【Flyer杀G作文组】第十三次作业7月18日Argument50-By afufu1124

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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."


Citing the formation principle of Earth and certain evidence about comets consisting of ice that may vaporize through the process that the comets first strike Earth, then go through the atmosphere, the speaker conclude that the water in Earth’s oceans must have originated from comets. Close scrutiny of each of these facts, however, reveals that none of them lend credible support to the recommendation.

To begin with, the argument assume without justification that comets that consists of ice are likely to vaporize when they are passing through the atmosphere of Earth. The line of reasoning is that because comets are made out of ice they would vaporize in the atmosphere. Nevertheless, there exist the possibility that the ice could interacted with elements in the atmosphere under the extreme high temperature produced by friction that resulting from high speed of comets.



Even if the comets transform into water vapor, the water vapor can only take a small part of the existing water vapor retained in the atmosphere on the basis that comets rarely strike Earth in the recorded history. Such low frequency is not sufficient for water vapor, which generated from the collision, to create the entire ocean on Earth.

Moreover, although the heat from collision of space rocks, which form Earth, and made from the increasing gravitational energy of the planet has made any water present evaporate and go off into space, there exists possibility that water vapor in space gather as Earth grew into the current size that can hold gases and water vapor around it as an atmosphere. Except that the speaker can rule out this possibility, it is still questionable to claim that the entire ocean started from water vapor generated from the ice of comets.


On balance, then, the recommendation relies on doubtful assumptions—for example, comets turn into water vapor when they strike Earth—that render it unconvincing as it stands. To strengthen the argument the author would have to demonstrate that water vapor in the atmosphere are from the comets and it form the entire ocean on Earth. Moreover, to bolster the reasoning that mean to exclude the possibility of water vapor could come originally from Earth during its formation, the author must provide compelling evidence that illustrates water vapor as the only source of water vapor in atmosphere. Only by doing so can it be called acceptable explanation of the origin of ocean.