1. Plate Tectonics

2. II. Restless Continents
A. Alfred Wegener
1. Alfred Wegener proposed the hypothesis of continental drift in the early 1900s.
2. Continental Drift: states that the continents once formed a single landmass, broke up, and drifted to their present locations.
Alfred Wegener (VAY guh nuhr)
Video clip

3. Continental Drift sim

4. B. Evidence for Continental Drift
1. Continental jigsaw puzzle.
Ex. South America/Africa
2. Rock Types and Structural Match
Ex. Matching mountain
ranges across the
North Atlantic.

5. 3. Fossil Match: Fossil of same species found in both South America and Africa.
a. Mesosaurus

6. b. Fossils of Glossopteris found in all of the southern continents.

7. 4. Ancient Climate: Glacier remnants.

8. He could not explain the mechanism that caused the continents to move.
►Wegener’s hypothesis was not supported by the scientific community.
He could not explain the mechanism that caused the continents to move.
The technology was not yet available to test his continental drift hypothesis.

9. C. Sea-Floor Spreading The Sea Floor is Spreading Video Clip
What technology did Harry Hess use to discover ocean mountain ranges?
What mechanism did Hess propose that drove continental movement?
Sea-floor spreading video

10. C. Sea-Floor Spreading 1. Harry Hess
During World War II, used sonar to map the ocean floor.
Found mid-ocean ridges.
Mid-ocean ridges are places where sea floor spreading occurs.

11. 2. Sea Floor Spreading
The process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies.
-A valid theory of how land masses could separate over time.
Web simulation

13. Magnetic Reversal and Sea-Floor Spreading
Seafloor Spreading and Magnetic Field Reversals

14. Magnetic reversal: Occurs when Earth’s magnetic poles change places.
(Present)