2. 外语
  3. 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

admin2010-07-14  57
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 layer of the earth behaves as a liquid when it is subjected to small focus for long periods and that differences in temperature under oceans and continents are sufficient to produce movements in the upper layer of the earth with rising currents under the mid- ocean ridges (山脊) and sinking currents under the continents. Theoretically, these movements 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 occur 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 unconvincing because the movements do not normally occur along lines, and it certainly does not occur along lines broken by frequent 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. An alternative theory is that the sinking part of the plate, which is denser than the hotter surroundings, pulls the rest of 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 (地幔) and produces motion currents that move the plates. This last theory is attractive because it gives some hope of explaining the neighboring mantle and produces motion currents that move the plates. This last theory is attractive because it gives some hope of explaining the enclosed seas. These seas have a typical oceanic floor, except that the floor is overlaid by several kilometers of sediment (沉积物). Their floors have probably been sinking for long periods. It seems possible that a sinking current of cooled material on the upper side of the might be the cause of such deep basins. The enclosed seas are an important feature of the earth’s surface and seriously require explanation.
According to the traditional view of the origin of the ocean basins, which of the following is sufficient to move the continental plates?
选项 A、Spreading of ocean trenches.
B、Movements of min-ocean ridges.
C、Sinking of ocean basins.
D、Differences in temperature under oceans and continents.
答案D
解析 见短文第一段的最后两句话，“This view may be correct．Is has the advantage that the currents are driven by temperature differences that themselves depend on the position of the continents．"作者告诉我们真正的动力是大洋与陆地的温度差。
转载请注明原文地址:https://kaotiyun.com/show/9ZKK777K
0

大学英语六级

相关试题推荐
随机试题
最新回复(0)