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One of the central scientific questions of nineteenth-century geology was the origin of mountains. How were they formed? What process squeezed and folded rocks like bread dough? What made Earth’s surface move? Most theories invoked terrestrial contraction as a causal force. It was widely believed that Earth had formed as a hot, incandescent body and had been steadily cooling since the beginning of geological time. Because most materials contract as they cool, it seemed logical to assume that Earth had been contracting as it cooled, too. As it did, its surface would have deformed, producing mountains. In Europe, Austrian geologist Eduard Suess (1831–1914) popularized the image of Earth as a drying apple: as the planet contracted, its surface wrinkled to accommodate the diminished surface area. Suess assumed that Earth’s initial crust was continuous but broke apart as the interior shrank. The collapsed portions formed the ocean basins, the remaining elevated portions formed the continents. With continued cooling, the original continents became unstable and collapsed to form the next generation of ocean floor, and what had formerly been ocean now became dry land. Over the course of geological history, there would be a continual interchange of land and sea, a periodic rearrangement of the landmasses. The interchangeability of continents and oceans explained a number of other perplexing geological observations, such as the presence of marine fossils on land (which had long before puzzled Leonardo da Vinci) and the extensive interleaving of marine and terrestrial sediments in the stratigraphic record. Suess’s theory also explained the striking similarities of fossils in parts of Africa and South America. Indeed, in some cases the fossils seemed to be identical, even though they were found thousands of miles apart. These similarities had been recognized since the mid-nineteenth century, but they had been made newly problematic by Darwin’s theory of evolution. If plants and animals had evolved independently in different places within diverse environments, then why did they look so similar? Suess explained this conundrum by attributing these similar species to an early geological age when the continents were contiguous in an ancient supercontinent called Gondwanaland. Suess’s theory was widely discussed and to varying degrees accepted in Europe, but in North America geologist James Dwight Dana (1813–1895) had developed a different version of contraction theory. Dana suggested that the continents had formed early in Earth history, when low-temperature minerals such as quartz and feldspar had solidified. Then the globe continued to cool and contract, until the high-temperature minerals such as olivine and pyroxene finally solidified–on the Moon, to form the lunar craters; on Earth, to form the ocean basins. As contraction continued after Earth was solid, its surface began to deform. The boundaries between continents and oceans were most affected by the pressure, and so mountains began to form along continental margins. With continued contraction came continued deformation, but with the continents and oceans always in the same relative positions. Although Dana’s theory was a version of contraction, it came to be known as permanence theory, because it viewed continents and oceans as globally permanent features. In North America permanence theory was linked to the theory of subsidence (or sinking) of sedimentary basins along continental margins. This idea was developed primarily by paleontologist James Hall (1811–1898), who noted that beneath the forest cover, the Appalachian Mountains of North America were built up of folded layers of shallowwater sedimentary rocks, thousands of feet thick. How did these sequences of shallow-water deposits form? How were they folded and uplifted into mountains? Hall suggested that materials eroded off the continents accumulated in the adjacent marginal basins, causing the basins to subside. Subsidence allowed more sediment to accumulate, causing more subsidence, until finally the weight of the pile caused the sediments to be heated, converted to rock, and then uplifted into mountains. Dana modified Hall’s view by arguing that thick sedimentary piles were not the cause of subsidence but the result of it.Either way, the theory provided a concise explanation of how thick sequences of shallow-water rocks could accumulate, but was vague on the question of how they were transformed into mountain belts. 1. According to paragraph 1, most nineteenth-century theories of mountain formation were based on which of the following ideas? A. The heat released at the time of Earth’s formation caused rocks to fold. B. Earth’s surface expanded and stretched because the planet had become hot. C. Earth’s surface shrank and deformed as the planet cooled over time. D. Movements of Earth’s surface due to frequent expansion and contraction pushed rocks upward. ►In Europe, Austrian geologist Eduard Suess (1831–1914) popularized the image of Earth as a drying apple: as the planet contracted, its surface wrinkled to accommodate the diminished surface area. Suess assumed that Earth’s initial crust was continuous but broke apart as the interior shrank. The collapsed portions formed the ocean basins, the remaining elevated portions formed the continents. With continued cooling, the original continents became unstable and collapsed to form the next generation of ocean floor, and what had formerly been ocean now became dry land. Over the course of geological history, there would be a continual interchange of land and sea, a periodic rearrangement of the landmasses. 