首页
登录
职称英语
No very satisfactory account of the mechanism that caused the formation of t
No very satisfactory account of the mechanism that caused the formation of t
游客
2024-01-13
32
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 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. [br] 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://tihaiku.com/zcyy/3357473.html
相关试题推荐
______shouldanymoneybegiventoasmallchild.A、OnnoaccountB、Fromallacc
Onnoaccount______heldresponsiblefortheaccident.A、thedrivercanbeB、cant
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
WehavequiteabitofinformationaboutancientEgyptianmedicine.Doctors’i
随机试题
Whichofthefollowingitemsarereportedasacurrentliabilityonthebalance
Thedirectraysofthesuntouchtheequatorandstrikenorthwardtowardthe
下列各项中,关于河南红色旅游景点的说法正确的有( )。A.新县被誉为“红军的故
根据有关规定,一般来说,基金份额持有人的权利不包括()。A.参与分配清算后的剩
( )就是要在指导投资者分析投资问题、获得必要信息、进行理性选择的同时,致力于改
血块收缩能力增高见于A、原发性血小板减少性紫癜B、血小板增多症C、血小板无力
对成人实施心肺复苏抢救时,按压通气之比为()。A.单人施救为30:2,双人为1
法律关系的构成要素是指( )A、主体和客体 B、权利和义务 C、主体、客体和
某男性患者,30岁。因龋坏拔除,给予2%利多卡因行下牙槽神经阻滞麻醉,未行注射器
甲电池制造厂主要生产销售电池,其将自产的电池用于下列各项用途,应当缴纳消费税的有
最新回复
(
0
)