Official5托福阅读Passage3 The Cambrian Explosion文本+题目原文+答案解析【雷哥托福】2019-01-16 18:21:50 发布 来源：雷哥托福 阅读量:4566
TPO5托福阅读Passage3 The Cambrian Explosion文本+题目原文+答案解析
The Cambrian Explosion
The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4.6 billion years ago, the origin of life about 3.5 billion years ago, the origin of eukaryotic life-forms (living things that have cells with true nuclei) about 1.5 billion years ago, and the origin of animals about 0.6 billion years ago. The last event marks the beginning of the Cambrian period. Animals originated relatively late in the history of Earth—in only the last 10 percent of Earth’s history. During a geologically brief 100-million-year period, all modern animal groups (along with other animals that are now extinct) evolved. This rapid origin and diversification of animals is often referred to as “the Cambrian explosion.”
Scientists have asked important questions about this explosion for more than a century. Why did it occur so late in the history of Earth? The origin of multicellular forms of life seems a relatively simple step compared to the origin of life itself. Why does the fossil record not document the series of evolutionary changes during the evolution of animals? Why did animal life evolve so quickly? Paleontologists continue to search the fossil record for answers to these questions.
One interpretation regarding the absence of fossils during this important 100-million-year period is that early animals were soft bodied and simply did not fossilize. [■]Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur. [■]Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition.[■]In fact, fossil beds containing soft-bodied animals have been known for many years.[■]
The Ediacara fossil formation, which contains the oldest known animal fossils, consists exclusively of soft-bodied forms. Although named after a site in Australia, the Ediacara formation is worldwide in distribution and dates to Precambrian times. This 700-million-year-old formation gives few clues to the origins of modern animals, however, because paleontologists believe it represents an evolutionary experiment that failed. It contains no ancestors of modern animal groups.
A slightly younger fossil formation containing animal remains is the Tommotian formation, named after a locale in Russia. It dates to the very early Cambrian period, and it also contains only soft-bodied forms. At one time, the animals present in these fossil beds were assigned to various modern animal groups, but most paleontologists now agree that all Tommotian fossils represent unique body forms that arose in the early Cambrian period and disappeared before the end of the period, leaving no descendants in modern animal groups.
A third fossil formation containing both soft-bodied and hard-bodied animals provides evidence of the result of the Cambrian explosion. This fossil formation, called the Burgess Shale, is in Yoho National Park in the Canadian Rocky Mountains of British Columbia. Shortly after the Cambrian explosion, mud slides rapidly buried thousands of marine animals under conditions that favored fossilization. These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups. These unassignable animals include a large swimming predator called Anomalocaris and a soft-bodied animal called Wiwaxia, which ate detritus or algae. The Burgess Shale formation also has fossils of many extinct representatives of modern animal groups. For example, a well-known Burgess Shale animal called Sidneyia is a representative of a previously unknown group of arthropods (a category of animals that includes insects, spiders, mites, and crabs).
Fossil formations like the Burgess Shale show that evolution cannot always be thought of as a slow progression. The Cambrian explosion involved rapid evolutionary diversification, followed by the extinction of many unique animals. Why was this evolution so rapid? No one really knows. Many zoologists believe that it was because so many ecological niches were available with virtually no competition from existing species. Will zoologists ever know the evolutionary sequences in theCambrian explosion? Perhaps another ancient fossil bed of soft-bodied animals from 600-million-year-old seas is awaiting discovery.
TPO5托福阅读Passage3The Cambrian Explosion题目
Question 1 of 14：The word “significant ” in the passage is closest in meaning to
Question 2 of 14：The word “relatively ” in the passage is closest in meaning to
Question 3 of 14:The word “diversification ” in the passage is closest in meaning to
A. emergence of many varieties
B. steady decline in number
C. gradual increase in body size
D. sudden disappearance
Question 4 of 14：The period discussed in the passage is referred to as an “explosion ” because it
A. occurred 0.6 billion years ago, late in Earth’s history
B. was characterized by the unusually fast evolution of many new life-forms
C. was characterized by widespread animal extinction
D. was characterized by violent volcanic eruptions
Question 5 of 14：According to Paragraph2, which of the following is NOT a question that paleontologists asked about the Cambrian explosion?
