托福TPO阅读真题全套【译文 解析】

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托福TPO阅读真题全套【译文+解析】
摘要：托福tpo阅读真题全套【译文+解析】下载，不少参加托福考试的牛人考前都会将托福tpo阅读真题全套内容看个2-3遍，真正吃透以里面的内容，你看了吗？
托福tpo阅读真题全套【译文+解析】全部是之前考试过得真题，它里面的题目的出题点和难度与真题非常接近，是我们参加托福考试的考生必不可少的精华材料，下面我们就来看一下有关托福tpo阅读真题的部分内容。
托福tpo阅读真题全套:TPO24

FossilPreservation
Whenoneconsidersthemanywaysbywhichorganismsarecompletelydestroyedafterdeath,itisremarkablethatfossilsareascommonastheyare.Attackbyscavengersandbacteria,chemicaldecay,anddestructionbyerosionandothergeologicagenciesmaketheoddsagainstpreservationveryhigh.However,thechancesofescapingcompletedestructionarevastlyimprovediftheorganismhappenstohaveamineralizedskeletonanddiesinaplacewhereitcanbequicklyburiedbysediment.Bothoftheseconditionsareoftenfoundontheoceanfloors,whereshelled
invertebrates(organismswithoutspinesflourishandarecoveredbythecontinuousrainofsedimentaryparticles.Althoughmostfossilsarefoundinmarinesedimentaryrocks,theyalsoarefoundinterrestrialdepositsleftbystreamsandlakes.Onoccasion,animalsandplantshavebeenpreservedafterbecomingimmersedintarorquicksand,trappediniceorlavaflows,orengulfedbyrapidfallsofvolcanicash.
Theterm"fossil"oftenimpliespetrifaction,literallyatransformationintostone.Afterthedeathofanorganism,thesofttissueisordinarilyconsumedbyscavengersandbacteria.Theemptyshellofasnailorclammaybeleftbehind,andifitissufficientlydurableandresistanttodissolution,itmayremainbasicallyunchangedforalongperiodoftime.Indeed,unalteredshellsofmarineinvertebratesareknownfromdepositsover100millionyearsold.Inmanymarinecreatures,however,theskeletoniscomposedofamineralvarietyofcalciumcarbonatecalledaragonite.Althougharagonitehasthesamecompositionasthemorefamiliarmineralknownascalcite,ithasadifferentcrystalform,isrelativelyunstable,andintimechangestothemorestablecalcite.
Manyotherprocessesmayaltertheshellofaclamorsnailandenhanceitschancesforpreservation.Water
containingdissolvedsilica,calciumcarbonate,orironmaycirculatethroughtheenclosingsedimentandbedepositedincavitiessuchasmarrowcavitiesandcanalsinboneonceoccupiedbybloodvesselsandnerves.Insuchcases,theoriginalcompositionoftheboneorshellremains,butthefossilismadeharderandmoredurable.Thisadditionofachemicallyprecipitatedsubstanceintoporespacesistermed"permineralization."
Petrifactionmayalsoinvolveasimultaneousexchangeoftheoriginalsubstanceofadeadplantoranimalwith
mineralmatterofadifferentcomposition.Thisprocessistermed"replacement"becausesolutionshavedissolvedtheoriginalmaterialandreplaceditwithanequalvolumeofthenewsubstance.Replacementcanbeamarvelouslypreciseprocess,sothatdetailsofshellornamentation,treeringsinwood,anddelicatestructuresinboneareaccuratelypreserved.
Anothertypeoffossilization,knownascarbonization,occurswhensofttissuesarepreservedasthinfilmsofcarbon.



Leavesandtissueofsoft-bodiedorganismssuchasjellyfishorwormsmayaccumulate,becomeburiedandcompressed,andlosetheirvolatileconstituents.Thecarbonoftenremainsbehindasablackenedsilhouette......
以上就是有关托福tpo阅读真题的部分内容，今天我们就先介绍到这里，稍后我么陆续为大家介绍更多有关托福口语、听力、写作的TPO全套内容，敬请期待。
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托福TPO阅读真题全套【译文 解析】

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