Argument47 第一次发帖，大家多多关照~！

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TOPIC: ARGUMENT47 - Scientists 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.
WORDS: 484          TIME: 00:34:11          DATE: 2010/7/24 12:05:11
In this argument, the author asserts that the reason for earth cooling phenomenon in the mid-sixth century was volcanic eruption. To support his view, the author points out  Asia and Europe both suffered from a dimming of the sunlight and freezely cold weather. He also cites records that mentioned a loud boom that might caused by a volcanic eruption, which was contribute to blocking the sunlight and lowering the temperatures. Close scrutiny of these evidence, however, reveals that it lends little credible support to author's claim.
A theshold problem with the argument involves that the author eliminates the possibility of a large meteorite collision for there was no historical records of the bright flash of light, which always occurs with the collision. However, the fact the no existing evidence does not necessarily indicate that there was no such thing in history. It is entirely possible that it was the  large meteorite collision that caused the cold weather, but no one at that time recorded the whole event. The author's failure to substantiate that never in history at that time did a collision happen renders the conclusion based upon it highly suspect.
Even assuming that it is not because a meteorite collided with the earth that the temperature began to lower, the author unfairly equates a loud boom with a volcanic eruption. The volcanic eruption would burst out a loud boom doesn't mean that a loud boom is sure to be caused by erutpion. Perhaps an earthquake  in the mid-sixth century was the reason for the boom;or perhaps a hurricane attacked the earth, which blew down hundreds of trees. Without better evidence that the loud boom was caused by a volcanic eruption or there really was a volcanic erupted in Asia at that time, the argument remains unconvincing.
Even assuming that a volcanic eruption happened in the mid-sixth century, the argument suffers from "either-or" reasoning. Admittedly, dimming of sunlight and low temperature is somewhat related to volcanic eruption. A correlation in one indication of a causal relationship, but in itself does not suffice to prove such a relaitonship. The author overlooks the possibility that other natural disasters, such as storm, tsunami, the number of sunspots caused the change of the weather. Without considering and ruling out other alternative explanations for the issue, the author cannot convince me that a volcanic eruption contributes to the change of weather pattern in the mid-sixth century.
In sum, the argument is unconvincing as it stands. To bolster the argument, the author must provide clear evidence that there was no meteorite colliding with the earth during that period. The author must also substantiate that the loud boom recorded in Asican history was caused by a volcanic eruption. To better assess the argument, I need more information about great natural events and disasters happened in the mid-sixth century which may also cause the change of weather pattern.