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OFFICIAL33 Which of the following can be inferred from paragraph 4 about the meteorite theory?

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Extinction Episodes of The Past
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It was not until the Cambrian period, beginning about 600 million years ago, that a great proliferation of macroscopic species occurred on Earth and produced a fossil record that allows us to track the rise and fall of biodiversity. Since the Cambrian period, biodiversity has generally risen, but there have been some notable exceptions. Biodiversity collapsed dramatically during at least five periods because of mass extinctions around the globe. The five major mass extinctions receive most of the attention, but they are only one end of a spectrum of extinction events. Collectively, more species went extinct during smaller events that were less dramatic but more frequent. The best known of the five major extinction events, the one that saw the demise of the dinosaurs, is the Cretaceous-Tertiary extinction.

Starting about 280 million years ago, reptiles were the dominant large animals in terrestrial environments. In popular language this was the era “when dinosaurs ruled Earth,” when a wide variety of reptile species occupying many ecological niches. However, no group or species can maintain its dominance indefinitely, and when, after over 200 million years, the age of dinosaurs came to a dramatic end about 65 million years ago, mammals began to flourish, evolving from relatively few types of small terrestrial animals into the myriad of diverse species, including bats and whales, that we know today. Paleontologists label this point in Earth’s history as the end of the Cretaceous period and the beginning of the Tertiary period, often abbreviated as the K-T boundary. This time was also marked by changes in many other types of organisms. Overall, about 38 percent of the families of marine animals were lost, with percentages much higher in some groups Ammonoid mollusks went from being very diverse and abundant to being extinct. An extremely abundant set of planktonic marine animals called foraminifera largely disappeared, although they rebounded later. Among plants, the K-T boundary saw a sharp but brief rise in the abundance of primitive vascular plants such as ferns, club mosses, horsetails, and conifers and other gymnosperms. The number of flowering plants (angiosperms) was reduced at this time, but they then began to increase dramatically.

What caused these changes? For many years scientists assumed that a cooling of the climate was responsible, with dinosaurs being particularly vulnerable because, like modern reptiles, they were ectothermic (dependent on environmental heat, or cold-blooded). It is now widely believed that at least some species of dinosaurs had a metabolic rate high enough for them to be endotherms (animals that maintain a relatively consistent body temperature by generating heat internally). Nevertheless, climatic explanations for the K-T extinction are not really challenged by the ideas that dinosaurs may have been endothermic, because even endotherms can be affected by a significant change in the climate.

Explanations for the K-T extinction were revolutionized in 1980 when a group of physical scientists led by Luis Alvarez proposed that 65 million years ago Earth was stuck by a 10-kilometer-wide meteorite traveling at 90,000 kilometers per hour. They believed that this impact generated a thick cloud of dust that enveloped Earth, shutting out much of the incoming solar radiation and reducing plant photosynthesis to very low levels. Short-term effects might have included huge tidal waves and extensive fires. In other words, a series of events arising from a single cataclysmic event caused the massive extinctions. Initially, the meteorite theory was based on a single line of evidence. At locations around the globe, geologists had found an unusually high concentration of iridium in the layer of sedimentary rocks that was formed about 65 million years ago. Iridium is an element that is usually uncommon near Earth’s surface, but it is abundant in some meteorites. Therefore, Alvarez and his colleagues concluded that it was likely that the iridium in sedimentary rocks deposited at the K-T boundary had originated in a giant meteorite or asteroid. Most scientist came to accept the meteorite theory after evidence came to light that a circular formation, 180 kilometers in diameter and centered on the north coast of the Yucatan Peninsula, was created by a meteorite impact about 65 million years ago. 

12.Which of the following can be inferred from paragraph 4 about the meteorite theory?

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正确答案:B
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【题目翻译】以下哪一项可以从关于陨石理论的第4段中推断出来? A:最初作为理论证据的数据最终被拒绝了。 B:很多科学家在第一次提出时不接受它。 C:它还没有被广泛接受作为对K-T灭绝的解释。 D:阿尔瓦雷斯随后在尤卡坦半岛发现了一个圆形构造后对其进行了修改。 【判定题型】:根据题干中出现的关键词“imply”/“infer”/“suggest”等其他表示推断的词,判定本题为推理题。 【关键词定位】没有特别好的关键词,需要整段理解Passage4。 【逻辑分析】从这句话:Initially, the meteorite theory was based on a single line of evidence. 得知,一开始仅依赖于单一证据的理论, 暗示了证据还不够充分。而后文章说找到了高浓度的iridium (铱), 理论有了证据的支持,从“Most scientists came to accept the meteorite theory after evidence came to light that a circular formation, 180 kilometers in diameter and centered on the north coast of the Yucatan Peninsula, was created by a meteorite impact about 65 million years ago. ”这句话可以知道,在环形坑证据出现之后大多数的科学家才开始接受小行星撞击理论, 也就是说一开始大多数科学家对该理论是持有怀疑态度的。 【选项分析】 A.没有被拒绝,虽然一开始科学家们是持有怀疑态度的,但是最终逐渐接受了,故选项错误。 B.文中的“科学家的怀疑态度”与选项B相对应,故B选项正确。 C.文中“科学家们逐渐接受了陨星理论,因为他们看到了六千五百万年前陨星撞击产生的圆形构造的证据。”选项不符合文章原意,故错误。 D.文章未提及“revised”,故错误。

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