TPO20托福阅读Passage3 Fossol preservation文本+题目原文+答案解析

Fossol preservation

When one considers the many ways by which organisms are completely destroyed after death, it is remarkable that fossils are as common as they are. Attack by scavengers and bacteria, chemical decay, and destruction by erosion and other geologic agencies make the odds against preservation very high. However, the chances of escaping complete destruction are vastly improved if the organism happens to have a mineralized skeleton and dies in a place where it can be quickly buried by sediment. Both of these conditions are often found on the ocean floors, where shelled invertebrates (organisms without spines) flourish and are covered by the continuous rain of sedimentary particles. Although most fossils are found in marine sedimentary rocks, they also are found in terrestrial deposits left by streams and lakes. On occasion, animals and plants have been preserved after becoming immersed in tar or quicksand, trapped in ice or lave flows, or engulfed by rapid falls of volcanic ash.

The term “fossil” often implies petrifaction, literally a transformation into stone. After the death of an organism, the soft tissue is ordinarily consumed by scavengers and bacteria. They empty shell of a snail or clam may be left behind, and if it is sufficiently durable and resistant to dissolution, it may remain basically unchanged for a long period of time. Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old. In many marine creatures, however, the skeleton is composed of mineral variety of calcium carbonate called aragonite. Although aragonite has the same composition as the more familiar mineral known as calcite, it has a different crystal form, is relatively unstable, and in time changes to the more stable calcite.

Many other processes may after the shell of the clam or snail and enhance its chances for preservation. Water containing dissolved silica, calcium carbonate, or iron many circulate through the enclosing sediment and be deposited in cavities such as narrow cavities and canals in bone once occupied by blood vessels and nerves. In such cases, the original composition of the bone or shell remains, but the fossil is made harder and more durable. This addition of a chemically precipitated substance into precipitated is termed “permineralization.”

Petrifaction may also involve a simultaneous exchange of the original substance of a dead plant or animal with mineral matter of a different composition. This process is termed “replacement” because solutions have dissolved the original material and replaced it with an equal volume of the new substance. Replacement can be a marvelously precise process, so that details of shell ornamentation, tree rings in wood, and delicate structures in bone are accurately preserved.

■Another type of fossilization, known as carbonization, occurs when soft tissues are preserved as thin film of carbon.■ Leaves and tissue of soft-bodied organisms such as jellyfish or worms may accumulate, become buried and compressed, and lose their volatile constituents.■ The carbon often remains behind as a blackened silhouette.■

Although it is certainly true that the possession of hard parts enhances the prospect of preservation, organisms having soft tissues and organs are also occasionally preserved. Insects and even small invertebrates have been found preserved in the hardened resins of conifers and certain other trees. X-ray examination of thin slabs of roc sometimes reveals the ghostly outlines of tentacles, digestive tracts, and visual organs of a variety of marine creatures. Soft parts, including skin, hair, and viscera of ice age mammoths, have been preserved in frozen soil or in the oozing tar of oil seeps.

The probability that actual remains of soft tissue will be preserved is improved if the organism dies in an environment of rapid deposition and oxygen deprivation. Under such conditions, the destructive effects of bacteria are diminished. The middle Eocene Messel shale (from about 48 million years ago) of German accumulated in such an environment. The shale was deposited in an oxygen-deficient lake where lethal gases sometimes bubbled up and killed animals. Their remains accumulated on the floor of the lake and were then covered by clay and silt. Among the superbly preserved Messel fossils are insects with iridescent exoskeletons (hard outer coverings), frogs with skin and blood vessels intact, and even entire small mammals with preserved fur and soft tissue.

TPO20 托福阅读 Passage3 Fossol preservation 题目

Question 1 of 14:  The word “agencies” in the passage is closest in meaning to

A. Combinations

B. Problems

C. Forces

D. Changes

Question 2 of 14: In paragraph 1, what is the author’s purpose in providing examples of how organisms are destroyed?

A. To emphasize how surprising it is that so many fossils exist

B. To introduce a new geologic theory of fossil preservation

C. To explain why the fossil record until now has remained incomplete

D. To compare how fossils form on land and in water

Question 3 of 14: The word “terrestrial” in the passage is closest in meaning to

A. Land

B. Protected

C. Alternative

D. Similar

Question 4 of 14:  Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

Incorrect choices change in the meaning in important ways or leave out essential information.

A .When snail or clam shells are left behind, they must be empty in order to remain durable and resist dissolution.