2. For which of the following purposes did Suess use the image of “a drying apple”? A. To show that Earth’s crust had to have been continuous at first B. To show how the processes that led to the formation of ocean basins differed from those that led to the formation of continents C. To prove that Earth’s continents and ocean floors were not stable D. To explain how Earth’s surface wrinkled over a shrunken interior ►The interchangeability of continents and oceans explained a number of other perplexing geological observations, such as the presence of marine fossils on land (which had long before puzzled Leonardo da Vinci) and the extensive interleaving of marine and terrestrial sediments in the stratigraphic record. Suess’s theory also explained the striking similarities of fossils in parts of Africa and South America. Indeed, in some cases the fossils seemed to be identical, even though they were found thousands of miles apart. These similarities had been recognized since the mid-nineteenth century, but they had been made newly problematic by Darwin’s theory of evolution. If plants and animals had evolved independently in different places within diverse environments, then why did they look so similar? Suess explained this conundrum by attributing these similar species to an early geological age when the continents were contiguous in an ancient supercontinent called Gondwanaland. 3. According to paragraph 3, how did Suess explain the occurrence of similar fossils on various continents? A. Continents and oceans exchanged materials, so the fossil record was not unique to a specific region. B. Initially the landmasses that make up today’s continents were one continuous landmass. C. The species associated with these fossils gradually spread across the world’s continents. D. Coastal terrestrial sediments contained similar fossils across continents. ►The interchangeability of continents and oceans explained a number of other perplexing geological observations, such as the presence of marine fossils on land (which had long before puzzled Leonardo da Vinci) and the extensive interleaving of marine and terrestrial sediments in the stratigraphic record. Suess’s theory also explained the striking similarities of fossils in parts of Africa and South America. Indeed, in some cases the fossils seemed to be identical, even though they were found thousands of miles apart. These similarities had been recognized since the mid-nineteenth century, but they had been made newly problematic by Darwin’s theory of evolution. If plants and animals had evolved independently in different places within diverse environments, then why did they look so similar? Suess explained this conundrum by attributing these similar species to an early geological age when the continents were contiguous in an ancient supercontinent called Gondwanaland. 4. Why does the author mention “Darwin’s theory of evolution” in the passage? A. To explain why fossils in the stratigraphic record seemed to be identical B. To indicate that other scientists did not accept Suess’s theory of interchangeability C. To point out a complication that Suess had to resolve for his theory to be valid D. To prove that similar species had existed on different continents at an early geological age ►In Europe, Austrian geologist Eduard Suess (1831–1914) popularized the image of Earth as a drying apple: as the planet contracted, its surface wrinkled to accommodate the diminished surface area. Suess assumed that Earth’s initial crust was continuous but broke apart as the interior shrank. The collapsed portions formed the ocean basins, the remaining elevated portions formed the continents. With continued cooling, the original continents became unstable and collapsed to form the next generation of ocean floor, and what had formerly been ocean now became dry land. Over the course of geological history, there would be a continual interchange of land and sea, a periodic rearrangement of the landmasses. 5.Select the TWO answer choices that mention how Dana’s theory about Earth’s contraction described in paragraph 4 was different from Suess’s theory described in paragraph 2. To receive credit, you must select TWO answers A. According to Dana, continents formed before ocean basins. B. According to Dana, continents and ocean basins maintained the same relative positions. C. According to Dana, Earth stopped contracting after its surface cooled and became solid. D. According to Dana, mountains were formed by the cooling of high-temperature minerals. ►In North America permanence theory was linked to the theory of subsidence (or sinking) of sedimentary basins along continental margins. This idea was developed primarily by paleontologist James Hall (1811–1898), who noted that beneath the forest cover, the Appalachian Mountains of North America were built up of folded layers of shallowwater sedimentary rocks, thousands of feet thick. How did these sequences of shallow-water deposits form? How were they folded and uplifted into mountains? Hall suggested that materials eroded off the continents accumulated in the adjacent marginal basins, causing the basins to subside. Subsidence allowed more sediment to accumulate, causing more subsidence, until finally the weight of the pile caused the sediments to be heated, converted to rock, and then uplifted into mountains. Dana modified Hall’s view by arguing that thick sedimentary piles were not the cause of subsidence but the result of it.Either way, the theory provided a concise explanation of how thick sequences of shallow-water rocks could accumulate, but was vague on the question of how they were transformed into mountain belts. 