Theory of Continental Drift

• Theory of Plate Tectonics

Theory of Continental Drift

• The Theory of Plate Tectonics starts with another idea… Continental Drift. The Earth once had a single land mass called Pangaea that broke apart into pieces that drifted away to become the major continents of today.

• Pangaea

Evidence that supports Continental Drift

• Identical types of fossils found in Africa and South America
• Continents can “piece”together with the same rock formations
• Glacial deposits left by same sheet of ice

• Africa-South America

The continents are moving because of sea floor spreading.

• Running down the middle of the oceans are long mountain chains with valleys in the middle called mid ocean ridges. Lava erupts from the center of the valley and pushes the ocean floor away on the other side. The Mid-Atlantic Ridge is separating at approximately 4 cms per year.

More evidence…

• Rocks are younger by the mid ocean ridge than farther away
• Magnetic stripes match up on either side of the ridge as the poles reverse themselves

• Magnetic Stripes