托福阅读――考古类(六).pdf

智 课 网 托 福 备 考 资 料托福阅读考古类（六）When one considers the many ways by which organisms arecompletely destroyed after death,it is remarkable that fossils areas common as they are.Attack by scavengers and bacteria,chemical decay,and destruction by erosion and other geologicagencies make the odds against preservation very high.However,the chances of escaping complete destruction are vastlyimproved if the organism happens to have a mineralizedskeleton and dies in a place where it can be quickly buried bysediment.Both of these conditions are often found on the oceanfloors,where shelled invertebrates(organisms without spines)flourish and are covered by the continuous rain of sedimentaryparticles.Although most fossils are found in marine sedimentaryrocks,they also are found in terrestrial deposits left by streamsand lakes.On occasion,animals and plants have been preservedafter becoming immersed in tar or quicksand,trapped in ice orlava flows,or engulfed by rapid falls of volcanic ash.The term fossil often implies petrifaction,literally atransformation into stone.After the death of an organism,thesoft tissue is ordinarily consumed by scavengers and bacteria.The empty shell of a snail or clam may be left behind,and if it issufficiently durable and resistant to dissolution,it may remainbasically unchanged for a long period of time.Indeed,unalteredshells of marine invertebrates are known from deposits over 100million years old.In many marine creatures,however,theskeleton is composed of a mineral variety of calcium carbonatecalled aragonite.Although aragonite has the same compositionas the more familiar mineral known as calcite,it has a differentcrystal form,is relatively unstable,and in time changes to themore stable calcite.Many other processes may alter the shell of a clam or snailand enhance its chances for preservation.Water containingdissolved silica,calcium carbonate,or iron may circulate throughthe enclosing sediment and be deposited in cavities such asmarrow cavities and canals in bone once occupied by bloodvessels and nerves.In such cases,the original composition of thebone or shell remains,but the fossil is made harder and moredurable.This addition of a chemically precipitated substance intopore spaces is termed permineralization.Petrifaction may also involve a simultaneous exchange of theoriginal substance of a dead plant or animal with mineral matterof a different composition.This process is termed replacementbecause solutions have dissolved the original material andreplaced it with an equal volume of the new substance.Replacement can be a marvelously precise process,so thatdetails of shell ornamentation,tree rings in wood,and delicatestructures in bone are accurately preserved.Another type of fossilization,known as carbonization,occurswhen soft tissues are preserved as thin films of carbon.Leavesand tissue of soft-bodied organisms such as jellyfish or wormsmay accumulate,become buried and compressed,and lose theirvolatile constituents.The carbon often remains behind as ablackened silhouette.Although it is certainly true that the possession of hard partsenhances the prospect of preservation,organisms having softtissues and organs are also occasionally preserved.Insects andeven small invertebrates have been found preserved in thehardened resins of conifers and certain other trees.X-rayexamination of thin slabs of rock sometimes reveals the ghostlyoutlines of tentacles,digestive tracts,and visual organs of avariety of marine creatures.Soft parts,including skin,hair,andviscera of ice age mammoths,have been preserved in frozen soilor in the oozing tar of oil seeps.The probability that actual remains of soft tissue will bepreserved is improved if the organism dies in an environment ofrapid deposition and oxygen deprivation.Under such conditions,the destructive effects of bacteria are diminished.The MiddleEocene Messel Shale(from about 48 million years ago)ofGermany accumulated in such an environment.The shale wasdeposited in an oxygen-deficient lake where lethal gasessometimes bubbled up and killed animals.Their remainsaccumulated on the floor of the lake and were then covered byclay and silt.Among the superbly preserved Messel fossils areinsects with iridescent exoskeletons(hard outer coverings),frogswith skin and blood vessels intact,and even entire smallmammals with preserved fur and soft tissue.Paragraph 1:When one considers the many ways by whichorganisms are completely destroyed after death,it is remarkablethat fossils are as common as they are.Attack by scavengers andbacteria,chemical decay,and destruction by erosion and othergeologic agencies make the odds against preservation very high.However,the chances of escaping complete destruction arevastly improved if the organism happens to have a mineralizedskeleton and dies in a place where it can be quickly buried bysediment.Both of these conditions are often found on the