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发表于 2006-7-10 22:13:44
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47Scientists studying historical weather patterns have discovered that in the mid-sixth century, Earth suddenly became significantly cooler. Although few historical records survive from that time, some accounts found both in Asia and Europe mention a dimming of the sun and extremely cold temperatures. Either a huge volcanic eruption or a large meteorite colliding with Earth could have created a large dust cloud throughout Earth's atmosphere that would have been capable of blocking enough sunlight to lower global temperatures significantly. A large meteorite collision, however, would probably create a sudden bright flash of light, and no extant historical records of the time mention such a flash. Some surviving Asian historical records of the time, however, mention a loud boom that would be consistent with a volcanic eruption. Therefore, the cooling was probably caused by a volcanic eruption.
字数:476
This argument concludes that the significantly cooling in the mid-sixth century was probably caused by a volcanic eruption. To justify this conclusion, the argument points out that either a huge volcanic eruption or a large meteorite colliding with Earth could lower global temperatures. Since no extant historical records mention the sudden bright flash created by the large meteorite collision, and a loud boom consistent with a volcanic eruption was mentioned in Asian historical records, thus it is a volcanic eruption that caused the cooling. However, this argument is unpersuasive in several reasons.
First of all, no historical records mention the sudden bright flash does not mean that there is no meteorite collision in that time. Probably there are indeed historical records that mention the sudden bright flash, but these records were lost due to wars or other unpredictable factors. Or the collision happened in desolate area such as deserts, Arctic and Antarctic or happened in seas. So no people could observe this phenomenon, and no historical records that mention the bright flash came down. Even if few people observed the flash when it happened, yet they could not record it because these people might be illiterate.
Secondly, the loud boom mentioned in Asian historical records of the time might not be created by volcanic eruption. Maybe the loud boom just happened at that time and there is no cause and effect relationship between volcanic eruption and the boom. Hence, it is entirely possible that the boom was caused by other things, such as earthquake. In addition, the argument does not account for whether or not the boom happened before the cooling. If temperatures had already fallen before the occurrence of the boom, then the cooling might be irrelative with the boom, which is thought to be created by volcanic eruption. So it can be concluded that the cooling might also be irrelative with the volcanic eruption.
Finally, the conclusion in the argument seems a little arbitrary, since the author argues that the cooling can only be caused by either a huge volcanic eruption or a large meteorite collision. Even if the cooling was not caused by meteorite collision, it is too hasty to conclude that volcanic eruption caused it. Probably, there are other factors that could also lower the global temperatures, such as the variation of magnetic field or the burst of macula. In these events, the conclusion is unreliable.
In sum, this argument is specious. To bolster it the author must provide clear evidence that the meteorite collision did not happen indeed. I would also need to know that whether or not the loud boom was caused by volcanic eruption and there was cause and effect relationship between the boom and the cooling. In addition, the author should prove that besides the eruption and collision, there were no other factors that could cause the cooling.
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