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50.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.'
In this argument, the arguer concludes that the water in Earth's oceans must have originated from comets. To support the conclusion, the arguer points out that the water was produced by a comet which made up of frozen water and gases and had vaporized after it struck with the earth. However, this alone neither constitutes a logical argument in favor of the conclusion nor provides compelling support making the argument sound. The arguer ignores certain important concerns, which must be addressed to prove. In my point of view, the argument suffers from three flaws.
First of all, there is no evidence to prove that any comet had stricken with Earth. From the arguer' claim, after the earth approached its current size to hold gases and water vapor around it as an atmosphere, the comet had impinged the earth, but we can not conform whether did some comets have stricken the earth. Maybe the parlance about comet striking the earth and then producing the water is just a hypothesis and reason of forming water is another one.
In addition, although the comet is largely ice made up of frozen water and gases, it is not affirmative that these ices can become the water in the earth after it having stricken with the earth. Moreover, it also have no any proof to indicate that the comet had impinged the earth and changed the ice into water. Furthermore, there is another possibility that after the comet had impinged the earth, the ice did not thaw but it flied off the atmosphere and floated in universe, so it is impossible that the water in the earth is originated from comets if that is a real fact.
Finally, there is a antinomy in the arguer' claim that since water in the earth would have evaporated and gone off into space, the water unfrozen by ice from comet can also evaporate and go off into space. Because we do not know when did the comet struck the earth and have no any information to conform, if it happened before the earth approached its final size, the water, maybe, was not originated from comets. In addition, other reason, similarly, can cause water such as chemical reaction of elements and so on. Therefore, we can not arbitrarily conclude that the water in Earth's oceans must have originated from comets because of lacking any impelling evidence .
To sum up, though the argument seem to be plausible, in fact, it is neither sound nor persuasive. Not only does it leave out such key issues, but also cites in the analysis the evidence, which does not lend strong support to what the arguer claims. To make the argument more convincing, the arguer would have to take the following conditions into consideration: find out enough evidence and eliminate other possibilities of seawater's origin. If the argument includes the given factors discussed above, it would have been more thorough and adequate. |
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