oceanfloors,where shelled invertebrates(organisms without spines)flourish and are covered by the continuous rain of sedimentaryparticles.Although most fossils are found in marine sedimentaryrocks,they also are found in terrestrial deposits left by streamsand lakes.On occasion,animals and plants have been preservedafter becoming immersed in tar or quicksand,trapped in ice orlava flows,or engulfed by rapid falls of volcanic ash.1.The word agencies in the passage is closest in meaningtoO combinationsO problemsO forcesO changes2.In paragraph 1,what is the authors purpose in providingexamples of how organisms are destroyed?O To emphasize how surprising it is that so many fossils existO To introduce a new geologic theory of fossil preservationO To explain why the fossil record until now has remainedincompleteO To compare how fossils form on land and in water3.The word terrestrial in the passage is closest in meaningtoO landO protectedO alternativeO similarParagraph 2:The term fossil often implies petrifaction,literally a transformation into stone.After the death of anorganism,the soft tissue is ordinarily consumed by scavengersand bacteria.The empty shell of a snail or clam may be leftbehind,and if it is sufficiently durable and resistant todissolution,it may remain basically unchanged for a long periodof time.Indeed,unaltered shells of marine invertebrates areknown from deposits over 100 million years old.In many marinecreatures,however,the skeleton is composed of a mineral varietyof calcium carbonate called aragonite.Although aragonite hasthe same composition as the more familiar mineral known ascalcite,it has a different crystal form,is relatively unstable,and intime changes to the more stable calcite.4.Which of the sentences below best expresses the essentialinformation in the highlighted sentence in the passage?Incorrectchoices change the meaning in important ways or leave outessential informationO When snail or clam shells are left behind,they must beempty in order to remain durable and resist dissolution.O Although snail and clam shells are durable and resistdissolving,over time they slowly begin to change.O Although the soft parts of snails or clams dissolve quickly,their hard shells resist dissolution for a long time.O Empty snail or clam shells that are strong enough not todissolve may stay in their original state for a long time.5.Why does the author mention aragonite in the passage?O To emphasize that some fossils remain unaltered formillions of yearsO To contrast fossil formation in organisms with soft tissueand in organisms with hard shellsO To explain that some marine organisms must undergochemical changes in order to fossilizeO To explain why fossil shells are more likely to survive thanare fossil skeletonsParagraph 3:Many other processes may after the shell of aclam or snail and enhance its chances for preservation.Watercontaining dissolved silica,calcium carbonate,or iron maycirculate through the enclosing sediment and be deposited incavities such as marrow cavities and canals in bone onceoccupied by blood vessels and nerves.In such cases,the originalcomposition of the bone or shell remains,but the fossil is madeharder and more durable.This addition of a chemicallyprecipitated substance into pore spaces is termedpermineralization.6.The word enhance in the passage is closest in meaningtoO controlO limitO combineO increase7.Which of the following best explains the process ofpermineralization mentioned in paragraph 3?O Water containing calcium carbonate circulates through ashell and deposits sediment.O Liquid containing chemicals hardens an already existingfossil structure.O Water passes through sediment surrounding a fossil andremoves its chemical content.O A chemical substance enters a fossil and changes itsshape.Paragraph 4:Petrifaction may also involve a simultaneousexchange of the original substance of a dead plant or animalwith mineral matter of a different composition.This process istermed replacement because solutions have dissolved theoriginal material and replaced it with an equal volume of the newsubstance.Replacement can be a marvelously precise process,sothat details of shell ornamentation,tree rings in wood,anddelicate structures in bone are accurately preserved.8.The word precise in the passage is closest in meaning toO complexO quickO exactO reliableParagraph 5:Another type of fossilization,known ascarbonization,occurs when soft tissues are preserved as thinfilms of carbon.Leaves and tissue of soft-bodied organisms suchas jellyfish or worms may accumulate,become buried andcompressed,and lose their volatile constituents.The carbonoften remains behind as a blackened silhouette.9.Paragraph 5 suggests which of the following about thecarbonization process?O It is completed soon after an organism dies.O It does not occur in hard-shell organisms.O It sometimes allows soft-tissued organisms to bepreserved with all their