小安63篇中的第二十六篇
Passage 26 (26/63)问题解决型（专业性科学文章）
提出四个标准——提出问题In choosing a method for determining climatic conditions that existed in the past, paleoclimatologists invoke four principal criteria*2C. First, the material—rocks, lakes, vegetation, etc.—on which the method relies must be widespread*7 enough to provide plenty of information, since（小原因，可以暂时不看） analysis of material that is rarely encountered will not permit correlation with other regions or with other periods*7 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破译，解码 by modern physical or chemical means. Third, at least some of the material must have retained the signal *6unaffected by subsequent changes in the environment*6D. Fourth, it must be possible to determine the time at which the inferred climatic conditions held. This last criterion is more easily（比较句，很可能出题） met in dating marine sediments*1, because（小原因，暂时不用看） 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（强对比，一定要看）, because（小原因，暂时不用看，看后半句） sedimentation is much less continuous*1E in continental regions*1, estimating the age of a continental bed from the known ages of beds above and below is more risky.
解决方案一：古代湖泊水位法One very old（大-） method*2C used in the investigation of past climatic conditions involves the measurement of water levels in ancient lakes. 原因一In temperate regions温带地区, there are enough lakes for correlations between them to give us a reliable（小+，由于前面有大，所以后面一定有转折） picture. In arid and semiarid regions, on the other hand（转折）, the small number of lakes and the great distances between them reduce the possibilities for correlation. 原因二Moreover（大列举的非第一点）, since lake levels are controlled by rates of evaporation as well as（强调前者） by precipitation降水, the interpretation of such levels is ambiguous*5B（-）. For instance（与结论紧密相连，篇幅小，可以暂时不看）, the fact that lake levels in the semiarid southwestern United States*5 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 snow-line elevations*3, however（其实还是紧跟上一个例子，可以暂时不看）, it has been concluded*3 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*3E.
解决方案二：花粉法Another problematic（大-） 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（by doing通常都是很重要的内容） the various pollen grains found there. Although（转折的前半句可以不读） the relationship between vegetation and climate is not as direct as the relationship between climate and lake levels, the method often works well（小+） 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*8A（-） to obtain.
8. Which of the following can be inferred from the passage about the study of past climates in arid and semiarid regions?INFER
(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.作者: bodkicker 时间: 2012-4-18 06:43