A. Why was the origin of life a simple step in Earth’s history?
B. Why did it take so long for multicellular organisms to develop?
C. Why did animal life evolve so rapidly?
D. Why does the fossil record lack evidence of animal evolution during that time?
Question 6 of 14：Which of the following best describes the relationship between paragraph 2 and paragraph 3?
A. Paragraph 2 puts forward several scientific claims, one of which is rejected in paragraph 3.
B. Paragraph 2 poses several questions, and paragraph 3 offers a possible answer to one of them.
C. Paragraph 2 presents outdated traditional views, while paragraph 3 presents the current scientific conclusions
.D. Paragraph 2 introduces a generalization that is illustrated by specific examples in paragraph 3.
Question 7 of 14：The word “promote ” in the passage is closest in meaning to
Question 8 of 14：Which of the following is NOT mentioned in paragraph 4 as being true of the Ediacara formation?
A. It contains fossils that date back to the Precambrian period.
B. It contains only soft-bodied animal fossils.
C. It is located on a single site in Australia.
D. It does not contain any fossils of the ancestors of modern animals.
Question 9 of 14：Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A. The animals found in the Tommotian fossil bed were once thought to belong to a variety of modern animal groups, but now they are thought to have descended from a single group.
B. Animals in the Tommotian fossil beds were initially assigned to modern animal groups but are now thought to belong to groups that emerged and died out during the Cambrian period.
C. Though at first they thought otherwise, paleontologists now agree that the animals in the Tommotian have body forms from which modern animals have descended.
D. It is unclear whether the Tommotian fossils from the early Cambrian period represent unique body forms or whether they should be assigned to various modern animal groups.
Question 10 of 14：Why does the author mention “Anomalocaris” and “Wiwaxia”?
A. To contrast predators with animals that eat plants such as algae
B. To question the effects of rapid mud slides on fossilization
C. To suggest that much is still unknown about animals found in the Burgess Shale
D. To provide examples of fossils that cannot be assigned to a modern animal group
Question 11 of 14：“Sidneyia ” is an example of
A. a relative of Anomalocaris and Wiwaxia
B. a previously unknown Burgess Shale animal
C. an extinct member of a currently existing category of animals
D. an animal that cannot be assigned to any modern animal group
Question 12 of 14：What can be inferred from paragraph 7 about why the Cambrian explosion is so unusual?
A. It generated new ecological niches through the extinction of many unique animals.
B. It was a period of rapid evolution, and evolution is often thought of as a slow process.
C. It is a period whose evolutionary sequences are clearly marked.
D. It generated a very large number of ancient fossil beds containing soft-bodied animals.
Question 13 of 14：Look at the four squares [■] that indicate where the following sentence could be added to the passage.Where could the sentence best fit?
It is relatively rare because the fossilization of soft-bodied animals requires a special environment..
A. Fossilization of soft-bodied animals is less likely than fossilization of hard-bodied animals, but it does occur.
B. Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition.
C. In fact, fossil beds containing soft-bodied animals have been known for many years.
Question 14 of 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 answer choices 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.
The term “Cambrian explosion” refers to the geologically brief period during which all modern animal groups evolved.
A.Little is known about the stages of evolution during the Cambrian period, in part because early animals were soft bodied and could fossilize only under particular conditions.
B.While animal fossils from before the Cambrian explosion have no modern descendants, many animals that evolved during the Cambrian explosion can be assigned to modern groups.
C.The Cambrian period is significant because it marks the emergence of eukaryotic life-forms—organisms that have cells with true nuclei.
D.The Ediacara fossil formation provides the most information about the Cambrian explosion, while the earlier, Tommotian and Burgess Shale formations give clues about Precambrian evolution.
E.Zoologists are awaiting the discovery of a 600-million-year-old fossil formation in order to be able to form a theory of how animal evolution progressed.
