Argu50 [Shining Sep 作文组] 8.25

Ajax555UID: 2241288

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: 424          TIME: 0:40:34          DATE: 2006-8-26

In this argument, the arguer asserts that the water in earth's oceans must have originated from comets. The arguer indicates that earth was formed out of the collision of space rocks, and comets striking earth bring water to earth. The reasoning seems reasonable on the surface, however, with careful examination, there are several crucial fallacies in the argument.

First of all, the arguer indicates that if earth wants to hold gases and water vapor around it as an atmosphere, earth should approach its current size. There is no evidence in this argument to support the precondition that there were some comets to strike earth after earth has enough gravitation. Comparing with infinite cosmos, earth is too small to be hit by comets easily. It is possible that from earth had enough gravitation until now, no comet hit earth.

Second, there is a serious antinomy in the arguer's reasoning. On one hand, the arguer said when the energy which was produced by striking made the entire planet molten, water present would have evaporated and gone off into space. On the other hand, the arguer allege that when comets vaporized, the resulting water vapor would fall as rain on the cooled and solidified surface of earth. Whether is earth molten or cool? The argument does not give a sure answer of the temperature of earth.  Whether the water vapor would ratain in the atmosphere or flees into space is also uncertain.

Finally, the assertion that the water in earth's oceans must have originated from comets is too cursory. More than 75 percent of earth is covered by water. The amount of water on earth is so enormous that it is impossible that all water in earth's oceans originated from comets. Because comets are not as big as earth, they can not bring so much water to earth. Moreover, it is possible that the water on earth has other causations. For example, there are a lot of hydrogen and oxygen on earth, when earth was formed. With the chemistry reaction, they can change into plentiful water on earth. Hence, the arguer do not prove water on comets is the only source of water on earth.

To sum up, the conclusion lacks of credibility because the analysis does not lend strong support to what the arguer maintains. To strengthen the argument, the arguer would have to give some history evidence to prove that earth had been strike by comets. To better evaluate the argument, we would need some proof that the water on earth has no other sources.