2014年6月15日托福考试阅读全真试题（二）

下文中新通小编为大家收集了2014年6月15日托福考试阅读全真试题之The composition of atmosphere，更多托福考试资讯，请关注新通外语托福频道。

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The composition of atmosphere

Generally, the composition of atmosphere in early period was suitable for the advancement of higher living organism, since it provided them with sufficient energy as well as protection, contributing to their appearance and survival during the evolution of the biosystem.

In the early days, the atmosphere was filled with a large amount of carbon dioxide and methane, since the sun is a little dark at first, that is to say, it cannot produce enough heat at that time. However, the carbon dioxide and methane can let the heat stay in earth, preventing it from escaping from the earth, which can be considered as an effective way to give the living things on earth a suitable habitant with reasonable climate. Due to the enough energy and heat on earth, those living things can develop and survive during the process of natural selection.

However, with the time passing by, the bacteria produces the dioxide during the photosynthesis, leading to the accumulation of the dioxide in our planet. And at the same time, the sun became huger and huger, which brought about a lot of heat and sunlight. However, owing to the fact that carbon dioxide and methane on earth occupied declining percentage, the climate or the temperature on earth did not change with comparison of that in the early days. The climate at that time is also suitable for the living things.

Why does the accumulation of the dioxide contribute to the development some plants? For this question, there are two reasons. First, the dioxide can facilitate those plants’ metabolism, letting them storing enough nutrition in bodies and providing some water through other functions. Second, the dioxide can form the ozone layer, playing the role a proctor for plants on earth and stopping some cosmic radiation out of the earth. These two functions benefit plants a lot and finally help out earth to be filled with a variety of amazing living things, just as we see now.

With the consideration of the composition of atmosphere on Mars, though some scholars have done some many research on it and also raise and analyze numerous evidences of the existence it is unlikely that there exists some higher organism living there. If they insist on the opinion that some living things has existed on Mars, they must be the lower organism. Until now, most individuals still believe that our planet-earth is the only one for the higher organism.

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