托福备考托福阅读34套TPO样题+解析+译文15--2 Mass Extinctions物种灭绝
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托福阅读TPO15(试题+答案+译文)第2篇:Mass Extinctions物种灭绝
托福阅读原文
【1】Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. There was one such event at the end of the Cretaceous period(around 70 million years ago). There was another, even larger, mass extinction at the end of the Permian period (around 250 million years ago). The Permian event has attracted much less attention than other mass extinctions because mostly unfamiliar species perished at that time.
【2】The fossil record shows at least five mass extinctions in which many families of marine organisms died out. The rates of extinction happening today are as great as the rates during these mass extinctions. Many scientists have therefore concluded that a sixth great mass extinction is currently in progress.
【3】What could cause such high rates of extinction? There are several hypotheses, including warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents. Biological hypotheses include ecological changes brought about by the evolution of cooperation between insects and flowering plants or of bottom-feeding predators in the oceans. Some of the proposed
mechanisms required a very brief period during which all extinctions suddenly took place; other mechanisms would be more likely to have taken place more gradually, over an extended period, or at different times on different continents. Some hypotheses fail to account for simultaneous extinctions on land and in the seas. Each mass extinction may have had a different cause.Evidence points to hunting by humans and habitat destruction as the likely causes for the current mass extinction.
【4】American paleontologists David Raup and John Sepkoski, who have studied extinction rates in a number of fossil groups, suggest that episodes of increased extinction have recurred periodically, approximately every 26 million years since the mid-Cretaceous period. The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes. The possibility that mass extinctions may recur periodically has given rise to such hypotheses as that of a companion star with along-period orbit deflecting other bodies from their normal orbits, making some of them fall to Earth as meteors and causing widespread devastation upon impact.
【5】Of the various hypotheses attempting to account for the late Cretaceous extinctions, the one that has attracted the most attention in recent years is the asteroid-impact hypothesis first suggested by Luis and
Walter Alvarez. According to this hypothesis, Earth collided with an asteroid with an estimated diameter of 10kilometers, or with several asteroids, the combined mass of which was comparable. The force of collision spewed large amounts of debris into the atmosphere, darkening the skies for several years before the finer particles settled. The reduced level of photosynthesis led to a massive decline in plant life of all kinds, and this caused massive starvation first of herbivores and subsequently of carnivores. The mass extinction would have occurred very suddenly under this hypothesis.
【6】One interesting test of the Alvarez hypothesis is based on the presence of the rare-earth element iridium (Ir).Earth’s crust contains very little of this element, but most asteroids contain a lot more. Debris thrown into the atmosphere by an asteroid collision would presumably contain large amounts of iridium, and atmospheric currents would carry this material all over the globe. A search of sedimentary deposits that span the boundary between the Cretaceous and Tertiary periods shows that there is a dramatic increase in the abundance of iridium briefly and precisely at this boundary. This iridiumanomaly offers strong support for the Alvarez hypothesis even though no asteroid itself has ever been recovered.
【7】An asteroid of this size would be expected to leave an immense crater, even if the asteroid itself was disintegrated by the impact. The intense
heat of the impact would produce heat-shocked quartz in many types of rock. Also, large blocks thrown aside by the impact would form secondary craters surrounding the main crater.To date, several such secondary craters have been found along Mexico’s Yucatan Peninsula, and heat-shocked quartz has been found both in Mexico and in Haiti.A location called Chicxulub, along the Yucatan coast, has been suggested as the primary impact site.
托福阅读试题
1.Paragraph 1 supports which of the following statements about mass extinctions?
A.They take place over a period of 70 million years.
B.They began during the Cretaceous period.
C.They eliminate many animal species that exist at the time they occur.
D.They occur every 250 million years.
2.According to paragraph 2, scientists base their belief that a mass extinction is going on at present on which of the following?
A.The speed with which mass extinctions are happening today is similar to the speed of past extinctions.
B.The number of species that have died out since the last extinction event is extremely large.
C.Mass extinctions occur with regularity and it is time for another one.
D.Fossil records of many marine species have disappeared.
3.The word extended in the passage is closest in meaning to
A.specific.
B. unlimited.
C.reasonable.
D. long.
4.According to paragraph 3, each of the following has been proposed as
a possible cause of mass extinctions EXCEPT
A.habitat destruction.
