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Milankovitch proposed in the early twentieth century that the ice ages were caused by variations in the Earth’s orbit around the Sun. For some time this theory was considered untestable, largely because there was no sufficiently precise chronology of the ice ages with which the orbital variations could be matched. To establish such a chronology it is necessary to determine the relative amounts of land ice that existed at various times in the Earth’s past. A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down. As an indicator of shifts in the Earth’s climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land. Because of these advantages, sedimentary evidence can be dated with sufficient accuracy by radiometric methods to establish a precise chronology of the ice ages. The dated isotope record shows that the fluctuations in global ice volume over the past several hundred thousand years have a pattern: an ice age occurs roughly once every 100,000 years. These data have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages. However, it is important to note that other factors, such as volcanic particulates or variations in the amount of sunlight received by the Earth, could potentially have affected the climate. The advantage of the Milankovitch theory is that it is testable; changes in the Earth’s orbit can be calculated and dated by applying Newton’s laws of gravity to progressively earlier configurations of the bodies in the solar system. Yet the lack of information about other possible factors affecting global climate does not make them unimportant.
我还是把原文章贴出来。 71. The author of the passage would be most likely to agree with which of the following statements about the Milankovitch theory? (A) It is the only possible explanation for the ice ages. (B) It is too limited to provide a plausible explanation for the ice ages, despite recent research findings. (C) It cannot be tested and confirmed until further research on volcanic activity is done. (D) It is one plausible explanation, though not the only one, for the ice ages. (E) It is not a plausible explanation for the ice ages, although it has opened up promising possibilities for future research.
Application Th e author’s reaction to the statements about the Milankovitch theory must be based on how the author treats the theory in the passage. Th e fi rst, second, and third paragraphs describe the theory and the use of a new research method to test the theory. Th e passage states that data from these tests have established a strong connection between variations in the Earth’s orbit and the periodicity of the ice ages, suggesting that the author of the passage believes the theory is plausible. In the fi nal paragraph, the author points to other factors that might be involved, suggesting that the theory might not provide a complete explanation.
我的问题是,plausible 是看是正确的,就是实际上是错误的。 这里很明显作者的意思的 M这个人的point是正确的,只是不完全。我觉得plausible 是个负评价的词语。虽然在答案中D答案的结构是非他莫属。但是还是让我理解起来很困难。我觉得D 应该是not plausible explaination。。。。。
请nn解答。谢谢~! |
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