B .Although snail and clam shells are durable and resist dissolving, over time they slowly begin to change.

C. Although the soft parts of snails or clams dissolve quickly, their hard shells resist dissolution for a long time.

D .Empty snail or clam shells that are strong enough not to dissolve may stay in their original state for a long time.

Question 5 of 14: Why does the author mention “aragonite” in the passage?

A. To emphasize that some fossils remain unaltered for millions of years.

B. To contrast fossil formation in organisms with soft tissue and in organisms with hard shells

C. To explain that some marine organisms must undergo chemical changes in order to fossilize

D. To explain why fossil shells are more likely to survive than are fossil skeletons.

Question 6 of 14:  The word “enhance” in the passage is closest in meaning to

A. Control

B. Limit

C. Combine

D. Increase

Question 7 of 14: Which of the following best explains the process of permineralization mentioned in paragraph 3?

A. Water containing calcium carbonate circulates through a shell and deposits sediment.

B. Liquid containing chemicals hardens an already existing fossil structure.

C. Water passes through sediment surrounding a fossil and removes its chemical content.

D. A chemical substance enters a fossil and changes its shape.

Question 8 of 14:  The word “precise” in the passage is closest in meaning to

A. Complex

B. Quick

C. Exact

D. Reliable

Question 9 of 14: Paragraph 5 suggests which of the following about the carbonization process?

A. It is completed soon after an organism dies.

B. It does not occur in hard-shell organisms.

C. It sometimes allows soft-tissued organisms to be preserved with all their parts.

D. It is a more precise process of preservation than is replacement.

Question10 of 14: The word “prospect” in the passage is closest in meaning to

A. Completion

B. Variety

C. Possibility

D. Speed

Question11 of 14: According to paragraph 7, how do environments containing oxygen affect fossil preservation?

A. They increase the probability that soft-tissued organisms will become fossils.

B. They lead to more bacteria production.

C. They slow the rate at which clay and silt are deposited.

D. They reduce the chance that animal remains will be preserved.

Question 12 of 14: According to the passage, all of the following assist preservation EXCEPT

A. The presence of calcite in an organism’s skeleton

B. The presence of large open areas along an ocean floor

C. The deposition of a fossil n sticky substances such as sap or tar

D. The rapid burial of an organism under layers of silt

Question13 of 14: Look at the four squares that indicate where the following sentence can be added to the passage. Where would the sentence best fit?

But the evidence of past organic life is not limited to petrifaction.

A. Another type of fossilization, known as carbonization, occurs when soft tissues are preserved as thin film of carbon.

B. Leaves and tissue of soft-bodied organisms such as jellyfish or worms may accumulate, become buried and compressed, and lose their volatile constituents.

C. The carbon often remains behind as a blackened silhouette.

D. /

Question14 of 14: The remains of ancient life are amazingly well preserved in the form of fossils.

Answer choices

A. Environmental characteristics like those present on ocean floors increase the likelihood that plant and animal fossils will occur.

B .Fossils are more likely to the preserved in shale deposits than in deposits of clay and silt.

C .The shells of organisms can be preserved by processes of chemical precipitation or mineral exchange.

D. Freezing enables the soft parts of organisms to survive longer than the hard parts.

E. Comparatively few fossils are found in the terrestrial deposits of streams and lakes.

F. Thin films of carbon may remain as an indication of soft tissue or actual tissue may be preserved if exposure to bacteria is limited.

TPO20托福阅读Passage3Fossol preservation真题解析

Question 1 of 14

正确答案：C

解析：agency“代理，中介，作用”，所以答案是force。原句提到由于腐食动物和细菌的侵袭，化学侵蚀和其他地质的作用，使得保存的难度非常大。combination“组合”明显不合文意，problem是个负向词，不合文意，之前并列的都不是变化，change不正确。

Question 2 of 14

正确答案：A

解析：所在句是一个例子，所以往前看，前一句提到fossil遭破坏的方式和fossil一样多，后面就提到很多破坏的方式，所以答案是A，阐释为什么如此多破坏之下还有这么多化石存在。

Question 3 of 14

正确答案：A

解析：terrestrial“陆地的，陆生的”，所以正确答案是A。原文提到尽管大部分的化石都是在海洋中找到的，但也有一些是在河湖中的沉积物当中找到的，既然前文都提到了大部分是在海洋里找到的，后面推测后面会说是在陆地上找到的，所以答案是terrestrial，B、C、D都不合文意。

