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
2018-06-06
79
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.
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://kaotiyun.com/show/S2SO777K
本试题收录于:
NAETI中级口译笔试题库外语翻译证书(NAETI)分类
0
NAETI中级口译笔试
外语翻译证书(NAETI)
相关试题推荐
Itshallbewrongifnotconsiderhowmuchmoneyyouhavebeforegoingabroadtostudy.
Theresearchersstresstheurgencyofpreservingoldvarietiesasbothdisease-resistantstrainsandonesthatwillthrivewitho
Howmuchphysicalactivityshouldteenagersdo,andhowcantheygetenough?Manyteenagersspendalot
Howmuchphysicalactivityshouldteenagersdo,andhowcantheygetenough?Manyteenagersspendalot
AccordingtotherecentresearchofNortheasternUniversity,our________sensitivitydecreaseswithage.Byage60,mostpeopleh
我们需要的是一种“宽容的文化”,一种与人们认同开放的外向型精神需求相适应的方法。宽容不是指对那些我们认为是“其他人”的人漠不关心,也不是对他们的文化、宗教、背景与起源漠然置之。宽容需要我们了解并理解这些“其他人”。当熟悉的体制不复存在,国界变得无
A、Theyinheritedbytheirparents.B、Theyhavethisnaturallyencodedintheirgenes.C、Theylearnbylisteningtoothersofthe
A、Theybuythingstosavemoney.B、Theyareeasilyexcitedatplayinggames.C、Smallbudgetsmakeitnecessaryforthemtobuyc
Formostofus,workisthecentral,dominatingfactoflife.Wespendmorethanhalfourconscioushoursatwork,preparingfor
Humanshavealwaysbeenfascinatedbydreams.ThevividdreamspeoplerememberandtalkaboutareREMdream—thetypethatoccur
随机试题
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性。
早期自然流产多是由于
体积较小的无症状单发的肉瘤如何处理()肉瘤体积较大者最宜采用的方法是()
知母的药理作用包括()
建筑消防设施的合格证明文件有()。
银行不予受理的结算凭证有()。
劳动力成为商品的条件是劳动者()。
车子在___________的盐碱戈壁上颠簸,疑惑越来越浓:___________的地方,人怎能存活?但是地图上标得十分清晰:新疆喀什英吉沙县托普鲁克乡木孜鲁克村。世人闻知英吉沙县是小刀与达瓦孜之乡、非遗古镇、新疆水城、中国杏都,等等,却很少有人知道它还有
编写如下程序:PrivateSubCommand1_Click()Fori=1To5PrintTab(6-i);Forj=iTo1Step-1Pri
面向对象方法中,继承是指( )。
最新回复
(
0
)