托福阅读常考话题及练习题推荐三：冰川（3）

► paragraph 5：Isotopic analysis of shells allowed geologists to measure another glacial effect. They could trace the growth and shrinkage of continental glaciers, even in parts of the ocean where there may have been no great change in temperature—around the equator, for example. The oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice. During glaciations, the lighter oxygen-16 has a greater tendency to evaporate from the ocean surface than the heavier oxygen-18 does. Thus, more of the heavy isotope is left behind in the ocean and absorbed by marine organisms. From this analysis of marine sediments, geologists have learned that there were many shorter, more regular cycles of glaciation and deglaciation than geologists had recognized from the glacial drift of the continents alone.

10. In can be inferred from paragraph 5 that foraminifera fossil shells containing calcite with high percentages of oxygen-16 were deposited at times when

A. polar ice extended as far as equatorial regions of land and sea

B. extensive glaciation was not occurring

C. there were no great increases in ocean temperature

D. there was heavy snowfall on continental glaciers

11. In paragraph 5, why does the author include the information that the “oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice” ?

A. To explain how scientists were able to calculate how frequently the continental ice sheets expanded and contracted

B. To explain how scientists have determined that there was no great change in ocean temperatures at the equator during past glaciations

C. To provide evidence that oxygen-16 has a greater tendency to evaporate than does oxygen-18

D. To suggest that equatorial marine organisms absorb more heavy isotopes than do marine organisms elsewhere

12. According to the passage, when did scientists begin to realize that more than one ice age had occurred?

A. In the mid nineteenth century

B. In the late nineteenth century

C. In the early twentieth century

D. In the late twentieth century

► Paragraph 1：In the middle of the nineteenth century, Louis Agassiz, one of the first scientists to study glaciers, immigrated to the United States from Switzerland and became a professor at Harvard University, where he continued his studies in geology and other sciences. For his research, Agassiz visited many places in the northern parts of Europe and North America, from the mountains of Scandinavia and New England to the rolling hills of the American Midwest. ■ In all these diverse regions, Agassiz saw signs of glacial erosion and sedimentation. ■ In flat plains country, he saw moraines (accumulations of earth and loose rock that form at the edges of glaciers) that reminded him of the terminal moraines found at the end of valley glaciers in the Alps. ■ The heterogeneous material of the drift (sand, clay, and rocks deposited there) convinced him of its glacial origin. ■

13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.

In his view, there could be no other explanation for the composition of such drift.

Where would the sentence best fit?

14. 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.

Louis Agassiz was the first to note signs of glacial erosion and sedimentation in diverse regions of Europe and North America.

Answer Choices

A. Evidence of a pattern of glacier-like deposits eventually convinced most geologists that an enormous continental glacier had extended into the temperate zone.

B. Glacial research showed that many layers of ice were deposited, with each new period of glaciation extending farther south than the one before.

C. Isotopic analysis of marine sediments showed that periods of glaciation and deglaciation were more frequent, shorter, and more cyclic than previously thought.

D. Nineteenth-century geologists came to accept the idea that the areas covered by polar ice had reached as far as the equator, a far larger area than Agassiz had thought.

E. Nineteenth-century geologists studying the layers of drift concluded that during the Pleistocene epoch, several glaciations had occurred with warm periods between them.

F. Research involving foraminifera fossil shells show that ocean temperatures in the Northern Hemisphere varied greatly during the most extensive periods of glaciation.

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