Early Theories of Continental Drift

The idea that the past geography of Earth was different from today is not new. The earliest maps showing the east coast of South America and the west coast of Africa probably provided people with the first evidence that continents may have once been joined together, then broken apart and moved to their present positions.

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During the late nineteenth century, Austrian geologist Eduard Suess noted the similarities between the Late Paleozoic plant fossils of India, Australia, South Africa, and South America. The plant fossils comprise a unique group of plants that occurs in coal layers just above the glacial deposits on these southern continents. In this book The Face of the Earth (1885), he proposed the name “Gondwanaland” (called Gondwana here) for a supercontinent composed of the aforementioned southern landmasses. Suess thought these southern continents were connected by land bridges over which plants and animals migrated. Thus, in his view, the similarities of fossils on these continents were due to the appearance and disappearance of the connecting land bridges.

The American geologist Frank Taylor published a pamphlet in 1910 presenting his own theory of continental drift. He explained the formation of mountain ranges as a result of the lateral movements of continents. He also envisioned the present-day continents as parts of larger polar continents that eventually broke apart and migrated toward equator after Earth’s rotation was supposedly slowed by gigantic tidal forces. According to Taylor, these tidal forces were generated when Earth’s gravity captured the Moon about 100 million years ago. Although we know that Taylor’s explanation of continental drift is incorrect, one of his most significant contributions was his suggestion that the Mid-Atlantic Ridge—an underwater mountain chain discovered by the 1872-1876 British HMS Challenger expeditions—might mark the site at which an ancient continent broke apart, forming the present -day Atlantic Ocean.

However, it is Alfred Wegener, a German meteorologist, who is generally credited with developing the hypothesis of continental drift. In his monumental book, The Origin of Continents and Oceans (1915), Wegener proposed that all landmasses were originally united into a single supercontinent that he named “Pangaea.” Wegner portrayed his grand concept of continental movement in a series of maps showing the breakup of Pangaea and the movement of various continents to their present-day locations. What evidence did Wegener use to support his hypothesis of continental drift? First, Wegener noted that the shorelines of continents fit together, forming a large supercontinent and that marine, nonmarine, and glacial rock sequences of Pennsylvanian to Jurassic ages are almost identical for all Gondwana continents, strongly indicating that they were joined together at one time. Furthermore, mountain ranges and glacial deposits seem to match up in such a way that suggests continents could have once been a single landmass. And last, many of the same extinct plant and animal groups are found today on widely separated continents, indicating that the continents must have been in proximity at one time. Wegener argued that this vast amount of evidence from a variety of sources surely indicated the continents must have been close together at one time in the past.

Alexander Du Toit, a South African geologist was one of Wegener’s ardent supporters. He noted that fossils of the Permian freshwater reptile “Mesosaurus” occur in rocks of the same age in both Brazil and South Africa. Because the physiology of freshwater and marine animals is completely different, it is hard to imagine how a freshwater reptile could have swum across the Atlantic Ocean and then found a freshwater environment nearly identical to its former habitat. Furthermore, if Mesosaurus could have swum across the ocean, its fossil remains should occur in other localities besides Brazil and South Africa. It is more logical to assume that Mesosaurus lived in lakes in what are now adjacent areas of South America and Africa but were then united in a single continent.

Despite what seemed to be overwhelming evidence presented Wegener and later Du Toit and others, most geologists at the time refused to entertain the idea that the continents might have moved in the past.

【Paragraph 2】During the late nineteenth century, Austrian geologist Eduard Suess noted the similarities between the Late Paleozoic plant fossils of India, Australia, South Africa, and South America. The plant fossils comprise a unique group of plants that occurs in coal layers just above the glacial deposits on these southern continents. In this book The Face of the Earth (1885), he proposed the name “Gondwanaland” (called Gondwana here) for a supercontinent composed of the aforementioned southern landmasses. Suess thought these southern continents were connected by land bridges over which plants and animals migrated. Thus, in his view, the similarities of fossils on these continents were due to the appearance and disappearance of the connecting land bridges.

1. According to paragraph 2, Eduard Suess believed that similarities of plant and animal fossils on the southern continents were due to

A. living in the southern climate

B. crossing the land bridges

C. fossilization in the coal layers

D. movements of the supercontinent

【Paragraph 3】The American geologist Frank Taylor published a pamphlet in 1910 presenting his own theory of continental drift. He explained the formation of mountain ranges as a result of the lateral movements of continents. He also envisioned the present-day continents as parts of larger polar continents that eventually broke apart and migrated toward equator after Earth’s rotation was supposedly slowed by gigantic tidal forces. According to Taylor, these tidal forces were generated when Earth’s gravity captured the Moon about 100 million years ago. Although we know that Taylor’s explanation of continental drift is incorrect, one of his most significant contributions was his suggestion that the Mid-Atlantic Ridge—an underwater mountain chain discovered by the 1872-1876 British HMS Challenger expeditions—might mark the site at which an ancient continent broke apart, forming the present -day Atlantic Ocean.

