标题: 0910AW 同主题写作第十五期 ARGUMENT50 by iloveusa2009 [打印本页] 作者: iloveusa2009 时间: 2009-8-8 16:35:50 标题: 0910AW 同主题写作第十五期 ARGUMENT50 by iloveusa2009
本帖最后由 iloveusa2009 于 2009-8-8 16:37 编辑
"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."
Based on the fact that comets are largely ice made up of frozen water and gases and the assumption that a comet striking Earth would have vaporized and then the resulting water vapor would retained as rain on the cooled and solidified surface of Earth,
the author asserts that the water in Earth's oceans must have originated from comets. This argument, however, has several logical flaws which render it unconvincing.
First of all, the author unfairly assumes that the time comets striking Earth is at the same time of Earth being formed out of the collision space rocks. Perhaps, as comets striking on, the surface of Earth had already become cool and solid. In this case, comets striking Earth would not be vaporized let down falling as rain to the ground. Thus, mere fact that comets striking Earth at the time of this planet molten lends scant support to the argument.
Secondly, even if comets stroked Earth at the time of the entire planet molten, the author also fails to provide enough evidence to prove that the water vapor from comets vaporizing will surely fall as rain on the surface of Earth. Perhaps, water vapor from comets had run away in the space before Earth's gravitation became strong enough to hold water vapor around it as an atmosphere. Without ruling out such scenarios, the author cannot convince me that water vapor from comets would surely fall on the Earth.
Thirdly, even though the water vapor from comets eventually falling as rain to the surface of Earth, the author also unfairly concludes that the water in Earth's oceans must have originated from comets. Little information mentioned above can support this conclusion. Common sense tells us that the falling on the ground would contain varieties of elements but not comet’s ingredient only. Without ruling out other possibility about the oceans' origination, the author cannot convince me about that water of oceans must come from comets.
In sum, the argument is unconvincing as it stands. To better strengthen it, the author would provide more information about the time of Earth being formed out of the collision of space rocks and comets striking Earth. To better assess it, we need also to know more evidence about the origination of Earth's oceans.