Argument47 [OB小组]_第5次作业_6th世纪地球变冷因为火山爆发？

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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: 445+64          TIME: 00:37:00          DATE: 2007-7-17 16:34:23

In this argument, the author concludes that the cooling in the mid-sixth century was probably because of a volcanic eruption. To support this argument, the author cites some accounts found in both Asia and Europe mentioning a dimming of sun and extremely cold temperature. The author also points out that no extant records of the time mention a flash which a large meteorite collision should have and that some Asian historical records of that time mention a loud boom that was like sound of a volcanic eruption. However, this argument suffers from several flaws and is therefore unpersuasive as it stands.

First of all, that accounts found both in Asia and Europe mentioning the a dimming of the sun and extremely cold temperatures dose not necessarily indicate that there was a cooling in the mid-sixth century. Perhaps the dimming of the sun and the extremely cold temperatures the accounts mentioned lasted just for quite short time. Or perhaps those mentioned by the accounts only occurred in a limited area. Without ruling out these and other possibilities, the author cannot make a persuasive conclusion based on these accounts.

Secondly, the author makes his conclusion based on a assumption that there is only two causes-volcanic eruption and large meteorite collision, which can cause the cooling. It is quite possible that the orbit of earth changed at that time so that the earth became cooler. Another possibility is that the sun became cooler at that time and the earth also became cooler. Without accounting for these and other possibilities, the author cannot make me convinced.

Thirdly, the fact that no extant historical records mention the flash of a large meteorite collision has little indication that there was no large meteorite collision. Perhaps the records mentioning such a flash had lost hundreds of years ago. Or perhaps someone had seen this flash, yet nobody took it down to the records. Without considering these and other possible situations, the author cannot make a correct conclusion.

Fourthly, some surviving Asian historical records of the time mentioning a loud boom cannot justify that there was a volcanic eruption. Perhaps the boom mentioned by the Asian historical records was actually the sound of a thunder. Or perhaps it was the sound of the landslip of a hill.

Finally, even assuming there was a volcanic eruption, the author unfairly assumes that the cooling was caused by the volcanic eruption. Without evidence to support this assumption, it is entirely possible that the cooling of the earth was caused by the meteorite collision. Or perhaps the atmosphere changed and reduced the sunlight that reaches the earth. These and other reason can also result in the cooling of the earth.

In sum, this argument is not well supported. To bolster this argument, the author must provide clear evidence that there was indeed a volcanic eruption and that the cooling was caused by the volcanic eruption. To better assess this argument, more information about the cooling in the mid-sixth cooling and more details about the historical records are needed.

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