【Flyer杀G作文组】7.17-Argument50-By CC

师大菜菜UID: 2838404

TOPIC: ARGUMENT50 - 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."
WORDS: 349
TIME: 00:30:00
DATE: 2010/7/16 13:59:28

The speaker asserts that the water in Earth's oceans must have originated from comets. To support the assertion, the author assumes that comets are largely ice made up of frozen water and gases.
After Earth approaching its current size, if a comet strikes Earth, Earth's gravitation will hold gases and water vapor around it as atmosphere. As a result, water vapor will fall as rain on the cooled and solidified surface of Earth. However, after carefully analyzing, I find out many logical fallacies in the argument which will be discussed as follow.

To begin with, the author falsely assumes that there were sufficient amount of comets striking the earth at the critical stage of ocean formation. The author’s conclusion is based on the assumption that there were comets striking the earth after Earth approaching its current size. However, it is entirely possible that the striking had never happened since Earth had approached its current size. For that matter, Earth’s gravitation would not strong enough to hold gases and water vapor around it. The author’s deduction is also not convincing based on the assumption. Without additional evidence to prove the assumption, I cannot accept the author’s conclusion.


What's more, even if the assumption as mentioned above is true, the speaker still fails to convince us that the ice contained in comets could have formed the water in the Earth oceans. What the author tells us is only that the water vapor would be hold around Earth as its atmosphere. But no evidence could ensure the ice contained in comets turned to water vapor which was hold by Earth. It is possible that the ice contained in comets diffused in the space rather than forming the water in the Earth oceans. It is also possible that the ice evaporated. Without ruling out these possibilities, the author cannot convince me that the water in Earth’s oceans originated from comets.

Last but not least, the author fails to take into account other possible originations of the Earth's oceans. The likelihood cannot be excluded that the chemical reaction among the elements in earth resulted in the appearance of water in the sea. It is also possible that the Earth's oceans were originated from the molten in its surface. Except the chemical reaction, it is also possible that the Earth's oceans were originated from water vapor in space. The speaker fails to rule out these possibilities, so the conclusion cannot be accepted by us.

To sum up, the argument is not convincing as it stands. In order to make the argument more persuasive, the author should give evidence to prove the assumptions that the comets are largely ice made up of frozen water and gases, and comets striking Earth happened after the Earth having approached its current size. What's more, it is also necessary to take account of other possible originations of the Earth's.