0910G【Try Best】第二小组 argument50 by 许浩杰

许浩杰UID: 2644623

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: 484
TIME: 01:49:18
DATE: 2009-6-15 23:38:25

The speaker asserts the claim that the water in Earth's oceans must have originated from comets. To support his conclusion, the speaker cited that comets are largely ice made up of frozen water and gases and that a comet striking Earth then would have vaporized, as a consequence, the resulting water vapor would have been retained in the atmosphere and falling as rain on the cooled, solidified surface of Earth. At first glance, the reasoning seems very convincing, however, a further closely thinking on this manuscript, we will find how groundless it is. The argument suffers from at least 2 logical flaws.

Firstly, there is no ground reason to get this result that the Earth's gravitation became strong enough to hold the gases and water vapor around as an atmosphere when the planet approached its current size will automatically lead to the water in Earth's oceans must have originated from comets. Consider, for example, the Mars is as big as the Earth, and by the gravitation formula the gravitation around the Mars will be just same to the Earth's. In addition, there are lots of comets striking the Mars as well. However, as we all know, there is no atmosphere around the Mars, not to mention the vaporized water around the Mars. Whether water can exist on a planet depend on many factors, such as the temperature, the distance between the star and planet, and the size of the planet. If the distance between the star and planet is so close that the temperature on the planet is much higher than that of water vaporize. If so, water will not exist on the planet at all. In short, it is unconvincing that the size of the planet will result to the existence of water. This is the fatal part of this argument.

On the other hand, even assuming the atmosphere has formed due to the size of the planet,
the claim asserted by speaker that water in Earth's oceans must have originated from comets is totally groundless. Admittedly, we have to concede that comets are largely ices made up of frozen water and gases, a comet striking Earth then would have vaporized. However, we must reveal the assumption of this phenomenon that the comet must have water, no matter frozen water, liquid or gas water. It is profoundly possible that the water will evaporate and go off into spaces due to the heat from the Sun when the comet is on the way to strike the Earth. In another word, the conclusion the water in the Earth's oceans must have originated from comet is unconvincing for the above reason.

To sum up, the argument is unconvincing as it stands. That the water existence lies on the size of planet lacks of some vital evidences and the cause-and-effect relationship between water on the comet and the water on the Earth are unfortunately valid. The speaker needs more convincing evidences to support his claim.