B.continental movement.
C.fierce interspecies competition.
D.changes in Earth's temperature.
5.Paragraph 3 supports which of the following ideas about mass extinctions?
A.Scientists know the exact causes of most mass extinctions.
B.Mass extinctions are unlikely to happen again in the future.
C.Insects, flowering plants, and bottom-feeding predators in the oceans tend to be the first organisms to disappear during episodes of mass extinctions.
D.Some mass extinctions occurred on land and in the seas at the same time.
6.Which of the sentences below best expresses the essential information in the underlined sentence （Paragraph 4）in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.Based on their studies of extinction rates of numerous fossil groups, paleontologists David Raup and John Sepkoski have determined that mass extinctions occur about every 26 million years.
B.David Raup and John Sepkoski studied extinction rates of numerous fossil groups and suggest that mass extinctions during the Cretaceous period continued for 26 million years.
C.Studies that paleontologists David Raup and John Sepkoski conducted of various fossil groups have revealed that extinction rates have increased over the past 26 million years.
D.The studies conducted by paleontologists David Raup and John Sepkoski of the fossil remains of species suggest that the extinction rate of species started to increase by the middle of the Cretaceous period. 7.According to paragraph 4, what aspect of extinction episodes does the companion-star hypothesis supposedly clarify?
A.Their location.
B.Their frequency.
C.Their duration.
D.Their severity.
8.The phrase account for in the passage(Paragraph 5)is closest in meaning to
A.describe.
B.challenge.
C.explain.
D.test.
9.According to paragraph 6, what made iridium a useful test of the Alvarez hypothesis?
A.Its occurrence in a few locations on Earth against several locations on other planets.
B.Its occurrence in limited quantities on Earth against its abundance in asteroids.
C.Its ability to remain solid at extremely high temperatures.
D.Its ease of detection even in very small amounts.
10.In stating that no asteroid itself has ever been recovered, the author emphasizes which of the following?
A.The importance of the indirect evidence for a large asteroid.
B.The fact that no evidence supports the asteroid impact hypothesis.
C.The reason many researchers reject the Alvarez hypothesis.
D.The responsibility of scientists for not making the effort to discover the asteroid itself.
11.The word intense（Paragraph 7）in the passage is closest in meaning
to
A.sudden.
B.unusual.
C.immediate.
D. extreme.
12.What is the purpose of paragraph 7 in the passage?
A.It proposes a decisive new test of the Alvarez hypothesis.
B.It presents additional supporting evidence for the Alvarez hypothesis.
C.It explains why evidence relating to the Alvarez hypothesis is hard to find.
D.It shows how recent evidence has raised doubts about the Alvarez hypothesis.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. Where would the sentence best fit? In general, it is believed that these two extinctions resulted from drastic environmental changes that followed meteorite impacts or massive volcanic eruptions.
■Cases in which many species become extinct within a geologically short interval of time are called mass extinctions. ■There was one such event at the end of the Cretaceous period (around 70 million years ago). ■There was another, even larger, mass extinction at the end of the Permian period (around 250 million years ago). ■The Permian event has attracted much
less attention than other mass extinctions because mostly unfamiliar species perished at that time.
14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
There have been many attempts to explain the causes of mass extinctions.
A.Asteroid impacts, evolutionary developments, and changes in Earth's climate and in the positions of the continents have all been proposed as possible causes of mass extinctions.
B.Researchers have observed 26-million-year cycles in extinction rates of a number of fossil groups that could all be attributed to the same cause.
C.According to the Alvarez hypothesis, much of the iridium originally present on Earth was thrown into the atmosphere as a result of an asteroid impact that also caused a mass extinction.
D.The unusual distribution of iridium on Earth and the presence of craters and heat-shocked quartz are central to the theory that an asteroid impact caused the late Cretaceous event.
E.The collision between Earth and a large asteroid resulted in massive damage and generated enough heat to cause irreversible changes in
Earth's atmosphere.
F.There was a particularly large mass extinction that occurred around 250 million years ago at the end of the Permian period, whose cause could not be determined.
