Passage 2 | Geslogy
Plate Tectonics Theory
From our fleeting human perspective, the configuration of Earth’s continents and oceans seems quite stable, and it is easy to assume that our world has always looked the same. For hundreds of years, scientists believed this to be true, but in the mid-twentieth century, evidence emerged proving that the Earth’s crust—oceans as well as continents—is slowly moving. While this is now accepted as fact, it was not always so. The first thinkers to suggest such concepts were ridiculed and their revolutionary ideas dismissed.
With the creation of accurate global maps, many people began to wonder about the remarkable relationship between the coastlines of eastern South America and western Africa. It appears that the two continents, if joined, would fit together perfectly. [A] This was essentially the birth of what would eventually become the theory of plate tectonics. 10 Of course, the shape of the continents was not the only peculiarity that encouraged speculation on this topic. [B] [C] Some scientists were intrigued by the close similarities in fossil remains found on separate continents—for example, in the northeastern United States and Scotland. [D] In the nineteenth and early twentieth centuries, the mainstream scientific community explained these findings by arguing that changing ocean levels sometimes exposed land bridges that connected the continents, allowing the overland migration of species.
Alfred Wegener, a German meteorologist with an interest in geology, found this theory lacking. He felt that land bridges could not adequately explain the close fossil matches discovered on opposite shores of the ocean. His curiosity on the subject led him to accumulate as much data as possible about rock and fossil samples uncovered throughout the world. In doing so, he encountered facts that further called the predominant theory into question. For example, fossils of various « tropical plants had been discovered in lands that now lie in the Arctic.
Wegener’s research led him in 1915 to introduce his theory of “continental drift,” the primary forerunner of plate tectonics. It stated that the continents had at one time been joined together in a huge supercontinent, and that this great landmass had broken apart and the separate continents had been drifting away from one another ever since. At the time, however, the idea received little support. Critics emphasized the failure of Wegener’s theory to sufficiently account for the means and causes of continental movement. His theory proposed that the landmasses moved independently of the rest of Earth’s crust, simply smashing through the solid rock of the seafloor, and no one, including Wegener, could come up with a force that would be great enough to drive this type of movement.
It was not until the 1950s and ’60s, when new technologies enabled scientists to study the ocean floor, that the main concept of Wegener’s theory was proven correct. In perhaps the most important discovery, researchers observed that, at some points on the seafloor, there were areas where it seemed like two sections of crust were moving apart from each other. In 1968 three American scientists used this discovery, along with other significant findings, to develop the theory of plate tectonics.
The theory holds that all of Earth’s crust is divided into several different plates, which are continuously moving at speeds of i between two and nine centimeters a year. Some are entirely underwater, while others comprise both oceans and continents. Their movement is caused by the Earth’s dynamic mantle, where molten material is constantly s rising and pushing on the plates. Geologists now believe that, over the millennia, these forces have caused Earth’s continents to come together numerous times to form supercontinents and then break apart again, o Because the plate tectonics theory provides such a comprehensive explanation of the mechanics of the Earth, it allows scientists to understand the causes of many natural phenomena. Earthquakes, volcanic eruptions, and the formation of mountains, for example, are all the results of plate movement.
Today, children learn about the plate tectonics theory in school, and most people take it for granted. However, it is beneficial to reflect on the long history of its progression. We should remember that revolutionary scientific ideas usually meet with heavy skepticism at first, but they sometimes prove to be major turning points in the ’25 understanding of our world.
14. The word configuration in the passage is closest in meaning to
15. The word dismissed in the passage is closest in meaning to
16. According to paragraph 2, maps played a role in the development of the plate tectonics theory by
(A) showing the paths of the moving continents
(B) helping scientists record the locations of different fossils
(C) stimulating curiosity about the parallels between coastlines
(D) outlining the locations of underwater land bridges
Paragraph 2 is marked with an arrow I«*].
17. Why does the author mention fossils of tropical plants found in the Arctic in paragraph 3?
(A) To provide an example of evidence that undermined an accepted theory
(B) To explain why the continental drift theory was not accepted at first
(C) To show how earlier scientists misunderstood the effects of Earth’s climate
(D) To demonstrate the problems encountered by Wegener during his research
18. According to the information in paragraph 3 and paragraph 4, how did Wegener’s theory explain the existence of similar fossils on different continents?
(A) By describing how the continents moved through the crust
(B) By suggesting that land bridges were present beneath the ocean
(C) By describing the migration patterns of the ancient species
(D) By suggesting that the continents were locked together at one time
Paragraph 3 and paragraph 4 are marked with arrows ^|.
19. The phrase account for in the passage is closest in meaning to
(A) conform to
(C) stand by
20. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
(A) Wegener’s theory stated that there was no known force capabie of causing the movement of the Earth’s crust.
(B) It was not logical to assume that landmasses could break through the thick crust found at the bottom of the ocean.
(C) Scientists were unable to identify any phenomenon that could cause the extraordinary continental movement described in Wegener’s theory.
(D) If Earth’s continents moved separately from the rest of the crust, there would have to be an incredibly powerful force at work.
21. According to paragraph 5, it can be inferred that the scientific study of Earth’s crust before 1950
(A) led to major discoveries about plate movement
(B) lacked information about the seafloor
(C) disproved the theory of continental drift
(D) made use of the latest technologies
Paragraph 5 is marked with an arrow [■*•!.
22. The word Their in the passage refers to
23. The word dynamic in the passage is closest in meaning to
24. According to paragraph 6, scientists determined that the forces responsible for plate movement originate
(A) within oceanic plates
(B) at earthquake sites
(C) in the Earth’s mantle
(D) near active volcanoes
Paragraph 6 is marked with an arrow [«*j.
25. Which of the following statements most accurately reflects the author’s opinion about science as expressed in paragraph 7?
(A) The evolution of a theory can be as educational as the theory itself.
(B) Most new ideas turn out to be major scientific innovations.
(C) Students should learn more about the history of science in school.
(D) Scientists should be less skeptical when considering new theories.
26. Look at the four squares ■ that indicate where the following sentence could be added to the passage.
It was hard to believe that the exact same animal and plant species would have existed simultaneously on such distant lands.
Where would the sentence best fit?
Click on a square [■ ] to add the sentence to the passage.
27. Directions: An introductory sentence for a brief summary of the passage is provided 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. This question is worth 2 points.
Though widely accepted today, it took many years for the basic concepts of the theory of plate tectonics to be established as fact.
(A) First inspired by the shapes of the continents as seen on maps, some scientists began to consider the idea of continental movement.
(C) Wegener’s theory of continental drift was an important step towards discovering plate tectonics, but it misunderstood the exact nature of the crust’s movement
(E) After observing the seafloor and discovering the importance of the mantle, scientists finally proved the existence of continental drift with the plate tectonics theory.
(B) Matching fossils found on separate
continents were used as evidence to suggest that the position of the continents was stable.
(D) Some technologies developed in the middle of the twentieth century gave researchers the means to gather information about the ocean floor.
(F) Before the establishment of the plate tectonics theory, phenomena such as earthquakes and volcanoes were not adequately explained by scientists.
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