0910G[North America Flying] by c_king

c_kingUID: 2664896

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:479         TIME: 01:00:00          DATE: 2009-7-17 22:55:53
According to this argument , the arguer holds an opinion that comet striking is the original reason for the formation of the moist atmosphere , after which living water appear on this planet . To support the conclusion , the arguer points out that the Earth is generated through huge collisions ,including several meets with comets. Furthermore , the earth was getting weight to be mature, at this time , the comets ,made up of hydrate, stroke the Earth and eventually appears water . It seems convincing and reasonable at first glance , but I'm afraid that there are some flaws in it that undermined the validity .
It is widely held belief that  cosmos is originated from the explosion in the  unlimited space , and here comes the Earth ,which is formed out of the collision of space rocks. However , there is insufficient evidence proves that some sort of comets collided with the Earth sometime in history , hence we could not concludes that water on the Earth comes form the comets directly . Comets could hit the earth at any time , before the aggrandizement , during the development of gravitation increasing progress , or even did not meet our planet ever . Therefore , there is no guarantee that comets are the initial cause of the formation of water system .
What' s more , although comets are largely ice made up of frozen water and gases before the collision , yet , after they melt , does the hydrate components actually turned to vapor into the atmosphere? The arguer does not provide us with precise statistics or reliable history records about how was everything changed after the collision , which support  his or her conclusion .   
In addition, the arguer commits a fallacy of hasty generalization . Even if water vapor appeared in the atmosphere at that time as a result of melting of comets after the collision , which is , unwarranted assumption , it does not follow that water , stream ,and the ocean on the Earth must have originated from comets . Changes among certain kinds of chemistry element , fierce activity between continent drift , geographical transformation and diversification on the climate level , taking all these factors into consideration , water could appear on the planet through other possible ways .
In conclusion, the arguer fails to establish a causal relationship between the formation of water and striking of comets with the Earth .To strengthen the argument, the arguer would have to provide evidence that comets hit the relative mature Earth indeed , and it is the hydrate components that transformed into the vapor and water .  To better evaluate the argument, we would need more information about the changes took place in that period of time which have nothing to do with the appearance of water on our planet.