s crust along which movement has occurred

16. The Plate Tectonic Model

17. Types of plate margins Divergent margins
A boundary along which two plates move apart from one another

18. Types of plate margins Convergent margin
A boundary along which two plates come together

19. Types of plate margins Subduction zone
A boundary along which one lithosphere plate plunges into the mantle beneath another plate
“Collision zone” between continents
Deep oceanic trenches
Arcs of volcanoes

20. Types of plate margins Transform vault
A fracture in the lithosphere where two plates slide past each other

21. Earthquake and plate margins
Tectonic movement produce pressure and friction.
Friction is overcome, the block slips and pent up energy releases with a huge “snap”
Focus
Where earthquake begins
Epicenter
Point on earth’s center directly over the focus

23. The search for a mechanism
Earth’s internal heat
Conduction
Slow release of heat
Convection
A form of heat transfer in which hot material circulates from hotter to colder regions, looses its heat, and then repeats the cycle

25. The tectonic cycle Tectonic cycle
Movements/ interactions by which rocks are cycled from the mantle to the crust and back
Includes earthquakes, volcanism, and plate motion, driven by convection in the mantle
As a result, seafloor recycles itself every 200 million years

26. The tectonic cycle

27. Hawaiian Islands

28. Critical Thinking
What are some of the important questions about plate tectonics that remain unanswered today?
Why do geologists call plate tectonics a “unifying theory”?
As Africa slowly separated from Arabia, and the sea began to enter the rift, what kind of sediment would you expect to be deposited?