argument47 加州阳光第五次作业

riverwUID: 2199459

47. 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.

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1. 未考虑其它原因（fallacy of false dilemma)
2. 没有flash记录并不能说明未发生过，发生过人们未必看到
3. 有记录的声响未必是火山喷发，而且火山喷发未必足够影响地球气候（大小）

In this argument the arguer concludes that the significant decrease of global temperatures in the mid-sixth century was caused by a volcanic eruption. To support the conclusion, the arguer provides evidences as follows: (1) Either a huge volcanic eruption or a large meteorite colliding with Earth can lead to the decrease of global temperatures; (2) No extant historical records mention a bright flash which might be created by a large meteorite collision; and (3) Some surviving Asian historical records of the time mention a loud boom that would be consistent with a volcanic eruption. This argument is well presented but not convincing as it stands since it actually suffers from several critical flaws.

In the first place, the arguer unfairly constrains the possible explanation to either a huge volcanic eruption or a large meteorite collision, whereas there might be alternative reasons which could also lead to the temperature decrease. The alternative explanations can be sun's abnormal activities, or certain periodic movements of solar systems in the Milk Way, or even some other factors which are not disclosed by human yet. Moreover, it is also possible that both volcanic eruption and meteorite collision worked together to lower the global temperatures since these two natural events are absolutely not mutually exclusive. Before these potential alternative explanations are carefully considered and ruled out, it is too early to conclude which one finally caused the ancient temperature changes.

Another problem of the argument involves a presumptuous assumption that no large meteorite collision happened at that time, which is not necessarily the truth. The arguer admits that a large meteorite collision merely probably creates a sudden flash of light, so it is possible that some large meteorite collisions might happen without any flash at that time. Furthermore, the possible meteorite collision might happen at those places where no human being lives, such as deserts or primitive forests, hence nobody could see the flash if there was. In this case, the arguer's assumption lends no support to but undermine the argument.

Finally, the reasoning that a loud boom recorded in some surviving Asian historical records of the time relates to a huge volcanic eruption is open to doubt. The arguer fails to provide any evidence to justify the loud boom is caused by a volcanic eruption. Some other natural events could also create such loud boom such as hill body collapse and earthquake. Moreover, even if a volcanic eruption did happen and caused the loud boom, it might be too small to create a large dust and eventually lower the global temperatures significantly. Thus the theory that volcanic eruption caused the earth becoming cooler is quite suspicious.

In conclusion, this argument is unconvincing as it stands. To strengthen it the arguer should have to analyze and rule out other alternative explanations of the sudden significant decrease of global temperatures. The arguer must also provide evidence that meteorite collision did not happen at the time, and more clear information about the connection of the loud boom and volcanic eruption.