argument50 -anan

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Argument50  第16篇 让砖头来得更猛烈些吧！
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作者：寄托家园作文版普通用户     共用时间：20分1秒     199 words
从2007年3月12日11时24分到2007年3月12日11时20分
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From a draft textbook manuscript submitted to a publisher.
'As Earth was being formed out of the collision of space rocks, the heat from those collisions and from the increasing gravitational energy of the planet made the entire planet molten, even the surface. Any water present would have evaporated and gone off into space. As the planet approached its current size, however, its gravitation became strong enough to hold gases and water vapor around it as an atmosphere. Because comets are largely ice made up of frozen water and gases, a comet striking Earth then would have vaporized. The resulting water vapor would have been retained in the atmosphere, eventually falling as rain on the cooled and solidified surface of Earth. Therefore, the water in Earth's oceans must have originated from comets.'
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The argument is well-stated, but not thoroughly well-reasoned. The arguer’s assertion that only because comets are largely ice made up frozen water and gases,  the water in Earth’s oceans must have originated from comets is great premature. I would not agree with such assertion, as discussed below.

The threshold problem in the argument is the speaker's assumption that a comet ever stroked Earth. In this manuscript, there is no evidence that such things had happened. If none comet stroked Earth, then how can the speaker show us that the water in Earth's oceans must have originated from comets?

Even it is true that a comet had ever stroked Earth, still another question worth considering is that when it stroked. The speaker also cannot provide any evidence to support that such striking happened after Earth's gravitation became strong enough to hold gases and water vapor around it as an atmosphere. Lacking such convincing evidence, it is extremely possible that the striking occurred before that time that the gravitation was strong enough to hold gases. For that matter, as the speaker's states--any water present would have evaporated and gone off into space, if so, even a comet stroked Earth, also any water in Earth would not originated from it.

Even though, it is necessary to point out that attention should be paid to the size of comet and the water content of it. Perhaps the comet striking Earth is just a small one, or perhaps the ice made up frozen water in it is the same little. For that matter, the water brought by comet is far enough to the need of a lake, far the demand of Earth’s oceans.

The third problem involves the fact that there are various ways to form and expend water. It is a commonsense that many chemistry reactions can generate and consume water. Without ruling out such possibility, it is possible that the water in Earth is from such reaction but not the comets. Even if the comets bring some water to Earth, it is the same likely that such water was expended by some reactions. In short, not considering such possible alternatives, the speaker should not show his assertion yet.

In sum, the speaker cannot justify the voting assertion on basis of the scant evidence. To bolster his assertion that the water in Earth's oceans must have originated from comets, he should provide evidence that a comet had stroked Earth after Earth's gravitation became strong enough and it is large enough to provide water to earth to form the oceans. To better evaluate the assertion, I would need to know whether there exist other ways to form water, and how much water is formed by such other ways.