6. The word “adjacent” in the passage is closest in meaning to A. open B. extra C. deep D. nearby ►The interchangeability of continents and oceans explained a number of other perplexing geological observations, such as the presence of marine fossils on land (which had long before puzzled Leonardo da Vinci) and the extensive interleaving of marine and terrestrial sediments in the stratigraphic record. 7. 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. The presence of marine fossils on land as well-as the distribution of marine and terrestrial sediments had long been a mystery to Leonardo da Vinci. B. The interchangeability of the continents and oceans as well as other geological observations had long been a source of confusion. C. The continual rearrangement of land and sea provided an explanation for some other mysterious geological observations. D. The interchangeability of continents and oceans explained the, absence of fossils orcor sediments in oceans. ►In North America permanence theory was linked to the theory of subsidence (or sinking) of sedimentary basins along continental margins. This idea was developed primarily by paleontologist James Hall (1811–1898), who noted that beneath the forest cover, the Appalachian Mountains of North America were built up of folded layers of shallowwater sedimentary rocks, thousands of feet thick. How did these sequences of shallow-water deposits form? How were they folded and uplifted into mountains? Hall suggested that materials eroded off the continents accumulated in the adjacent marginal basins, causing the basins to subside. Subsidence allowed more sediment to accumulate, causing more subsidence, until finally the weight of the pile caused the sediments to be heated, converted to rock, and then uplifted into mountains. Dana modified Hall’s view by arguing that thick sedimentary piles were not the cause of subsidence but the result of it.Either way, the theory provided a concise explanation of how thick sequences of shallow-water rocks could accumulate, but was vague on the question of how they were transformed into mountain belts. 8. According to paragraph 5, which of the following led James Hall to propose a theory of subsidence? A. The gradual sinking of the Appalachian Mountains resulting from the forests covering them B. The existence of sedimentary basins along continental margins C. The apparent subsidence of mountains due to erosion D. The notion that the Appalachian Mountains are formed of thick, folded layers of sedimentary rock In North America permanence theory was linked to the theory of subsidence (or sinking) of sedimentary basins along continental margins. This idea was developed primarily by paleontologist James Hall (1811–1898), who noted that beneath the forest cover, the Appalachian Mountains of North America were built up of folded layers of shallowwater sedimentary rocks, thousands of feet thick. How did these sequences of shallow-water deposits form? How were they folded and uplifted into mountains? Hall suggested that materials eroded off the continents accumulated in the adjacent marginal basins, causing the basins to subside. ⬛ Subsidence allowed more sediment to accumulate, causing more subsidence, until finally the weight of the pile caused the sediments to be heated, converted to rock, and then uplifted into mountains. ⬛ Dana modified Hall’s view by arguing that thick sedimentary piles were not the cause of subsidence but the result of it. ⬛ Either way, the theory provided a concise explanation of how thick sequences of shallow-water rocks could accumulate, but was vague on the question of how they were transformed into mountain belts. ⬛ 9. Look at the four squares■ that indicate where the following sentence could be added to the passage. More acceptable explanations of how mountains actually formed emerged after the development of the theory of plate tectonics. Where would the sentence best fit? Click on a square to add the sentence to the passage. 10. During the nineteenth century, several prominent geologists attempted to explain the origin of mountains on Earth. Answer Choices A. Many scientists believed that mountains were formed early in geological time while Earth was still a hot body. B. Continents may have developed early with the formation of rocks and remained constant while mountains formed at their edges as Earth shrank. C. One theory postulated that sedimentary rock forming at the edge of continents first sank under its own weight, then rose to form mountains. D. It was suggested that as Earth’s hot crust cooled, it cracked and formed interchanging continents and oceans. E. Some a mountainous areas are made up of layers of sedimentary rocks, which may explain how mountains rose as Earth cooled. F. The presence of marine fossils on land and of similar fossils in different parts of the world resulted from the early formation of a supercontinent. |
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