托福阅读答案
1.以mass extinctions做关键词定位至第一句，说大量生物在短时间内灭绝的这种现象叫做大灭绝事件，C是原文的同义替换，所以是正确答案。70 million 和250 million是两次大灭绝事件发生的时间，不是A说的七千万年一直在发生，也不是D说的每2500万年发生一次；B的began和原文的end是反的，错。
2.以at present做关键词定位至最后一句，但这段很短，快速扫完后两句之后就有答案，说现代生物灭绝的速度和大灭绝的时候差不多，得出大灭绝现在正在发生，所以原因是灭绝速度相似，答案A。
3.extend延伸，延长，extended长期的，所以long是正确答案,选D。原句说其他机制可能会渐渐发生，在一个什么样的时期内，既然是渐渐发生，当然需要比较长的时间，所以答案是D。虽然长但不是无限，所以unlimited错；specific 特定时间和reasonable合理时间原文都没说。
4.EXCEPT题，本段第一句就问了原因第二句就开始回答，所以这道题正选比较好。第二句的warming or cooling对应D答案，正确，不选；changing position 对应B答案，正确，不选；最后一句的habitat destruction对应A答案，正确，
不选；只有C没有对应，所以C错，选。
5.问全段的，最好用排除法。A的exact causes做关键词定位至前两句，原文说有很多假设，所以没有准确原因，A错；B的future原文没说，所以错；C的一大堆生物做关键词定位至第三句，但原文没说它们是最先遭殃的一群生物，C 错；D的land and seas做关键词定位至倒数第三句，simultaneously就是at the same time，正确。
6.原句说这两个人认为mass extinction是重复出现的。正确答案是A，C和D 的错误很容易分辨，因为C和D的谓语动词increase是原文没说到的，所以C 和D都错。B项颇具迷惑性，但B错在将suggest和study两个动词并列在一起，但原句是先study，之后才suggest，虽然没有明确指出A的base on，但先有研究后有结论，这个结论当然与研究有关，所以A正确。
7.以companion star hypothesis做关键词定位至最后一句，说mass extinction的反复发生支持了companion star hypothesis，这个hypothesis 说轨道变形导致一些星体偏离正常轨道，成为陨星掉入地球，原句说屡次发生，所以能够解释extinction的频率，答案是B。
8.account for负责，解释，所以正确答案是explain，选C。原句说在所有试图什么晚白垩世生物大灭绝事件的假说当中，陨星撞击说是最吸引人的。运行撞击能够怎么样生物灭绝，A的challenge和D的test意思相似，二者是解释关系，不是反驳或者测试彼此，所以两个答案都不对，而陨星撞击更不是简单描述晚白垩世生物灭绝，所以describe不对，A错。
9.以人名做关键词定位至第一句，但第一句没说为什么铱测试对验证A的假说很有用，往下看，说地球上Ir几乎没有，但其他星体含量多很多，同义改写的答案
是B。也就是说如果地球上发现大量Ir，就说明遭受过撞击，选B。
10.修辞目的题，看本句先，原句说Ir异常支持了撞击说，但还没发现具体的星体。所以B说没有evidence，错，说反了；C有人reject他的观点，还有D的scientists的责任原文都没说，不选；正确答案是A，只有Ir异常这个间接证据就可以支持撞击说，所以是indirect evidence。
11.intense高强度的，密集的，极端的，所以D的extreme正确。原句说撞击产生的什么样的热量可以产生出很多的heat-shocked石英，都heat shocked 了，肯定是heat很大很多，而sudden和immediate都表示时间概念不表示多少所以A,C都错；B的unusual虽然可能表示多，但不一定，也有可能表示时间概念，错。
12.问整段的题关注头尾，开头说撞击会留下大坑，又说热量blabla，结尾说某某地方被认为是撞击发生的地方，所以应该是支持撞击理论，所以B的additional supporting evidence正确；D的doubts不对；C说撞击位置很难找到与最后一句相反，错；A的test原文没说。
13.两个过渡点，分别是代词these和名称two extinctions，根据two extinctions可以确定B或者D是答案，因为C前后在叙述两词extinction，一定不能插入任何句子；但these说明待插入句必须放后，所以D正确。
14.Astroid选项对应整个第三段，A正确。
Researchers选项对应原文第四段最后一句，B正确。
According选项是第六段的一个细节，C不选。
The unusual选项对应原文第七段的前两句，D正确。
The collision选项中的irreversible与原文说反，原文第五段说particles settle
之后大气层就会复原，而不是不可逆转，E不选。There was选项是第一段中的一个细节，F不选。