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
No very satisfactory account of the mechanism that caused the formation of the ocean basins has yet been given. The traditional
No very satisfactory account of the mechanism that caused the formation of the ocean basins has yet been given. The traditional
admin
2019-02-01
30
问题
No very satisfactory account of the mechanism that caused the formation of the ocean basins has yet been given. The traditional view supposes that the upper mantle of the earth behaves as a liquid when it is subjected to small forces for long periods and that differences in temperature under oceans and continents are sufficient to produce con- vection in the mantle of the earth with rising convection currents under the mid-ocean ridges and sinking currents under the continents. Theoretically, this convection would carry the conti- nental plates along as though they were on a conveyor belt and would provide the forces needed to produce the split that occurs along the ridge. This view may be correct: it has the advantage that the currents are driven by temperature differences that themselves depend on the position of the continents. Such a back-coupling, in which the position of the moving plate has an impact on the forces that move it, could produce complicated and varying motions.
On the other hand, the theory is implausible because convection does not normally occur along lines, and it cer- tainly does not occur along lines broken by frequent offsets or changes in direction, as the ridge is. Also it is difficult to see how the theory applies to the plate between the Mid-Atlantic Ridge and the ridge in the Indian Ocean. This plate is growing on both sides, and since there is no intermediate trench, the two ridges must be moving apart. It would be odd if the rising convection currents kept exact pace with them. An alternative theory is that the sinking part of the plate, which is denser than the hotter surrounding mantle, pulls the rest of the plate after it. Again it is difficult to see how this applies to the ridge in the South Atlantic, where neither the African nor the American plate has a sinking part.
Another possibility is that the sink- ing plate cools the neighboring mantle and produces convection currents that move the plates. This last theory is attractive because it gives some hope of explaining the enclosed seas, such as the Sea of Japan. These seas have a typical oceanic floor, except that the floor is overlaid by several kilometers of sediment. Their floors have probably been sinking for long periods. It seems possi- ble that a sinking current of cooled mantle material on the upper side of the plate might be the cause of such deep basins. The enclosed seas are an important feature of the earth’s surface, and seriously require explanation because, in addition to the enclosed seas that are developing at present behind island arcs, there are a number of older ones of possibly similar origin, such as the Gulf of Mexico, the Black Sea, and perhaps the North Sea.
It can be inferred from the passage that, of the following, the deepest sediments would be found in the
选项
A、Indian Ocean.
B、Black Sea.
C、Mid- Atlantic.
D、South Atlantic.
E、Pacific.
答案
B
解析
下列哪个海沉积物最深?关于沉积物问题,文章在第三段举内海之例时提到。∴B正确。A、C、D、E都不是内海的例子。
转载请注明原文地址:https://kaotiyun.com/show/31kO777K
本试题收录于:
GMAT VERBAL题库GMAT分类
0
GMAT VERBAL
GMAT
相关试题推荐
Whatdowemeanbyasatisfactorystandardofliving?Obviously,itmustincludethebasicnecessitiesoflifesuchasfood,clo
Traditionally,universitieshavecarriedouttwomainactivities:researchandteaching.Manyexpertswouldarguethatboththes
Traditionally,universitieshavecarriedouttwomainactivities:researchandteaching.Manyexpertswouldarguethatboththes
Wilson:Hello.MayIspeaktoPeter?Peter:________
Whatdowemeanbyasatisfactorystandardofliving?Obviously,itmustincludethebasicnecessitiesoflifesuchasfood,clo
Woman:DoyougetthePublicBroadcastingSystemonTV?Man:Yes,everybodygetsPBS.【D5】______Woman:It’sboringandoftenput
Scientistssaidtheyhavefoundevidenceofagiantplanetfaroutinoursolarsystem.Inastatement,theCaliforniaInstitute
Economicdevelopmentdependsontheextractionofnaturalresourcesandonlow-skilledlabor,whichhasresultedinaweakmanuf
Entireculturesoperateonelaboratesystemsofindirectness.Forexample,itisdiscoveredinasmallresearchprojectthatmos
Entireculturesoperateonelaboratesystemsofindirectness.Forexample,itisdiscoveredinasmallresearchprojectthatmos
随机试题
肌萎缩性侧索硬化原发性侧索硬化
引起菌群失调的原因是
A、风邪B、寒邪C、暑邪D、湿邪E、火邪具有数变特性的邪气是
针对单纯性乙醇中毒严重患者,下列救治措施,错误的是
_____学生的年龄在12~15岁之间,处于少年期,是人生理发育的第_____个高峰期。
“东周时期,王朝软弱无力,封建主相互混战不绝,表面上是个多事的时期。不过.这也是一个社会经济发生根本变革,从而决定而且永久地决定中国发展进程的时期。”下列说法正确的是:
北京时间2011年3月11日下午1点46分,日本近海发生9级地震,地震引发海啸,并引发核电站爆炸造成大量人员伤亡。加上之前的智利、海地及中国汶川大地震,地震的频繁发生让民众产生恐慌情绪。有人谣传食用碘盐可预防核辐射,海水被放射性物质污染而没法苒提炼盐,广东
白居易在《大林寺桃花》诗中描述道:“人间四月芳菲尽,山寺桃花始盛开。”这两句诗所蕴含的哲学寓意是()。
______.healwaystrieshisbesttocompleteitontime.
Itwassuggestedthattheconstruction______aheadoftime.
最新回复
(
0
)