2. According to paragraph 3, Frank Taylor believed that

A. present-day continents broke off from larger continents and drifted toward the poles due to tidal forces

B. the lateral shifting of continents caused the formation of mountain ranges

C. polar continents began to join together when Earth’s gravity captured the Moon 100 million years ago

D. Earth’s gravity and speed of rotation created large polar continents

3. Which of the following can be inferred from paragraph 3 about the Mid-Atlantic Ridge?

A. It was once above sea level.

B. It formed at the same time that Earth’s gravity captured the Moon.

C. It was much more extensive when it was first formed than it is today.

D. It was unknown before the HMS Challenger voyages.

【Paragraph 4】However, it is Alfred Wegener, a German meteorologist, who is generally credited with developing the hypothesis of continental drift. In his monumental book, The Origin of Continents and Oceans (1915), Wegener proposed that all landmasses were originally united into a single supercontinent that he named “Pangaea.” Wegner portrayed his grand concept of continental movement in a series of maps showing the breakup of Pangaea and the movement of various continents to their present-day locations. What evidence did Wegener use to support his hypothesis of continental drift? First, Wegener noted that the shorelines of continents fit together, forming a large supercontinent and that marine, nonmarine, and glacial rock sequences of Pennsylvanian to Jurassic ages are almost identical for all Gondwana continents, strongly indicating that they were joined together at one time. Furthermore, mountain ranges and glacial deposits seem to match up in such a way that suggests continents could have once been a single landmass. And last, many of the same extinct plant and animal groups are found today on widely separated continents, indicating that the continents must have been in proximity at one time. Wegener argued that this vast amount of evidence from a variety of sources surely indicated the continents must have been close together at one time in the past.

4. The word “monumental” in the passage is closest in meaning to

A. final

B. persuasive

C. well-known

D. great and significant

5. According to paragraph 4, Wegener felt confident that his theory are correct in part because

A. contemporary scientists were unable to successfully challenge his evidence

B. many different types of evidence seemed to support his theory

C. his theory accounted for phenomena that earlier theories could not explain

D. he had used the most advanced techniques available to gather his evidence

6. According to paragraph 4, Wegener pointed to all of the following in support of his theory of continental drift EXCEPT

A. Plants and animals now living on some continents appear to be descended from plants and animals that originated on other continents.

B. Rock sequences associated with the continents are extremely similar.

C. The coastlines of some continents seem to fit together.

D. Mountains on some continents would be adjacent to mountains on other continents if these continents were joined.

【Paragraph 5】Alexander Du Toit, a South African geologist was one of Wegener’s ardent supporters. He noted that fossils of the Permian freshwater reptile “Mesosaurus” occur in rocks of the same age in both Brazil and South Africa. Because the physiology of freshwater and marine animals is completely different, it is hard to imagine how a freshwater reptile could have swum across the Atlantic Ocean and then found a freshwater environment nearly identical to its former habitat. Furthermore, if Mesosaurus could have swum across the ocean, its fossil remains should occur in other localities besides Brazil and South Africa. It is more logical to assume that Mesosaurus lived in lakes in what are now adjacent areas of South America and Africa but were then united in a single continent.

7. Why does the author mention the fact that “the physiology of freshwater and marine animals is completely different”?

A. To explain why Du Toit was able to determine that Mesosaurus was a freshwater reptile

B. To explain why Du Toit concluded that certain fossils in rocks in Brazil and South Africa were those of the same animal

C. To cast doubt on the idea that Mesosaurus could have swum from one landmass to another

D. To show Du Toit determined which landmass Mesosaurus originated on

8. Which of the following can be inferred from paragraph 5 about the Permian Mesosaurus of Brazil and South Africa? 

A. It was the dominant animal in the habitats in which it lived.

B. It lived in similar environments in both places.

C. It was a weak swimmer compared with other freshwater reptiles.

D. Its physiology differed from that of modern freshwater reptiles.

【Paragraph 5】Alexander Du Toit, a South African geologist was one of Wegener’s ardent supporters. He noted that fossils of the Permian freshwater reptile “Mesosaurus” occur in rocks of the same age in both Brazil and South Africa. ■Because the physiology of freshwater and marine animals is completely different, it is hard to imagine how a freshwater reptile could have swum across the Atlantic Ocean and then found a freshwater environment nearly identical to its former habitat. ■Furthermore, if Mesosaurus could have swum across the ocean, its fossil remains should occur in other localities besides Brazil and South Africa. ■It is more logical to assume that Mesosaurus lived in lakes in what are now adjacent areas of South America and Africa but were then united in a single continent. ■

9. Look at the four squares【■】that indicates where the following sentence could be added to the passage.

In addition to supplying new geological evidence for continental drift, he crafted convincing arguments based on ancient life forms.

Where would the sentence best fit?

10. 【Directions】An introductory sentence for a brief summary of the passage is provides below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.

Several theories involving the movement of continents were proposed in the nineteenth and early twentieth centuries.

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Answer Choices

A. Early maps showing the coastlines of South America and Africa inspired Eduard Suess to search for fossil evidence that today’s southern continents had once been joined in a single landmass.

B. To Eduard Suess, continental drift accounted for the presence of the same types of fossils on different continents that had at times been connected by land bridges.

C. Du Toit’s study of the freshwater reptile Mesosaurus added to the already considerable body of evidence that Alfred Wegener had gathered in support of the idea of continental drift.

D. Frank Taylor expanded on Eduard Suess’s theory of continental drift by arguing that tidal forces 100 million years ago had broken continents apart and caused the rise of the Mid-Atlantic Ridge.

E. Alfred Wegener, who first developed the theory of continental drift argued that all landmasses were originally part of a supercontinent that broke up into separate continents.

F. Early theories of continental drift were not widely accepted at the time because they failed to explain why continents moved.