首页
登录
职称英语
No very satisfactory account of the mechanism that caused the formation of th
No very satisfactory account of the mechanism that caused the formation of th
游客
2025-01-13
24
管理
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 convection in the mantle of the earth with rising convection currents under the mid-ocean ridges and sinking currents under the continent. Theoretically, this convection would carry the continental plates along as though they were on a conveyer 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. On the other hand, the theory is implausible because convection does not normally occur along lines, and it certainly does not occur along lines broken by frequent offsets or changes in direction, as the ridge is.
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.
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 sinking 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 span. 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.
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 possible 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. [br] The author refers to a "conveyer belt"(Para. 1)in order to______.
选项
A、illustrate the effects of convection in the mantle
B、show how temperature differences depend on the positions of the continents
C、demonstrate the linear nature of the Mid-Atlantic Ridge
D、describe the complicated motions made possible by back-coupling
答案
A
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3910575.html
相关试题推荐
[originaltext]Insuranceratesareafactorthatmustbetakenintoaccount.The
[originaltext]Insuranceratesareafactorthatmustbetakenintoaccount.The
[originaltext]Insuranceratesareafactorthatmustbetakenintoaccount.The
OneofLondonZoo’srecentadvertisementscausedmesomeirritation,sopaten
OneofLondonZoo’srecentadvertisementscausedmesomeirritation,sopaten
OneofLondonZoo’srecentadvertisementscausedmesomeirritation,sopaten
[originaltext]James:Hello.I’dliketoopenabankaccount.Clerk:Whattypeo
[originaltext]James:Hello.I’dliketoopenabankaccount.Clerk:Whattypeo
OurculturehascausedmostAmericanstoassumenotonlythatourlanguageis
OurculturehascausedmostAmericanstoassumenotonlythatourlanguageis
随机试题
TheGreekshaveasecondBattleofMarathonontheirhands.Theiradversaries
[originaltext]Ifyou’reconfusedabouthowmuchwateryoureallyneed,I’m
Forthispart,youareallowed30minutestowriteacompositiononthetopicHo
贯彻学校德育疏导原则的基本要求是()。A.讲明道理,疏导思想 B.建立健全规章
患者男,34岁,左足麻木、疼痛、走路时小腿酸胀,易疲劳,足底有硬胀感,初步诊断为
流行性腮腺炎主要侵犯的经脉是A.足厥阴肝经 B.足少阳胆经 C.足太阳膀胱经
不会引起白细胞数量增多的疾病是()。A.流行性出血热 B.伤寒 C.狂
员工因接受实施股票期权计划企业授予的股票期权获得的所得,应按照个人所得税的()税
近年来,春晚愈发注重________传统文化魅力,表达时代关切和人文情怀。在这每
隐蔽工程在隐蔽前应通知()及有关方面进行验收,并形成验收文件。A.施工单位质量部
最新回复
(
0
)