1. Continental Drift: The Beginning of Plate Tectonics

2. Theory of Continental Drift

3. Continental Drift
Theory that the continents are drifting apart and towards each other
Alfred Wegener
Idea that all continents were all pieced together 245 million years ago
Pangaea = “All Earth”

4. Continental Drift

6. Argument for and against Continental Drift
Same fossils on different Continents
Rock formations
Climate conditions evidence
Glacial grooves on separated continents
Species could travel over “bridges”
Rock cycle occurs
Climate has cycles
Glaciers covered majority of Earth

7. Ultimate Question How could gigantic continents move?
What natural force could move entire continents?

8. An Answer: Sea Floor Spreading
Process in which new oceanic lithosphere is created as older material is pulled away
Process forces tectonic plates away from each other
Creates mid-ocean ridges which are underwater mountain chains

9. Sea-Floor Spreading

12. Evidence for Sea-Floor Spreading
Eruptions of molten material
Magnetic strips in the rock of the ocean floor
Ages of rock from drill samples

13. Magnetic Reversals Earth’s magnetic poles change place
Mineral grains of molten rock align to the poles of Earth
Rocks freeze trapping history of magnetic reversals

15. Question: ????
If new crust is being made at mid ocean ridges and the sea floor is spreading, then why isn’t the Earth’s surface getting larger?

16. Subduction at Plate Boundaries
Subduction is a process in which the dense ocean floor sinks back into the mantle
Occurs at deep-ocean trenches
Convergent boundaries

17. Quiz: What are the three layers of the Earth Based on Composition?
What are the 5 layers based on Structure?
What is Pangaea?
What process showed Continental Drift is correct?