首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal cri
In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal cri
admin
2014-09-18
65
问题
In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal criteria. First, the material— rocks, lakes, vegetation, etc—on which the method relies must be widespread enough to provide plenty of information, since analysis of material that is rarely encountered will not permit correlation with other regions or with other periods of geological history. Second, in the process of formation, the material must have received an environmental signal that reflects a change in climate and that can be deciphered by modern physical or chemical means. Third, at least some of the material must have retained the signal unaffected by subsequent changes in the environment. Fourth, it must be possible to determine the time at which the inferred climatic conditions held. This last criterion is more easily met in dating marine sediments, because dating of only a small number of layers in a marine sequence allows the age of other layers to be estimated fairly reliably by extrapolation and interpolation. By contrast, because sedimentation is much less continuous in continental regions, estimating the age of a continental bed from the known ages of beds above and below is more risky.
One very old method used in the investigation of past climatic conditions involves the measurement of water levels in ancient lakes. In temperate regions, there are enough lakes for correlations between them to give us a reliable picture. In arid and semiarid regions, on the other hand, the small number of lakes and the great distances between them reduce the possibilities for correlation. Moreover, since lake levels are controlled by rates of evaporation as well as by precipitation, the interpretation of such levels is ambiguous. For instance, the fact that lake levels in the semiarid southwestern United States appear to have been higher during the last ice age than they are now was at one time attributed to increased precipitation. On the basis of snowline elevations, however, it has been concluded that the climate then was not necessarily wetter than it is now, but rather that both summers and winters were cooler, resulting in reduced evaporation.
Another problematic method is to reconstruct former climates on the basis of pollen profiles. The type of vegetation in a specific region is determined by identifying and counting the various pollen grains found there. Although the relationship between vegetation and cli- mate is not as direct as the relationship between climate and lake levels, the method often works well in the temperate zones. In arid and semiarid regions in which there is not much vegetation, however, small changes in one or a few plant types can change the picture dramatically, making accurate correlations between neighboring areas difficult to obtain.
Which of the following can be inferred from the passage about the study of past climates in arid and semiarid regions?
选项
A、It is sometimes more difficult to determine past climatic conditions in arid and semiarid regions than in temperate regions.
B、Although in the past more research has been done on temperate regions, paleoclimatologists have recently turned their attention to arid and semiarid regions.
C、Although more information about past climates can be gathered in arid and semiarid than in temperate regions, dating this information is more difficult.
D、It is difficult to study the climatic history of arid and semiarid regions because their climates have tended to vary more than those of temperate regions.
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.
答案
A
解析
关于干旱、半干旱区古气候研究,哪一点可从原文推出?A.正确。有时确定干旱、半干旱区古气候比温和湿润区要难。第二段湖水位法、第三段花粉测定法都能推出这个结论。B.过去研究温润区,现在学者更关注干旱区。原文无。C.干旱区过去气候资料能更多得到。无。D.“vary more”原文无。E.“neglected”原文未提。
转载请注明原文地址:https://kaotiyun.com/show/KctO777K
本试题收录于:
GMAT VERBAL题库GMAT分类
0
GMAT VERBAL
GMAT
相关试题推荐
Itseemslikeeverydaythere’ssomenewresearchaboutwhetherourfavoritedrinksaregoodforus.Oneday,sciencesaysagla
Inwhatnowseemsliketheprehistorictimesofcomputerhistory,theearlypost-warera(战后时期),therewasaquitewidespreadc
"Equalpayforequalwork"isaphraseusedbytheAmericanwomenwhofeelthattheyareunfairlytreatedbysociety.Theysayi
Imagineaschoolthatexpecteditsstudentstobecomeliterate(有读写能力的)withoutanyformalinstruction.Mostparentswouldbeal
Thegovernmenthaslostagreatdealof______becauseofthelargeincreaseinfoodprices.
Wehave______tothegovernmentforahomeimprovementloan.
IntheUnitedStates,30percentoftheadultpopulationhasa"weightproblem".Tomanypeople,thecauseisobvious:theyeat
InChinaitisrelativelyusualtoaskpeopletheirage,butintheWestthisquestionisgenerallyregardedasimpolite.Thisi
Crimehasitsowncycles,amagazinereportedsomeyearsago.Policerecordsthatwerestudiedforfiveyearsfromover2400cit
Alltheirattemptsto_________thechildfromtheburningbuildingwereinvain.
随机试题
甲公司欲在路边盖门面房,但路边的树枝阻碍了施工。在未取得采伐许可的情况下,甲公司将部分树枝砍掉,所砍树枝共计6立方米。对于甲公司的行为认定,下列哪些选项是错误的?()
关于生长激素作用的叙述,错误的是
治疗血虚证的代表方剂
分部(子分部)工程质量验收合格的规定包括()。
在我国不具备《中华人民共和国教师法》规定的教师资格学历的公民,无法获取教师资格。()
阅读下面短文,完成46—50题。“道”是什么?《辞源》上的解释主要是道路、方法与规律;《大不列颠简明百科全书》上的解释主要是世界的本原和规律。此百科全书还特别注明:庄子认为,“道”是终极本原,是无所不载、无所不覆、自生自化的宇宙本体。
五四运动是一次关于理想和信念的活动,要你组织一次纪念五四的活动,你怎么组织?
在VFP6.0的报表设计中,为报表添加标题的正确操作是______。
某学校初中二年级五班的物理老师要求学生两人一组制作一份物理课件。小曾与小张自愿组合,他们制作完成的第一章后三节内容见文档“第3—5节.pptx”,前两节内容存放在文本文件“第1—2节.pptx.”中。小张需要按下列要求完成课件的整合制作:在第
DVDrentalkiosks(售货亭)fromRedboxandBlockbusterseemtobepoppinguponeverycornerthesedays,buthome-videomarketanalys
最新回复
(
0
)