Arguement50 【同主题写作第四期】

doris_gxcUID：2370933

1.早期形成时不一定没有水
2.彗星撞击不一定是水的成因（没撞，彗星成分）
3.其他产生水的可能,如2H2+O2=2H2O

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: 365          TIME: 00:55:36          DATE: 2007-8-7 10:07:50

In this manuscript, the author consider comets collision rather than the collisions happened at the forming period should be the originality of the water in Earth's oceans. In fact, the reasoning flawed in several false assumptions discussed as the follow and the author also neglected other possibilities.

To begin with, it is too absolute to make the conclusion convincing that the forming process can not provide any water. It is entirely possible that that the water did not go off into space, since the gravitation increased at that time, which may retain the water vapor in the atmosphere. Therefore the author false assumed that any water present would have evaporated and gone off into the space. It is also implied in the draft that the gravitation at that was not strong enough to hold the water vapor. But if the gravitation had not increased from then on, it could neither be strong enough to maintain the water generated from the collision of comets. As a result, the uncertain assumptions have weakened the point that those collisions of space rocks can not provide any water.

What is more, the author can neither thoroughly support that it was comets that brought water into the Earth. No evidence provided to indicate the comets collisions have ever happen on Earth. If there is no comets collided on Earth, how can the water originated from comets? Furthermore, even if the collisions have really happened, short of detail of the ingredients composed of comets could also make the statements unpersuasive. Maybe the comets hit on Earth do not have any water on them, although other comets could be entirely composed of ice.

In fact, there exists another possibility which is more likely to become the originality of the water on Earth. Since the water can be yielded from the combination of hydrogen and oxygen, it is possible that those gases originally existed on Earth produced the water under certain conditions. The author's ignorance to take these chemical reactions in to consideration leads to the doubtful conclusion.

In sum, the result conducted by the author is unconvincing due the insufficient reasoning. In order the strengthen it, the author should provide more details about the space rocks and the comets. In addition, he also needs to think about the chemical reaction to eliminate readers' doubt.