【Flyer杀G】小组-7.16 Argument50, by Sean

柏拉图的世界UID: 2581296

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: 49
TIME: 00:05:44
DATE: 2010-7-16 15:43:55

The author concludes that the water in Earth's oceans originated from comets. To justify his/her conclusion, the author mainly provides the events that collision of space rocks on Earth evaporated the water on the Earth's surface, and comets were made up of frozen water and gases. However, his/her reasoning is undermined by several logic flaws.

First of all, the author’s assertion that Earth was being formed by collision of space rocks is partial. He/she simply throws out this assertion without any reasoning or evidence, which brings about many alternative explanations of the formation of Earth. As we know, Earth can sometimes undergo seism, and this may intensively change the arrangement lands and continents. So it has been with winds, which might act on the rocks, eroding or moving them. Supposing Earth was largely shaped by those forced other than collision, there wouldn’t be relevantly enough resulting heat.

The author’s statement that all the water present would be evaporated off seems far too dubious. Maybe the water on the surface of Earth was easy to move away, but it might not be the same the water in deeper spaces in Earth. Since the author tells no more about the mechanisms or details about evaporation of water under that condition, we can fairly suppose that some water would infiltrate the sands and rocks to a enough depth to prevent being evaporated.

Besides, one of the most critical assumptions in the argument is that when the comets hit Earth, Earth was already big enough to retain water in the atmosphere, which, however, is not validated. Author tells nothing about the extent to which can Earth be regarded to gain enough size. Maybe Earth was still in tiny size, thus fails to hold sufficient gravitations to attract water.

Granted that Earth held eligible gravitation to retain water in atmosphere, the author unfairly assumes that water were adequate to form oceans on Earth. Probably comets that visited Earth after it had enough size were very few, and water from them cannot meet volume of the oceans on Earth. Even if the water retained in atmosphere was sufficient, it was still possible that some of that water never dropped on solidified surface of Earth, and there it cannot cover all the oceans. Moreover, the author overlooks other possible origins of water in oceans, such as chemical reactions of matter that already existed on earth.

To sum up, the several links of the author’s reasoning chain are inferior. In order to make his/her conclusion sounder, the author can provide more mechanisms, information or statistics about the process of formation of Earth, comet’s collision on Earth, as well as the oceans on Earth.