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1、GMAT 考试阅读资料 (五 )(4)Passage 26In choosing a method for determining climatic condi-tions that existed in the past， paleoclimatologistsinvokefour principal criteria. First， the material-rocks ， lakes ，vegetation ， etc-on which the method relies must be 5widespread enough to provide plenty of informatio
2、n，sinceanalysis of material that is rarely encountered willnot permit correlation with other regions or with otherperiods of geological history. Second ， in the process offormation ， the material must have received an environ-10 mental signalthat reflects a change in climate and thatcan be deciphere
3、d by modern physical or chemicalmeans. Third， at least some of thematerial must haveretained the signal unaffected by subsequent changes inthe environment. Fourth， it must bepossible to deter- 15 mine the time at which the inferred climatic conditionsheld. This last criterion is more easily met in d
4、atingmarine sediments ， because dating of only a smallnumber of layers in a marine sequence allows the ageofother layers to be estimated fairly reliably by extrapola-(20)tion and in terpolatio n. By con trast, because sedime nta-tio n ismuch less continu ous in con ti nen tal regi ons, esti-mat ing
5、theage of a continen tal bed from the known ages of beds above and below is more risky.One very old method used in the inv estigati on of past(25) climatic con diti ons invo Ives the measureme nt of waterlevels in an cie nt lakes. In temperate regi ons, therearee no ugh lakes for correlati ons betwe
6、e n them to give us areliable picture .In arid and semiarid regi ons , on theother hand , the small number of lakes and the great (30) distances betwee n them reduce the possibilities for corre-lati on.Moreover , since lake levels are con trolled by ratesof evaporati on as well as by precipitati on,
7、 the in terpreta-tio n ofsuch levels is ambiguous. For in sta nee, the factthat lake levelsin the semiarid southwester n Un ited(35) States appear tohave bee n higher duri ng the last ice agetha n they are now was at one time attributed toin creased precipitatio n. On the basis of snow-line eleva-ti
8、ons, however , it has been concluded thatthe climatethe n was not n ecessarily wetter tha n it is now, butrather (40) that both summers and winters were cooler,result ing inreduced evaporati on.Ano ther problematic method is to recon struct formerclimates on the basis of polle n profiles. The type o
9、f vege-tati on in a specific regi on is determ ined by ide ntify ing(45) and coun ti ng the various polle n grains found there.Although the relati on ship betwee n vegetati on an dclimate is not as direct as the relati on ship betwee nclimate and lake levels , the method ofte n works well in the tem
10、perate zon es. In arid and semiarid regi ons in (50) which there is not much vegetation , however , smallchanges in one or a few pla nt types can cha nge thepicture dramatically, makingaccurate correlati onsbetwee n n eighbori ng areas difficult toobta in.1. Which of the followi ng stateme nts about
11、 thediffere nee betwee n mar ine and con ti nen talsedime ntatio n issupported by information in thepassage ?(A) Data provided by dati ng mar ine sedime ntati onis more con siste nt with researchers' findings in other discipli nes tha n is data provided by dati ng con ti nen tal sedime ntatio n.
