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Plate Tectonics and Continental Drift 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. 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. 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 MidAtlantic Ridge. 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. 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.