F. Although the reasons for the rapid evolution of animals during the Cambrian period are not known, one proposed explanation is an abundance of niches with a lack of competitors.
TPO5托福阅读Passage3The Cambrian Explosion解析
Question 1 of 14
Question 2 of 14
题目解析：relatively: 相对地。A是令人意外地;B是共同地;C是相对地;D是典型地。所以comparatively相对地正确。对应原文：Animals originated relatively late in the history of Earth—in only the last 10 percent of Earth’s history.原句relatively late之后有个破折号对这个进行了解释，说地球历史的最后10%，当然是相对靠后的。A吃惊B聚集D有特点都不对。
Question 3 of 14
题目解析：diversification: 分化。想到diverse多样，所以A出现了很多变体正确。对应原文：This rapid origin and diversification of animals is often referred to as “the Cambrian explosion.”原文与之并列的是origin(起源)，带有出现的意思，所以emergence对得上;B的decline和D的disappear都说反了;C的body size与原文无关。
Question 4 of 14
题目解析：以explosion做关键词定位至第一段最后一句，注意这道题的相关信息不在第二段而是在第一段。说rapid origin and diversification所以叫explosion，所以B正确。A的时间不能作为explosion的依据;C灭绝说反了;D火山爆发没说。
Question 5 of 14
题目解析：A EXCEPT题，排除法。A的simple step做关键词定位至第三句，但这句话不是一个问题，所以A错，选;B选项的so long对应原文第二句的so late，所以正确，不选，注意不要单纯以multicellular organism做关键词，会导致定位错误;C对应倒数第二句，正确，不选;D的lack evidence对应原文倒数第三句的not document，正确，不选
Question 6 of 14
Question 7 of 14
题目解析：promote: 促进，提升。所以C的encourage正确。A是使…复杂;B是防止;D是影响。对应原文：Conditions that promote fossilization of soft-bodied animals include very rapid covering by sediments that create an environment that discourages decomposition.原文的condition应该是对fossilization起到正面的作用，B的prevent和D的affect都是负面作用，所以都不对;complicate是使变复杂，原文没有给出相关信息，错。
Question 8 of 14
题目解析：A的Precambrian对应第二句，正确，不选;C的相关信息也来自第二句，但第二句说的是worldwide in distribution，不是只在澳大利亚有，所以C说反了，选：
Question 9 of 14
Question 10 of 14
题目解析：Anomalocaris和Wiwaxia是两种unassignable动物的例子，往前看：These fossil beds provide evidence of about 32 modern animal groups, plus about 20 other animal body forms that are so different from any modern animals that they cannot be assigned to any one of the modern groups.前句很清楚说有些动物是不能被分在任何一个group里，接着就给了这两种作为例子，所以D正确，其他都没说。
Question 11 of 14
Question 12 of 14
题目解析：以Cambrian Explosion做关键词定位至第二句，注意倒数第二句也有一个Cambrian Explosion，但因为与问题无关，所以不读。本句说寒武纪大爆发包含了很多动物的快速出现然后快速灭亡，接着提出问题为什么这么快并给出解答。所以问题中的unusual就是说快的不正常，所以答案B正确。A的new ecological niches原文没有相关信息;C原文只是一个问题，C变成了答案，不对;D错，原文最后一句说一个bed，不是很多beds，而且是awaiting discovery，不是已经发现了。
Question 13 of 14
题目解析：两个过渡点，fossilization of soft-bodied animals和special environment，凭第一个A/B/C都有可能，但special environment说明A不对，而且应该先说需要一个特殊的环境然后再说这个环境是什么，而不是反过来。何况B点之后的condition和插入句中的environment刚好对应。
Question 14 of 14
题目解析：little选项对应原文第三段第一句，正确。while选项对应原文第五段最后一句和第一段倒数第二句，正确。the Cambrian选项把原文的两个不相干的概念杂糅到一起，胡编乱造，不选。the Edicara选项对应第四段第一句，但因为第四段整个是个例子，所以这个是细节，不选。zoologist选项对应第七段最后一句，但是是细节，不选。although选项对应原文第七段倒数第三句，正确。