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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: 475 TIME: 00:30:00 DATE: 2007-8-6 下午 05:43:08
The argument rashly arrived at the conclusion about the origination of water in Earth's oceans, without considering other alternative source of water and any reliable data, like the water content of the comets and the amount of comets stroke the earth. It also didn't make a proper comparison between the earth and other planets in the solar system.
First, there is no evidence provided in the argument to show how many comets stroke the earth after the earth approached its current size. Because there was no human back then, so no record in ancient history could provide us any clue. However, there may be some geographical clues that provide us facts about the time of collision and the size of the comet. Even if we can find geographical evidences, it's still far from enough for us to conclude. We should ask about how much water did each comet brought and if we could confirm the happening of most of the collision of comets. Without these data, we can not know the total amount of water the comet brought and whether the amount is sufficient to form the ancient ocean.
Second, the argument failed to compare the earth with other planets in the solar system. There are some planets that not only have enough gravitation to hold water vapor and gases, but also have solid surface, like the Mars. How many comets had stroke the Mars? Were there no fewer comets that stroke the Mars than the earth? If the answer is true, then why is the earth the only planet in the solar system to have a beautiful ocean? Before answer all these questions, I can not believe the conclusion in the argument.
Finally, the argument didn't rule out other possible sources of the waters in the ocean of the earth. There are many other opinions about this issue in the academia. An alternative explanation is that the water comes from the rocks that formed the earth. Some of the rocks originally had some water, or some other compound that can form water. During the process of earth evolvement, the water in the rocks finally come out and forms the ocean. There are also some scientists who believe that water came from the lava. There was countless volcano evaporation in the ancient times. Every time of evaporation, some water vapor comes out of the lava and form the rain. So the ocean gradually formed. The argument failed to rule out these alternatives. Even if the waters of the comet do make up some part of the waters in the ocean, we can not say that the water's only origination is the water in the comets.
In conclusion, with out any authentic data and proper comparison, as well as ruling out other alternative source of water, the conclusion in the argument is just a science fiction. |
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