Argument50 [认真作文互改小组f_ding 作业] A第一次

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"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 substantiate the conclusion, the arguer points out that the earth was molten by the gravitational energy of the planet and the heat from the collision of space rocks which formed the earth, and thus water would have evaporated and gone off into space, however, when the planet approached its current size, its gravitation was strong enough to hold gases and water vapor around it as an atmosphere. In addition, the arguer reasons that a comet striking earth would have vaporized, since comets are largely ice made up of frozen water and gases. The resulting water vapor would have been retained in the atmosphere, finally falling as rain on the cooled and solidified surface of earth. As it stands, the argument suffers from several critical flaws in it.

First of all, the argument is based on a false assumption. The arguer simply assumes that when the comets stroke the earth, the gravitation of which was strong enough to hold gases and water vapor around it as an atmosphere, the resulting water vapor would have been retained in the atmosphere and fall as rain on the cooled and solidified surface of Earth. However, the arguer does not provide any evidence for the collision of comet with Earth. If that collision did not occur, the water in Earth's oceans was not likely to have originated from comets. Moreover, even if comets did strike Earth, the ice in comets did not necessarily converted into water in Earth. The ice might convert into other substance during collision, since the earth and the comet are different bodies. The arguer fails to present evidence for the conversion of ice in comets into water in Earth.

In addition, the arguer contradicts himself in the claim. The arguer claims that the collision of space rocks forced water evaporate and go off into space, meanwhile, he asserts that when comets hit Earth, water vapor was retained in the atmosphere. But there still existed possibility that this water vapor would go off into space rather than being kept in Earth's atmosphere, though Earth was big enough to hold gases and water vapor in its atmosphere.

Finally, the arguer fails to consider several other relevant factors that may contribute to the existence of ocean. The arguer is assertive in that Earth's water was from the comets. As a matter of fact, the water might be formed on Earth by chemical reactions. It is also possible that Earth's water was from the collision of other planets with Earth rather than comets.

To sum up, the conclusion reached in the argument lacks credibility since the evidence cite in the analysis does not lend strong support to what the arguer claims. To make the argument more convincing, the arguer should provide more information concerning the records of comets' collision with Earth. To better evaluate the argument, we need more concrete evidence that Earth's water was from comets, otherwise the argument is logically unacceptable.