1. Plate Tectonics and Continental Drift

2. Continental Drift Alfred Wegener believed that the continents were once connected. This large continent was called Pangea. In 1915, he proposed his theory of Continental Drift.

3. Evidence For Continental Drift Matching fossils were found along the boundaries of continents that have very different climates. Glacial deposits found in South America, Africa, India, and Australia.

4. Sea Floor Spreading Theory With sonar, scientists determined that the ocean floor was composed of mountains and deep valleys. Harry Hess authored the Sea Floor Spreading Theory to explain that the ocean floor is constantly spreading along the Mid- Atlantic Ridge.

5. Mid-Atlantic Ridge New sea floor is created by oozing magma in the center of the MAR. Old sea floor is forced down into the mantle in the trenches near the boundaries of the oceans and continents. Rocks near the MAR were much younger than rocks that had been forced outward from the MAR.

6. Plate Tectonic Theory A new theory based on the Sea Floor Spreading Theory and The Continental Drift theory were combined to form the Plate Tectonic Theory. Plate Tectonic Theory: States that the earth’s crust and upper mantle are broken into sections called plates. The plates move around on the mantle.