首页
登录
职称英语
In choosing a method for determining climatic conditions that existed in the
In choosing a method for determining climatic conditions that existed in the
游客
2024-01-13
21
管理
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. [br] It can be inferred from the passage that an environmental signal found in geological material would not be useful to paleo-climatologists if it
选项
A、had to be interpreted by modern chemical means.
B、reflected a change in climate rather than a long-term climatic condition.
C、was incorporated into a material as the material was forming.
D、also reflected subsequent environmental changes.
E、was contained in a continental rather than a marine sequence.
答案
D
解析
文中指出,地质材料中的环境信息如果怎样,对古气候学家就没有用了?推论:见原文L16—19,第三个要求,这些材料中信息不受其后环境变化的影响,取非得:∴D.也反映了其后的环境变化。A、B、C、E和原文叙述不一致。
转载请注明原文地址:https://tihaiku.com/zcyy/3359114.html
相关试题推荐
Theydidnotfind______topreparefortheworstconditionstheymightmeet.A、wor
Toimprovethe______isregardedasagoodmethodtoincreasethefarmer’sincome
TheChinesehaveusedamethodcalledacupuncturetohelpperformoperations
TheChinesehaveusedamethodcalledacupuncturetohelpperformoperations
TheChinesehaveusedamethodcalledacupuncturetohelpperformoperations
TheChinesehaveusedamethodcalledacupuncturetohelpperformoperations
TheChinesehaveusedamethodcalledacupuncture(针炙)toperformoperations
TheChinesehaveusedamethodcalledacupuncture(针炙)toperformoperations
TheChinesehaveusedamethodcalledacupuncture(针炙)toperformoperations
Withtheconstantchangeofconditions,theoutcomeisnotalways________.A、favo
随机试题
Scientistsfindthathard-workingpeoplelivelongerthanaveragemenandwo
America’sBrainDrainCrisisLosingtheG
[originaltext]M:Sowhat’sthenextthingontheagenda,Mary?W:Well,it’sth
向斜构造的特征是( )。A.两侧地层新、中间地层老 B.两侧地层老、中间地层
蛋白质—能量营养不良
嗳气频作而响亮,发作因情志变化而增减,其病因是A.肝气犯胃B.宿食内停C.脾胃虚
工程招标时,工程量难以确定的建设项目适用于()合同形式。A:固定总价 B:可
可乐定的降压机制是A.激动外周α1受体 B.影响NA.释放 C.扩张血管
在清洁卫生服务内容中,对于建筑物内公共区域清洁来说,建筑物内公共区域清洁包括(
施工图预算对施工单位的作用有( )。A.施工图预算是拨付进度款及办理结算的依据
最新回复
(
0
)