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PASSAGE 3
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
5) 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-
10) ocean ridges and sinking currents under the con-tinents. Theoretically, this convection would carry the continental plates along as though they were on a conveyor belt and would provide the forces needed to produce the split that occurs
15) 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
20) 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 certainly does not occur along
25) lines broken by frequent offsets or changes in direction, as the ridge is. Also it is difficult to seehow 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
30) 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 sink-ing part of the plate, which is denser than the
35) 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 asinking part.
40)
* Another possibility is that the sinking plate cools the neighboring mantle and produces con-vection 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
45) Japan. These seas have a typical oceanic floor,except that the floor is overlaid by several kilo-meters of sediment. Their floors have probably been sinking for long periods. It seems possible that a sinking current of cooled mantle material
50) 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 in because, addi-tion to the enclosed seas that are developing at present behind island arcs, there are a number of
55) older ones of possibly similar origin, such as theGulf of Mexico, the Black Sea, and perhaps the North Sea.
整篇文章看着比较晕，看了好几遍才把题目基本做完。关键可能就是里面的一些关键单词不认识导致了极大的阅读障碍。下面这道题还没完全搞明白。
6. Which of the following, if it could be demonstrated,would most support the traditional view of oceanformation?
(A) Convection usually occurs along lines.
(B) The upper mantle behaves as a dense solid.
(C) Sedimentation occurs at a constant rate.
(D) Sinking plates cool the mantle.
(E) Island arcs surround enclosed seas.
答案A。原文中有这句话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. 似乎可以对应起来，但关键应该是后半句中吧，选项A中并没有这个意思。如果是排除法的是怎么排除其他选项的？
如果有哪位同学手头有中文翻译的能否贴出来给我参考一下，谢谢了！文章中有几句话看不太明白，已经用红色加下划线标出。
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.
这里的back-coupling作何解释？
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.
跟不上这句话的逻辑：为什么no intermediate trench就能推导出 the two ridges远离彼此？为什么会认为后面那个the rising convection currents kept exact pace with them是odd的？
Another possibility is that the sinking plate cools the neighboring mantle and produces con-vection currents that move the plates.
为什么cools the neighboring mantle会导致后面的produces convection currents? 我理解的这两个动作是因果关系，不知道是否有问题？ |
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发表于 2010-3-13 15:01:41
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