12、(B) It is easier to estimate the age of a layer in a seque nee of continen tal sedime ntati on tha n it is to estimatethe age of a layer in a seque nee of marine sedime ntati on.(C) Mar ine sedime ntatio n is much less widespread than con ti nen tal sedime ntatio n.(D) Researchers are more ofte n fo
13、rced to rely on extrapolati on whe n dati ng a layer of mar ine sedime ntatio ntha n whe n dat ing a layer of con ti nen tal sedime ntatio n.(E) Marine sedimentation is much more continuous than is continen tal sedime ntati on.2. Which of the followi ng stateme nts best describesthe orga ni zati on
14、of the passage as a whole ?(A) The author describes a method for determining past climatic con diti ons and the n offers specific examples of situati ons in which it has bee n used.(B) The author discusses the method of dat ing marine and con ti nen tal seque nces and the n expla ins how dati ng is
15、more difficult with lake levels tha n with polle n profiles.(C) The author describes the com mon requireme nts of methods for determ ining past climaticcon diti onsand the n discusses examples of such methods.(D) The author describes various ways of choos ing a material for determ ining past climati
16、c con diti ons and the n discusses how two such methods have yielded con tradictory data.(E) The author describes how methods for determ ining past climatic con diti ons were first developed and then describes two of the earliest known methods.3. It can be in ferred from the passage thatpaleoclimato
17、logists have con cluded which of thefollowi ngon the basis of their study of sno w-li neelevati ons in thesouthwester n Un ited States?(A) There is usually more precipitation during an ice age because of in creased amounts of evaporatio n.(B) There was less precipitati on duri ng the last iceage tha
18、 n there is today.(C) Lake levels in the semiarid southwestern United States were lower duri ng the last ice age tha n they are today.(D) During the last ice age , cooler weather led to lower lake levels tha n paleoclimatologists had previously assumed.(E) The high lake levels duri ng the last ice a
19、ge may have bee n a result of less evaporatio n rather tha n more precipitatio n.4. Which of the followi ng would be the most likelytopic for a paragraph that logically con ti nues the passage(A) The kinds of pla nts no rmally found in aridregi ons(B) The effect of variati on in lake levels on polle
20、 ndistributi on(C) The material best suited to preserving signals of climatic cha nges(D) Other criteria inv oked by paleoclimatologistswhe n choos ing a method to determ ine past climatic con diti ons(E) A third method for inv estigat ing past climatic con diti ons5. The author discusses lake level
21、s in the southwester nUn ited States in order to(A) illustrate the mecha nics of the relatio nshipbetwee n lake level ,evaporati on , and precipitati on(B) provide an example of the uncertainty invoIved in in terpreti ng lake levels(C) prove that there are not eno ugh an cie nt lakes with which to m
22、ake accurate correlati ons(D) expla in the effects of in creased rates of evaporati on on levels of precipitati on(E) suggest that snow-line elevations are invariablymore accurate tha n lake levels in determ ining rates ofprecipitatio n at various poi nts in the past6. It can be in ferred from the p
23、assage that anen vir onmen tal sig nal found in geological materialwould notbe useful to paleoclimatologists if it(A) had to be in terpreted by moder n chemicalmea ns(B) reflected a cha nge in climate rather tha n aIon g-term climatic con diti on(C) was incorporated into a material as the materialwa
24、s formi ng(D) also reflected subseque nt en vir onmen talchanges(E) was contained in a con ti nen tal rather tha n a marine seque nee7. Accord ing to the passage , the material used todeterm inepast climatic con diti ons must be widespread forwhich of the followi ng reas ons?I .Paleoclimatologists n
25、eed to make comparisons betwee n periods of geological history.n . Paleoclimatologists need to compare materialsthat have supported a wide variety of vegetati on.in . Paleoclimatologists need to make comparisons with data collected in other regi ons.(A)Ionly(B)non ly(C)Iandnonly(D)Iand皿only(E)nand皿o
26、nly8. Which of the followi ng can be in ferred from the passage about the study of past climates in arid and semiarid regions ?(A) It is sometimes more difficult to determ ine pastclimatic con diti ons in arid and semiarid regi ons tha nin temperate regi ons.(B) Although in the past more research ha
27、s bee ndone on temperate regions, paleoclimatologists have recentlyturned their atte nti on to arid and semiarid regi ons.(C) Although more information about past climates can be gathered in arid and semiarid tha n in temperateregions , dating this information is more difficult.(D) It is difficult t
28、o study the climatic history of arid and semiarid regi ons because their climates have ten ded to vary more tha n those of temperate regi ons.(E) The study of past climates in arid and semiarid regions has been neglected because temperate regions support a greater variety of plant and animal life.Wo
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