parts.O It is a more precise process of preservation than isreplacement.Paragraph 6:Although it is certainly true that the possessionof hard parts enhances the prospect of preservation,organismshaving soft tissues and organs are also occasionally preserved.Insects and even small invertebrates have been found preservedin the hardened resins of conifers and certain other trees.X-rayexamination of thin slabs of rock sometimes reveals the ghostlyoutlines of tentacles,digestive tracts,and visual organs of avariety of marine creatures.Soft parts,including skin,hair,andviscera of ice age mammoths,have been preserved in frozen soilor in the oozing tar of oil seeps.10.The word prospect in the passage is closest in meaningtoO completionO varietyO possibilityO speedParagraph 7:The probability that actual remains of softtissue will be preserved is improved if the organism dies in anenvironment of rapid deposition and oxygen deprivation.Undersuch conditions,the destructive effects of bacteria arediminished.The Middle Eocene Messel Shale(from about 48million years ago)of Germany accumulated in such anenvironment.The shale was deposited in an oxygen-deficientlake where lethal gases sometimes bubbled up and killedanimals.Their remains accumulated on the floor of the lake andwere then covered by clay and silt.Among the superblypreserved 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 softtissue.11.According to paragraph 7,how do environmentscontaining oxygen affect fossil preservation?O They increase the probability that soft-tissued organismswill become fossils.O They lead to more bacteria production.O They slow the rate at which clay and silt are deposited.O They reduce the chance that animal remains will bepreserved.12.According to the passage,all of the following assist infossil preservation EXCEPTO the presence of calcite in an organisms skeletonO the presence of large open areas along an ocean floorO the deposition of a fossil in sticky substances such as sapor tarO the rapid burial of an organism under layers of siltAnother type of fossilization,known as carbonization,occurs when soft tissues are preserved as thin films of carbon.Leaves and tissue of soft-bodied organisms such as jellyfish orworms may accumulate,become buried and compressed,andlose their volatile constituents.The carbon often remainsbehind as a blackened silhouette.13.Look at the four squares that indicate where thefollowing sentence can be added to the passage.But the evidence of past organic life is not limited topetrifaction.Where would the sentence best fit?Click on a square to insert the sentence in the passage.14.Directions:An introductory sentence for a brief summaryof the passage is provided below.Complete the summary byselecting the THREE answer choices that express the mostimportant ideas in the passage.Some answer choices do notbelong in the summary because they express ideas that are notpresented in the passage or are minor ideas in the passage.Thisquestion is worth 2 points.The remains of ancient life are amazingly well preserved inthe form of fossils.Answer ChoicesO Environmental characteristics like those present on oceanfloors increase the likelihood that plant and animal fossils willoccur.O Fossils are more likely to be preserved in shale depositsthan in deposits of clay and silt.O The shells of organisms can be preserved by processes ofchemical precipitation or mineral exchange.O Freezing enables the soft parts of organisms to survivelonger than the hard parts.O Comparatively few fossils are found in the terrestrialdeposits of streams and lakes.O Thin films of carbon may remain as an indication of softtissue or actual tissue may be preserved if exposure to bacteria islimited.查看正确答案和解析版权声明：本原创文章版权归“智课外语网（参考答案：1.32.13.14.45.36.47.28.39.210.311.412.213.114.Environmental characteristics.The shells of organisms.Thin films of carbon.如果想想生物在死之后被完全摧毁的种种方式，能够这样频繁出现化石是一件很令人惊讶的事。食腐动物和细菌的破坏、化学性腐烂、腐蚀以及其它地质因素都会非常不利于保存。不过，如果生物体碰巧具有矿化的骨骼并且死于可以迅速被沉积物掩埋的地方，摆脱被完全摧毁的几率便会大大增加。海底通常就具有上述的两方面条件，这里生活着很多带壳的无脊椎动物（没有脊椎的动物），不断累积的似雨的沉积颗粒会把它们掩埋起来。虽然多数的化石是在海洋沉积岩中发现的，但是在溪流和湖泊留下的陆相沉积物中也发现过。有时，浸入焦油和流沙、陷入冰或熔岩流或被急速降落的火山灰吞噬的动植物得以保存下来。术语“化石”常常意味着石化，字面意思就是变成了石头。生物体死后，软组织一般会被食腐动物和细菌吃掉。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。事实上，我们现在所知的在沉积物中发现的海洋无脊椎动物保存良好的壳已超过了 1 亿年之久。不过，很多海洋生物的骨骼是由称为霰石的各式碳酸钙矿物质组成的。虽然霰石与我们更为熟悉的矿物方解石具有同样的组成，但是它的晶型不同，相对不稳定，最终会变成更稳定的方解石。很多其他过程也许会改变哈喇壳或蜗牛壳并且增加它被保存下来的几率。含有溶解的二氧化硅、碳酸钙或铁的水可能会在封闭的沉积物中流动，并沉积到诸如骨髓腔和骨头管道内，这些骨头管道曾经由血管和神经占据。这种情况下，骨和壳的原始组成没有改变，但是形成的化石更坚硬并且更持久。这种在孔隙中填充化学沉积物的过程就叫做“完全矿化”。石化还可能同时涉及死亡的动植物的原有物质与不同组成的矿物质的交换作用。该过程叫做“置换作用”，因为溶液溶解了原始物质并将其置换成为等体积的新物质。置换是一个让人难以置信的精确过程，贝壳装饰的细节、树木的年轮以及骨骼的精细结构都被精准地保存下来。另一种类型的石化，称为“碳化”，当软组织以碳薄膜的形式保存时会发生碳化。树叶和软体动物例如水母或蠕虫的组织可能会堆积起来，被掩埋并被压实，然后其中的挥发性成分会消失。碳通常以一种黑色轮廓的形式被保留下来。虽然拥有坚硬的部分的确会增加保存的可能性，但是具有软组织和器官的生物偶尔也会被保存下来。在针叶树以及某些其它的树种的凝固树脂中就发现了昆虫甚至是很小的无脊椎动物。对岩石薄片的 X 射线检查有时会发现可怕的触角轮廓、消化道和很多种海洋生物的视觉器官。冻土或石油渗漏时渗出的焦油中保存了包括皮肤、毛发和冰河时代猛犸象的内脏在内的软组织。