argument50 V6站队 8.11

zehuaUID: 199246

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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.'
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The arguer's conclusion is weak. Even if a comet may have stricken Earth and brought water to it, the water may vaporize into space. And it might not be the only source of water.

First, the arguer unfairly assumes that a comet large enough has stricken Earth. However he provide no direct evidence to prove such a hit. Perhaps there was no such a strike at all, or perhaps even if there was a strike, the comet was so small that it could hardly bring any water to Earth. Without direct evidence of such a strike and the size of that comet, I cannot be convinced with the conclusion.

Furthermore, with evidence that comets are largely ice made up of frozen water and gases, the arguer unfairly assumes that a comet could have stricken Earth, vaporized and the water retained in the atmosphere. However, the arguer fails to provide the exact time of such striking, if it has happened at all. Since Earth was being formed out of the collision of space rocks and was very hot, it is entirely possible that such a striking occurred when Earth has not been cooled enough for water drops to form in the atmosphere. In that event, water vaporized into the atmosphere would eventually go off into space with the overwhelming heat, and leave nothing on Earth. Moreover, since Earth used to be small with little gravitational force, even if temperature on Earth had already been lowered enough for the formation of water drops, perhaps its size is still not large enough to retain water. In that event, even if a comet hit Earth, it would not leave any water on it.

In addition, even if a comet has stricken Earth at a correct time and leave large amounts of water on it, the arguer unfairly assumes that comet striking is the only source of water on Earth. However, there might also be other sources of water. Possibly, the core of Earth used to be fulfilled with water, and was brought to the surface by volcanic eruption, or probably certain chemical reactions have taken place and produced water. Without ruling out these possibilities, it would be hasty to conclude that the only source of water is comet striking.

In sum, the arguer's conclusion is groundless as it stands. To better assess his argument, he would have to provide evidence about the size and time of comet striking on Earth. In addition, he must prove that this is the only source of water, and rule out other possibilities of water on Earth.

zehuaUID: 199246

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