=七月流火=小组第6次小组作业 Argument50 by 12lghscu

lghscuUID: 2552043

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: 436à510
TIME: 00:29:35
DATE: 2009-9-2 20:33:29

The argument presented above for [url=]concluding[/url] that comets are the source of the Earth's oceans, based on the assumption that collision between comets and Earth [url=]transformed[/url] the frozen water and gases contained in comets into water vapor giving rise to Earth's oceans, seems relatively sound. However, a close scrutiny of the line of reasoning reveals several flaws as follows.

In the first place, the author fails to consider the extremely low possibility of comets' collisions with Earth leading to the Earth's oceans. For one thing, it is a common sense that the striking of comets with Earth happened rarely in history. The author provided no information about the collisions after the Earth gravitation became strong enough to hold gases and water vapor. Perhaps there was only several times. For another thing, even if the striking actually [url=]occurred[/url], the frozen water and gases in the form of ice making up the comets might transform into something else rather than gases and water vapor, which are essential to form rain. Particles might be the major substances after collision, playing less vital role in raindrop. Moreover, suppose the foregoing things happened, the relative low number of comets striking Earth could not contribute to the vast volume of Earth's oceans, covering large part of Earth. Therefore, these facets about the collision of comets with Earth lead little credible support to the possible origination of oceans from comets.

In the second place, the balance between the Earth's gravitation and the amount of vapor is another important factor that affects the level of gases and water vapor around Earth at atmosphere. Once Earth comes into a relatively stable size as the current one, the balance would also become [url=]invariable[/url] , at least, in a small range, pointed out by Newton’s Law. So these vapor increased by the occurrence of comets striking with Earth in a short period of time would go off into space due to the unchanging balance. [url=]Consequently[/url] , the balance would prevent the environment at atmosphere from changing, let alone increasing the volume of vapor, and the corresponding water in oceans.

Last but not least, the author is also failing to consider other possible alternative causes of Earth's oceans. It might be the case that the water contained in Earth itself contributed a lot to the formation of oceans. It also might be the case that the oceans partly [url=]stemmed[/url] from chemical reaction resulting in a large amount of water, besides physical [url=]transformation[/url] of gases and water vapor into water. Hydrogen contained in one substance on Earth forms water in combination of oxygen in another. In addition, other space objects might also strike Earth and consequently make a great contribution to Earth's oceans. Hence, without ruling out such possible alternatives, the assertion in the argument seems unconvincing.

To sum up, based on the discussion mentioned above, the author's conclusion
that Earth's oceans have [url=]stemmed[/url] from comets is [url=]unconvincing[/url] as it stands. It could be approved by providing further information about the occurre[url=]nce[/url] of the collisions and by ruling out other possible causes of the oceans.

[微软用户1]concluding




[微软用户2]Transformed



[微软用户3]Occurred



[微软用户4]Invariable



[微软用户5]
Consequently



[微软用户6]Stemmed



[微软用户7]
Transformation



[微软用户8]Stemmed



[微软用户9]
Unconvincing



[微软用户10]
Occurrence