The Theory of Continental Drift

• Continental drift was proposed by Alfred Wegener• He used the following ideas to support his theory: • 1. The fit of the continents • 2. The distribution of fossils • 3. Similar sequence of rocks • 4. Ancient climates • 5. The wandering of the Earth's polar regions

• Wegener used his observations to hypothesize that all of the present-day continents were once part of a single supercontinent called Pangaea

The Fit of the Continents

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• Fossils of the same species were found on several different continents.

• For example, Glossopteris, a fern, was

found on the continents of South America, Africa, India, and Australia. If the continents are reassembled into Pangaea, the distribution of Glossopteris can be accounted for over a much smaller area.

Distribution of Similar Fossils

Continental Drift - Rock Sequences

Continental Drift - Glaciation

Sea-Floor Spreading

• In 1962, Harry Hess proposed that new ocean floor is formed at the mid-ocean ridges. The ocean floor is produced by magma that rises from the Earth’s interior.

• Hess suggested that the ocean floor moved away from the ridge and plunged into an oceanic trench along the continentals.