argument50 [米国有米] 1.30作业

绚烂夏花UID: 2245298

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: 438        TIME: 0:30:00          DATE: 2007-1-30

Before concluding that the water in Earth's oceans must have originated from comets, the evidence provided by the author should be taken into careful consideration from several other angles. The author who gives the assumption of the forming of water should have examining other factors which may have affect the conclusion.

First of all , without showing solid evidence, the author of the argument unfairly takes for granted that the Earth was formed out of the collision of space rocks. We know nothing about how the assumption comes out and whether it is true. Other alternative explanations, however, may be responsible for the formation of the earth. For example, the earth may be part of another planet or the earth was originated from a big stone. Who can tell? The origin of the earth is still a controversial topic waiting for addressing; therefore the explanation given by the author cannot serve as a precondition.

Even if the earth is formed in the way as the argument says, is it true any water present would have evaporated and gone off into space at that time? Will the water stay in other forms, say in other kinds of materials such as rocks and lava? It is highly possible because there is water contained in so many things in the world. If these were the case, then the author's assertion is unconvincing.

We might also ask: are there any other ways in which water can be formed other than from the collision of comets? Is it possible that water may come from the inner side of the earth? Or will some physical and chemical reactions or nuclear reactions yield water as production? Or can the water come from the earth’s atmosphere as a result of precipitation? And what about other kinds of universe objects despite comets? can they be the source of the water in the Earth's oceans? We just don't know. Without ruling out these alternative explanations, the author's conclusion is questionable, at best.

Even if the comets are the source of water in the earth, it is possible all the water carried by comets is absorbed by earth’s atmosphere when the comets strike the earth? The author assumes so. But it is highly possible water vaporized may fleet into the outside of the atmosphere. And also the moon may take some of the water from the vaporized comets. The author fails to take them into consideration.

In conclusion, the author's assertion is not credible as have discussed above. In order to convince me, the author should provide warranted evidence and consider a broad cross-section of all the alternative explanations.