托福 Z托福 46 - Extinction of the dinosaurs
题目
1 2 3 4 5 6 7 8 9 10 11 12 13 14
14.main idea
A.Cosmic rays from a nearby supernova explosion may have penetrated Earth’s atmosphere, causing genetic changes that dinosaur populations could not survive.
B.Climate changes in the tropics may have set off a chain of indirect effects that negatively affected the ecosystems in which dinosaurs lived.
C.The spread of lava over large parts of previously favored habitats such as the Deccan Plateau may have made these favored areas uninhabitable for many years.
D.Although the volcanic winter resulting from the formation of sulfate aerosols eventually ended, temperatures may have remained below levels required by dinosaurs to survive.
E.Temperature changes and geographic shifts in climate zones due to the atmospheric effects of volcanic activity may have been significant enough to cause extinction.
F.To be convincing, theories about what caused dinosaurs to become extinct must be able to explain the disappearance of other predators in the food chain at the same time.
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Geologists define the boundary between sediment layers of the Cretaceous period (144..C65 million years ago) and the Paleocene period (65..C55 million years ago) in part by the types and amounts of rocks and fossils they contain or lack. Before the limit of 65 million years ago, marine strata are rich in calcium carbonate due to accumulations of fossils of microscopic algae deposited on the sea floor. Above the 65-million-year limit, sea-floor sediments contain much less calcium carbonate, and fossils of several families of mollusks are no longer found. In continental sediments, dinosaur fossils, though frequent before 65 million years ago, are totally absent. By contrast, new families of mammals appear, including large mammals for the first time.

Scientists wondered for many years about what could have caused the dinosaurs’ rapid disappearance at the end of the Cretaceous period, coming up with a great variety of theories and scenarios. For some, it could have been due to unfavorable genetic changes triggered by a dramatic increaseby a factor of 10, 100, 1,000 in cosmic-ray particles reaching the Earth after a supernova explosion somewhere in the neighborhood of the solar system. For these high-energy particles to affect life, they would have to get through the protective barrier of the Earth’s magnetosphere, the region of the upper atmosphere controlled by Earth’s magnetic field. That could have happened if the cloud of particles from the supernova explosion reached the Earth during a period when the magnetosphere was weakened, something that may happen when the Earth’s magnetic field changes direction. And we know that the magnetic north and south poles of the Earth switch on the average twice every million years. However, this is not the only possible explanation for dinosaur destruction.

Other theories have raised the possibility of strong climate changes in the tropics (but they then must be explained). Certainly, if climate changes, the changed distributions of temperature and rainfall modify the conditions that favor one ecosystem over another. The extinction of a particular family, genus, or species may result from a complicated chain of indirect causes and effects. Over thirty years ago, scientist Carl Sagan quoted one suggestion that the demise of the dinosaurs resulted from the disappearance of a species of fern plant that was important for dinosaur digestion. Other theories involved a worldwide cold wave following the spread of a layer of cold but not very salty water in the world’s oceans, which floated on the surface because, with its low salinity, the water was less dense.

Proponents of another theory that remains under consideration today postulate that the extinction of the dinosaurs corresponds to a period of intense volcanic activity. It’s not a question of just one or even of a thousand eruptions comparable to the explosion of Krakatoa in 1883, one of the largest volcanic events in modern times, but rather of a prolonged period of activity. On the Deccan plateau in India, basalt (volcanic) rocks cover more than 500, 000 square kilometers (nearly 200, 000 square miles), and correspond to massive lava outflows occurring precisely at the end of the Cretaceous. This sort of outflow could correspond to volcanic activity similar to the activity that drives sea-floor spreading, with lava emerging from elongated fractures in the crust rather than from craters.

The volcanic convulsion that buried the Deccan plateau in lava must also have changed the composition of the atmosphere and severely affected climate. Initially, there must have been strong sudden cooling resulting from the blocking of sunlight by sulfate aerosol veils in the stratosphere (part of the Earth’s atmosphere). If strong cooling lasted a year after the formation of the aerosols, it would have been the death of tropical species unable to adapt to such a volcanic winter.

However, a long period of strong volcanic activity (again, remember thousands of Krakatoas) would at the same time have added a substantial amount of carbon dioxide to the atmosphere, reinforcing the greenhouse effect. This would gradually warm things up, ending the extended cold snap and producing global warming together with geographic shifts of humid and arid (dry) zones. Certainly things would change to upset living conditions, leading to the extinction of some species while others would profit, if only from the disappearance of predators.

