Question24-25 When volcanic lava solidifies, it becomes uniformly magnetized in the direction in which the Earth's magnetic field points. There are significant differences in the direction of magnetization among solidified lava flows from different volcanoes that erupted at different times over the past several million years. Therefore, it must be that the direction of the Earth's magnetic field has changed over time. Since lava flows differing by thousands of years in age often have very similar directions of magnetization, the change in the direction of the Earth's magnetic field must take place very gradually over hundreds of thousands of years. 25. Which one of the following, if true, most seriously undermines the conclusion that the change in the direction of the Earth's magnetic field happened very slowly? (A) The changes in the direction of the Earth's magnetic field are determined by the chaotic movement of iron-containing liquids in the Earth's outer core. (B) There has not been a change in the direction of the Earth's magnetic field since scientists have begun measuring the direction of magnetization of lava flows. (C) The direction of the Earth's magnetic field has undergone a complete reversal several times over the past few million years. (D) A lava flow has been found in which the direction of magnetization in the center of the flow differs significantly from that on the surface, even though the flow took only two weeks to solidity completely. (E) Since the rate at which molten lava solidifies depends on the temperature and altitude of the environment, some lava flows from volcanoes in certain areas will take years to solidity completely. 这个题目我看了有点迷糊，觉得哪个都不像，答案是D。请NN解释一下，D是怎么weaken的。
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发表于 2005-6-17 21:30:00
