Arguement50 同主题写作第四期

Edmond_LIUID: 2327833

50.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: 514

Before asserting that the water in Earth's oceans originated from comets, several flaws must be noticed in the reasoning of the arguer, who oversimplified the process of the origination of water on Earth, and also fails to take some crucial possibilities into consideration.

First of all, the arguer make a great mistake by taking only the existence of water the result of the water on Earth, which means water must come from H2O neglecting the possibility of forming water through the chemical reaction combining hydrogen with oxygen. In the manuscript, the arguer alleges that the water come from outside of the Earth because the water used to exist on the surface of the Earth evaporated. Yet, as long as hydrogen and oxygen still exist on Earth, it is possible to form water without the help from outside, such as comets. Therefore, whether the environment on the surface of the Earth is suitable for the occurrence of the reaction can be a much more important issue rather than from where the water transferred to the surface of the Earth, when dealing with the problem of origination of the water in Earth's ocean.

Moreover, even the water on the surface evaporated and gone off into space when the Earth still had not a gravitation strong enough to hold, the water inside the surface, even in the form of vapor, still existed, thus there lies another possibility that the water used to be inside the Earth, might come out to the surface after the planet approached its current size, which means the water can be held by gravitation even sent out to the surface. The arguer failed to take this possibility into consideration. Therefore even we do not consider the chemical reaction to form water from other elements, it is still possible for the planet to generate surface water without the aid by something like comet.

Last but not least, the assumption of comets as the origination of surface water on Earth is suspicious. The gain of water from comets seems to be too tiny comparing with the large amount of water in the oceans to be the main origination. The arguer didn't provide us the exact ratio of comets made up by frozen water and gases in terms of all the comets reached the Earth. Further more, if a comet melts so early due to its fast speed that the effect from the earth is still not strong enough to hold the vapor from the comet, the vapor will go off into the space as well, making no contribution to the water in the oceans. As a result, the gaining of water from comets may occur only hazardously, and arguably not efficient at all to supply all the water in Earth's ocean.

To sum up, the arguer hardly provided enough evidence to support his opinion, and failed to take all the possibilities thus building up no causal reasoning that seems convincing to me. More details concerned with the issue need to be researched in order to uncover the real origination of the water in the oceans.

[ 本帖最后由 Edmond_LI 于 2007-8-7 08:26 编辑 ]