【big fish】3月17日Argument50-by jjooyy

jjooyyUID: 2704028

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: 303          TIME: 00:30:38          DATE: 2010/3/17 20:24:19

The argument mainly describe how Earth's oceans have originated from comets. It seems reasonable at first glance, but is lack of credit after second consideration.

To begin with, it is lack of evidence that when the planet approached its current size, gases and water vapor around it would be hold because of gravitation. It is presumably that those gases or water vapor could partly leave away from Earth if the gravitation is not strong enough. And the others left behind and became the atmosphere on Earth. Also, these substances could be from other comets, rather than around Earth at first. Since no evidence lends credit to the progress , the idea remains to be seen.

Also, just because comets are largely ice made up of frozen water and gases, this does not necessarily mean that those materials would vaporize when striking Earth. Since Earth at that time would not be very hot, in all likelihood, some ice would melt or stay on earth after striking. This would also make it possible for the oceans to form later. Without providing clear evidence, how the substances of comet went is open to doubt.

In addition, the author fails to take water on Earth into account when concluding the originality of oceans. From the munuscript, there were some water vapor around the Earth as atmosphere. Water in Earth may not always be the same state at that time, with the changes of temperature or other factors. For that reason, it is likely that water vapor could eventually fall as rain on the cooled and solidified surface of Earth, just as what the author assumes about the water vapor which is from comet.

In sum, in order to convince others, the argument is supposed to provide more evidence about all the progresses it mentiones. Otherwise, it is unpersuasive, as some ideas are dubious.
我真的很想具体论述一下，可是没有什么可以论述的，不知道还有怎么样的可能性。。。