Chapter 7: Plate Tectonics

Table of ContentsTable of Contents

Section 1. Continental Drift

Evidence for Continental Drift• If you look at a map of Earth’s surface, you

can see that the edges of some continents look as though they could fit together like a puzzle.

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A. Pangaea

1. German meteorologist Alfred Wegener (VEG nur) proposed the hypothesis of continental drift in 1912.

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2. According to the Wegener’s hypothesis of continental drift, continents have moved slowly to their current locations.

A. Pangaea3. Wegener suggested that all continents once

were connected as one landmass that broke apart about 200 million years ago.

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4. He called this large landmass Pangaea (pan JEE uh), which means “all land.”

B. A Controversial Idea

1. Wegener’s hypothesis on continental drift was controversial idea. He did not have enough evidence.

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B. A Controversial Idea

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2. Wegener proposed that the continents plowed through the ocean floor, driven by the spin of Earth.

3. Physicists and geologists of the time pointed out that continental drift would not be necessary to explain many of Wegener’s observations.

4. It wasn’t until long after Wegener’s death in 1930 that his basic hypothesis was accepted.

C. Fossil Clues

1. Fossils are the remains, imprints, or traces of prehistoric organisms. They can tell when and where organisms once lived and how they lived.

2. Animal fossils offer one clue that the continents might have been joined together millions of years ago.

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C. Fossil Clues

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3. For example, fossils of the reptile Mesosaurus have been found in South America and Africa.

C. Fossil Clues

4. This swimming reptile lived in freshwater and on land.

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5. How could fossils of Mesosaurus be found on land areas separated by a large ocean of salt water?

6. Wegener hypothesized that this reptile lived on both continents when they were joined.

D. A Widespread Plant

1. Another fossil that supports the hypothesis of continental drift is Glossopteris (glahs AHP tur us).

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2. This fossil plant has been found in Africa, Australia, India, South America, and Antarctica.

D. A Widespread Plant

3. The presence of Glossopteris in so many area also supported Wegener’s idea that all of these regions once were connected and had similar climates.

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E. Climate Clues

1. Scientists have found fossils of warm-weather plants on the island of Spitsbergen in the Arctic Ocean. This is one of the coldest place on Earth.

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2.To explain this, Wegener’s hypothesis of continental drift proposed that Spitsbergen Island drifted from tropical regions to the arctic.

F. Rock Clues

1. Glaciers are large, slow moving bodies of ice on land.

2. Glacial deposits and rock surfaces scoured and polished by glaciers are found in South America, Africa, India, and Australia.

3. This shows that parts of these continents were covered with glaciers in the past.

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F. Rock Clues4. Similar rock structures are

found on different continents.

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5. For example, parts of the Appalachian Mountains of the eastern United States are similar to those found in Greenland and western Europe.

6. Rock clues like these support the idea that the continents were connected in the past.

G. How could continents drift?

1. Although Wegener provided evidence to support his hypothesis of continental drift, he couldn’t explain how, when, or why these changes took place.

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G. How could continents drift?

2. Because other scientists could not provide explanations either, Wegener’s idea of continental drift was initially rejected.

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3. After Wegener’s death, new technology provided new evidence. New ideas about continental drift were developed. One of these ideas is called seafloor spreading. You’ll learn more about this in the next section.

Section CheckSection Check

Question 1

__________ is the hypothesis that continents have slowly moved to their current locations.

A. Continental driftB. Mid-ocean shiftingC. PangaeaD. Seafloor spreading

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Question 2

Who proposed the hypothesis of continental drift?

A. EskerB. GagarinC. HessD. Wegener

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Question 3

What is Pangaea?

End of Chapter Summary File