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第一次在CD上发帖子，不会排版各位凑合着看看呗
【原文】
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 suffi ciently 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 suffi cient 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 confi gurations of the bodies in the solar system. Yet the lack of information about other possible factors affecting
global climate does not make them unimportant.
【题目】
It can be inferred from the passage that the isotope
record taken from ocean sediments would be less
useful to researchers if which of the following were
true?
(A) It indicated that lighter isotopes of oxygen
predominated at certain times.
(B) It had far more gaps in its sequence than the
record taken from rocks on land.
(C) It indicated that climate shifts did not occur
every 100,000 years.
(D) It indicated that the ratios of oxygen 16 and
oxygen 18 in ocean water were not consistent
with those found in fresh water.
(E) It stretched back for only a million years.
【OA】B
当时错选了E，因为以为第三段100,000years就是million。。做的时候把这道题作为逻辑题来看，排除B的原因是定位到第三段的：Second, it is a more continuous record than that taken from rocks on land. 我觉得这就是题目给出的premise，而B选项直接否定了这个premise，我当时想这么简单粗暴不会吧，按照CR的方法不是不能这么干的嘛？？还是说CR的理论不完全适用于RC呢？？求各位好心的NN解答~
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发表于 2019-4-24 10:39:51
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