TPO 19-3 Discovering the Ice Ages（自然科学--冰河世纪）

字数：685

建议做题时间20分钟

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.

The areas covered by this material were so vast that the ice that deposited it must have been a continental glacier larger than Greenland or Antarctica. Eventually, Agassiz and others convinced geologists and the general public that a great continental glaciation had extended the polar ice caps far into regions that now enjoy temperate climates. For the first time, people began to talk about ice ages. It was also apparent that the glaciation occurred in the relatively recent past because the drift was soft, like freshly deposited sediment. We now know the age of the glaciation accurately from radiometric dating of the carbon-14 in logs buried in the drift. The drift of the last glaciation was deposited during one of the most recent epochs of geologic time, the Pleistocene, which lasted from 1.8 million to 10,000 years ago. Along the east coast of the United States, the southernmost advance of this ice is recorded by the enormous sand and drift deposits of the terminal moraines that form Long Island and Cape Cod.

It soon became clear that there were multiple glacial ages during the Pleistocene, with warmer interglacial intervals between them. As geologists mapped glacial deposits in the late nineteenth century, they became aware that there were several layers of drift, the lower ones corresponding to earlier ice ages. Between the older layers of glacial material were well-developed soils containing fossils of warm-climate plants. These soils were evidence that the glaciers retreated as the climate warmed. By the early part of the twentieth century, scientists believed that four distinct glaciations had affected North America and Europe during the Pleistocene epoch. 

This idea was modified in the late twentieth century, when geologists and oceanographers examining oceanic sediment found fossil evidence of warming and cooling of the oceans. Ocean sediments presented a much more complete geologic record of the Pleistocene than continental glacial deposits did. The fossils buried in Pleistocene and earlier ocean sediments were of foraminifera—small, single-celled marine organisms that secrete shells of calcium carbonate, or calcite. These shells differ in their proportion of ordinary oxygen (oxygen-16) and the heavy oxygen isotope (oxygen-18). The ratio of oxygen-16 to oxygen-18 found in the calcite of a foraminifer's shell depends on the temperature of the water in which the organism lived. Different ratios in the shells preserved in various layers of sediment reveal the temperature changes in the oceans during the Pleistocene epoch.

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.

题目

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答案解析

1. 词汇题

解析：accumulation积累、沉淀，选D

2. 词汇题

解析：heterogeneous多相的、混杂的，选B。原句说heterogeneous物质，括号中列举了多种物质，说明应该是多种物质，选B

3. 事实信息题

解析：根据persuade定位到最后一句，说这些漂流物中各种物质让他相信它们来自冰川，而前文说他去到很多地方，都发现了冰川的迹象，所以是在不同区域相似的冰川物质让他认为冰川的覆盖面广，选B

4. 词汇题

解析：enjoy温和的气温，应该是有、经历的意思，选A

5. 推断题

解析：本段第5句说我们现在通过漂流物的碳14知道了冰河时期的准确时间，可推断出在A这个时期这是不知道的，选B

6. 事实信息题

解析：根据well-developed soils定位到第3句，说的是发现本身，后句说这些土壤证明后退的冰川是因为气候变暖，而段首句说多个冰河世纪之间有比较暖的时期，所以这里由土壤可以得到的结论的冰河世纪之间有较温和的时期，选B

7. 事实信息题

解析：第4段段首句说这个想法改变了，当海洋变暖变冷的化石被发现时，所以选A

8. 词汇题

解析：reveal揭示，选C

9. 事实信息题

解析：根据forminifera定位到第3句及之后，说通过氧16和氧18的比例可以知道P这个时期的温度变化（最后一句），选D

10. 推断题

解析：根据氧16定位到During glaciations这句，说在冰川形成时期，氧16更容易蒸发，氧18更容易沉积留在海洋中并被生物吸收，也就是冰川时期氧18的比例更高。题干说氧16比例很高，可以推断这个时期并没有大量形成冰川，选B。

11. 修辞目的题

解析：这句话说的是氧的同位素比例会随着水的蒸发而变化，前句说分析同位素可以追踪冰川的增加和降低，所以高亮部分解释了科学家如何能够知道冰川的过大和收缩，选A

12. 事实信息题

解析：第3段第2句说在19世纪玩具地质学家绘制冰川沉积物时意识到漂流物有多层，低层对应更早的冰河时期，说明这个时候就已经知道冰河时期不止一次，选B

13. 句子插入题

解析：插入句提到in his view，说明前文提到过一个男人；提到no other explanation，说明前文有一种解释；提到such drift，说明前文提到过drift的内容。ABC前都是对Agassiz的事实描述，D前说漂流物中多种物质让他相信它们是由冰川而来，这句话是对漂流物来源的解释，选D

14. 段落小结题

解析：A对应第2段，正确

B原文没有这个比较，不选

C对应第5段，正确

D原文没说，不选

E对应第3段，正确

F原文没说，不选

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