1. The Earth’s Crust in Motion…
Plate Tectonics
The Earth’s Crust in Motion…
Ch. 9

2. What’s the relationship here?
The Original Theory
In 1910, Alfred Wegener begins to wonder…
What’s the relationship here?
Perhaps these pieces (continents) used to be connected??
Ask the students to look closely at the map. “What does it remind you of?” When ‘puzzle’ is suggested introduce first line. Click on the image of Wegener for the hyperlink to USGS while discussing who he was. Continue to discuss Wegener’s theory and introduce continental drift definition.

3. (starting about 200 million years ago)
Wegener’s Theory
Continental drift = continents slowly moved over Earth’s surface
(starting about 200 million years ago)
Ask the students to look closely at the map. “What does it remind you of?” When ‘puzzle’ is suggested introduce first line. Click on the image of Wegener for the hyperlink to USGS while discussing who he was. Continue to discuss Wegener’s theory and introduce continental drift definition.

4. Supercontinent: all continents today connected into 1 large land
“Pangaea” – meaning all lands
Discuss the theory of Pangea and show animation (click on link).

5. Pangaea  Tens of Millions of years!
Discuss the theory of Pangea and show animation (click on link).

6. Evidence of Continental Drift
1. Continental Puzzle: coastlines of South America and Africa fit together

7. 2. Matching Fossils: Fossils of dinosaurs found on both sides of the Atlantic Ocean

8. 3. Rock Types:
Same mountain ranges found across oceans

9. 4. Ancient Climate:
Glaciers in South America, southern Africa, & Australia are found today in tropical climate areas (pg 252)

10. Rejecting Wegener’s Theory
Other Scientists rejected it …
It did NOT describe HOW the continents moved (just that they did) ? ? ? ? ? ?

11. NEW Theory
Over time … Technology advanced
Scientists mapped the ocean floor
More info on earthquakes
More info on Earth’s magnetic field

12. Plate Tectonics – EXPLAINS how it works!!!
Plates – pieces of the crust that move over the upper mantle
Plates fit closely together along cracks called Plate Boundaries
Convection Flow  movement of plates driven by unequal distribution of Earth’s heat
Explain that the lithosphere is broken into pieces called plates. The place where the pieces fit together are the boundaries. Using a laser pointer, explain the theory that plate movement is caused by convection currents in the mantle.

14. Earth’s Puzzle
Open the link to the USGS. Using a laser pointer, discuss the idea that the of plate boundaries. Ask the students to locate the plate that we live on. Ask the students to name the plates that our plate borders. They can write the answers on their handout of the slide show. Use the next hyperlink to answer the last question. With this page open, explain how the arrows depict the direction of movement of the plates.

15. How far do we move every year?
Open the link to the USGS. Using a laser pointer, discuss the idea that the of plate boundaries. Ask the students to locate the plate that we live on. Ask the students to name the plates that our plate borders. They can write the answers on their handout of the slide show. Use the next hyperlink to answer the last question. With this page open, explain how the arrows depict the direction of movement of the plates.

16. Types of Boundaries DIvergent CONvergent Transform
Define each term. Have the students as a class mimic the movement of divergent, convergent, and transform boundaries using their hands. Use the hyperlinks as visuals while discussing each type of plate boundary.
Transform

17. Divergent Boundaries: plates are moving apart
new crust is created
Magma is coming to the surface

18. Types of Divergent Boundaries
1. Rift valley- valley found along the edge

19. 2. Oceanic ridge (Sea floor spreading) - a ridge found on the ocean floor

20. Convergent Boundaries: plates are coming together
crust is returning to the mantle

21. Types of Convergent Boundaries
1. Ocean & Continent
Subduction - oceanic plate is pushed down under the crust/mantle (due to density differences)
Volcanic Arc volcanoes made by subduction

22. 2. Ocean & Ocean
volcanic island arc - a chain of small volcanic islands in ocean

23. 3. Continent & Continent
* Mountain range

24. Transform Boundaries: plates grind past each other
Crust is not created or destroyed
Ex) Stress builds up
Stress is released  Earthquake!!

25. Evidence for Plate Tectonics
1. Paleomagnetism: the natural magnetism in rocks (N - S or S - N)
Given by Earth’s magnetic field at the time the rock formed
normal polarity: a magnetic field that is the same as Earth’s present one
reverse polarity: a magnetic field opposite to Earth’s present field

27. Paleomagnetism of the Ocean Floor

28. More Evidence … 2. Earthquake Patterns
3. Ocean Drilling – age of sediment increases as move away from ridges

29. Hot Spots - area where magma rises up and causes volcanic activity
Ex) How volcanoes form away from plate boundaries -- Hawaiian Islands!