Question 4 of 14

正确答案：D

解析：原句的结构是并列加条件，意思是可能会留下蜗牛或蛤蜊空壳，如果空壳足够坚固并且能抵御分解，就有可能在很长一段时间内基本上保持原样。所以正确答案是D。A的must be empty原文未提及；B和C的关系都错误；D说的是shell会被剩下，如果足够耐腐蚀，就能保存一段时间。

Question 5 of 14

正确答案：C

解析：该句的前一句说一亿年前的沉积物中能发现骨骼不变的海生无脊椎动物，与A相符，但A本身不是一个观点，所以A不正确；B和D完全未提及，不正确；强调的中心在例子所在句的下一句，提到aragonite的晶体形状不同，相对不那么稳定，会变成更稳定的形式，所以答案是C，想稳定的话必须再变。

Question 6 of 14

正确答案：D

解析：enhance“提升，提高”，所以正确答案是D的increase。原文提到很多化学过程都能改变壳体的结构并且怎么样它们作为化石保留下来的机会，combine明显不合文意；limit和control意思相近，而且这两个词与increase意思相反。这里答案选D。

Question 7 of 14

正确答案：B

解析：以permineralization做关键词定位至最后一句。提到将chemically precipitate的物质加入precipitate的过程叫做permineralization，this指代前文，所以往前看，前面提到血管和神经占据的空隙会被充填，骨头和壳体会留下来，变得更坚固，所以答案是B。A的“包含”calcium不全面，而且原文的变硬也未提及；C的remove chemical content和D的change shape都没提到。

Question 8 of 14

正确答案：C

解析：precise“精确的”，所以C的exact正确。原文提到replacement是一个非常什么样的过程，壳体的纹饰，树轮和骨架上的微细结构都被记录下来，B“快”和D“可信”完全不合文意，细微结构被记录下来不见得复杂，所以complex也不正确。

Question 9 of 14

正确答案：B

解析：此题可以采用排除法，A错误，原文提到生命死后要经过若干过程才会carbonization，所以A的soon明显错误；B正确，原文明确指出carbonization发生在柔软组织中，当然也就不会发生在硬壳动物身上；C的all their parts和D的比较原文都未提及，都错误。

Question 10 of 14

正确答案：C

解析：prospect“展望，前景”，所以C意思最为接近。原句提到尽管有硬壳提高了保存下来的什么，但软体动物也能偶尔被保存下来。根据让步推出硬壳动物应该是容易保存下来，但跟保存下来的完整性和种类都无关，所以variety和completion都不正确，speed完全不合文意。

Question 11 of 14

正确答案：D

解析：以oxygen做关键词定位至第一句，提到如果快速埋藏，并且在缺氧环境下，化石保存的概率会增加，也就是说氧的存在不利于化石的保存，所以正确答案是D，A与D刚好完全相反，所以A错误，也说明两个相反的有一个对；C完全未提及；B错误，原文提到缺氧能减轻细菌的破坏作用，但并不意味着有氧细菌就会变多，所以B未提及。

Question 12 of 14

正确答案：B

解析：此题可以采用排除法，由于考查全文，应该关注各段开头。A的skeleton和calcite做关键词定位至第六段首句，正确，不选；B的ocean floor在原文中虽然有出现，但open areas没有，所以B错误，选；C的sap or tar做关键词定位至第六段最后一句，正确，不选；D的rapid burial和layer of silt做关键词定位至第七段第一句，正确，不选。

Question 13 of 14

正确答案：A

解析：这道题如果找名词过渡，最容易找的应该是petrification，但整段中既没有petrification，也没有同义词替换，这段段首已经开始提到carbonization，也就是说petrification应该是上一段或者下一段说的，也就是A或者D正确，但待插入句说不仅限于，也就是前面已经说过petrification了，所以A正确D错误。

Question 14 of 14

正确答案：ACF

解析：A选项对应原文首段第三句，正确；B选项的比较原文未提及，属于无中生有，故错误；C选项对应原文第三段最后一句和第四段开头，选项是一个总结，正确；D选项在原文第六段结尾提了一下，但并没说软的部分会存的更长时间一些，不选；E选项对应在原文第一段的最后两句话，文中说的是大部分都是在沉积岩中发现的，所以选项中Comparatively few明显错误了，不选；F选项对应原文第五段和第七段开头，与原文描述一致，正确。故答案为ACF。

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