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最新提问
  • wx_6697
    觉得B C 意思一样,不知道选哪个
  • wx_5576
    这道题C为什么对,E为什么不对?
  • wx_5576
    B为什么不能选啊?
  • wx_6697
    TPO30 passage 2 Q5我选的 D,不明白为啥不对?
  • wx_6697
    鑫哥,TPO6passage3Q5 答案是给错了吗?好多人都选A
  • wx_6697
    这题也很容易选错选成了D
  • wx_6697
    这道题A为什么错了
  • 芊儿
    为什么这道题不选c??a中的variety不是应该对应文中的differentiating 吗??求解!
  • wx_1000
    这道题不选E是因为太细节了吗
  • 王金阁
    这个题为什么不选C啊。。。
  • 芊儿
    这道题的D选项不是和文中的better able to reproduce in open settings相对应么??
  • 风荨火
    有大佬解释一下这个为啥选D嘛?
  • 以沫
    请问这个D 在哪里提现?为什么D错?
  • 芊儿
    第六题 的C选择为什么不对,感觉A是明显驳斥啊...
  • wx_6697
    鑫哥,这道题D是从哪里看出来的
  • wx_6697
    这题选的A,根据是Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.想问鑫哥为啥不选A
  • wx_6697
    这题我选的是C依据是into a new habitat outside of its natural range, it may adapt to the new environment and leave its enemies behind.C为啥错了呢?鑫哥
  • wx_8861
    F选项的weather-related destruction在哪里体现了呢?原文最后一段的开头Among the costs里的costs是不是打错了?应该是coast?
  • wx_6697
    求问这道题B为啥不选,原文依据:viable seeds of pioneer species can be found in large numbers on some forest floors.
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    与托福的斗争史 去解答 去解答
    这题为什么选C?
  • 小雨淅沥哗啦的下
    小雨淅沥哗啦的下 去解答 去解答
    B哪里错了
  • 小雨淅沥哗啦的下
    小雨淅沥哗啦的下 去解答 去解答
    B为啥不对
  • 李浩然
    B选项错误,是因为残缺么?
  • wx_100
    请问在做题的时候如何排除c呢。看了答案,感觉是该选a的,但是当时做题脑子一热,就特别钟爱c,也没看其他选项。。求敲醒。。
  • wx xxxxx
    请问鑫哥,这段开头有写As one pesticide replaces another为什么不是对应a new pesticide is developed?
  • wx_7695
    鑫哥,从哪里看出来这个masks 不是use呀,原文说了wear呀
  • haiyuqiao
    @鑫哥,这题the damage will continue 不应该对应前面的 the target species evolves resistance to it,然后As one pesticide replaces another,不应该是结束了time cycle 吗
  • wx_2065
    鑫哥,想知道E错在哪里?
  • wx_7695
    鑫哥,B选项 cannot extended to earlier geological periods. 原文说的意思是后来的进化无法估计吧
  • wx_2163
    B为什么不选
  • wx_7780
    鑫哥,这个哪里看不use了。BD是修饰错,C是无中生有,怎么能直接选出A?
  • 100
    看到第一句话,以为是中心句就选了A... 为什么不能选A呢
  • 100
    为什么选b?
  • gu33
    请问下 这里选D的原因是 因为 evolutionary approach 对应着 原文的 Rates of evolution 嘛? 这里我选了C。。不是很懂 插入句和 D的关系 求解答
  • 我是啦啦啦
    我是啦啦啦 去解答 去解答
    这个题A哪里错了?是因为主语不对吗?这个C比A多一步推理啊
  • haiyuqiao
    鑫哥,D选项里的19世纪出现了很多假设,原文中并没有提到啊
  • wx_7060
    为什么选a 呢。我觉得a是细节。F哪错了?
  • wx_1105
    我想问一下,这道题为什么不能选A呢?
  • wx_8122
    D为什么不选
  • wx_1655
    f选项哪里说了
  • chaulaw
    鑫哥,原文是below经济损害水平,D是一触发经济损害就用,这也对吗?
  • chaulaw
    interclan婚姻是对的吗?不是只在自己的family结婚扩大家族吗?
  • wx_6697
    鑫哥,这道题答案是不是错了,好多人选D 我也选的D求解答
  • wx_6697
    这道题应该是一道易错题,每个选项的都有,然而我选的A错了,求解
  • wx_6697
    鑫哥,这题的C是怎么得到的?B也没有找到啊?难道不是应该选B
  • wx_6697
    鑫哥,还有这个,好多人选A答案是不是错了
  • wx_6697
    求问D是从哪里得出来的,我选的B呀哎呀
  • wx_4185
    it is difficult to say how far they were intended to be portraits rather than generalized images 这句话怎么理解呢
  • 此楠楠
    请问下这个插入题怎么选的呢?
  • 此楠楠
    求鑫哥讲解下A选项。。。 Even though in error, Joly’s calculations clearly supported those geologists who insisted on an age for Earth far in excess of a few million years.