Continental Drift

Chapter 9.1

The Continental Puzzle

• For 300 years, people noticed that the continents looked like pieces of puzzle

• In 1915, Alfred Wegener proposed that all the continents had been joined together to form one continent called, Pangaea.

• This hypothesis was called “Continental Drift”.

Evidence for Continental Drift

• Matching Fossils• Rock Types• Ancient Climates

Evidence #1: Matching Fossils

• Several fossil organisms found on different landmasses that could not have crossed the ocean

• Ex: Mesosaurus, a fresh water reptile has fossil remains in South America and Africa

• Ex: Glossopteris, a plant fossil found in South America, Africa, and India

• Ex: Lystrosaurus, a land reptile. S.A. & Africa

How did they get there?

• Some thought that maybe the animals had crossed on land bridges that are now underwater.

• However, there are no signs of any land bridges in the Atlantic Ocean

• Wegener concluded that the landmasses had been joined in the past.

Evidence #2: Rock Types

• If the continents were once part of Pangaea, the rocks found in a particular region on one continent should closely match in age and type the adjoining region

• Matching types of rocks in several mountain belts that are separated today be oceans are evidence of continental drift.

Rock Type Example

• The Appalachians in North America and the Mountains in the British Isles and Scandinavia

• Rocks in those mountains are the same age and type

• Form a continuous belt if you put North America next to Europe.

Evidence #3: Ancient Climates- Glaciers

• Between 220 mya and 300 mya ice sheets covered large areas of the Southern Hemisphere- South Africa, South America, India, Australia.

• If the continents had not moved, then the ice would have had to move from the sea to land (very unusual)

• The ice movement makes more sense if Pangaea had been connected with Antarctica

Ancient Climates- Tropical Swamps

• Between 220 mya & 300 mya there were tropical swamps in North America, Europe, and Siberia.

• Because it was warm in these areas at this time, Wegener decided that there was not an ice age causing the glaciers.