問題詳情

V. Reading Comprehension 20%Section AAlthough we can imagine life based on something other than carbon chemistry, we knowof no examples to tell us how such life might arise and survive. We must limit our discussionto life as we know it and the conditions it requires. The most important requirement is thepresence of liquid water, not only as part of the chemical reactions of life, but also as amedium to transport nutrients and wastes within the organism.The water requirement automatically eliminates many worlds in our solar system. Themoon is airless, and although some data suggest ice frozen in the soil at its poles, it has neverhad liquid water on its surface. In the vacuum of the lunar surface, liquid water would boilaway rapidly. Mercury too is airless and cannot have had liquid water on its surface for longperiods of time. Venus has some traces of water vapor in its atmosphere, but it is much too hotfor liquid water to survive. If there were any lakes or oceans of water on its surface when itwas young, they must have evaporated quickly. Even if life began there, no traces would beleft now.The inner solar system seems too hot, and the outer solar system seems too cold. TheJovian planets have deep atmospheres, and at a certain level, they have moderate temperatureswhere water might condense into liquid droplets. But it seems unlikely that life could beginthere. The Jovian planets have no surfaces where oceans could nurture the beginning of life,and currents in the atmosphere seem destined to circulate gas and water droplets from regionsof moderate temperature to other levels that are much too hot or too cold for life to survive.A few of the satellites of the Jovian planets might have suitable conditions for life.Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and mineralsdissolved in that water would provide a rich broth of possibilities for chemical evolution.Nevertheless, Europa is not a promising site to search for life because conditions may nothave remained stable for the billions of years needed for life to evolve beyond themicroscopic stage. If Jupiter’s moons interact gravitationally and modify their orbits, Europamay have been frozen solid at some points in history. Such periods of freezing wouldprobably prevent life from developing.Saturn’s moon Titan has an atmosphere of nitrogen, argon, and methane and may haveoceans of liquid methane and ethane on its surface. The chemistry of life that might crawl orswim on such a world is unknown, but life there may be unlikely because of the temperature.The surface of Titan is a deadly -179 °C(-290°F ). Chemical reactions occur slowly or not atall at such low temperatures, so the chemical evolution needed to begin life may never haveoccurred on Titan.Mars is the most likely place for life in our solar system. The evidence, however, is notencouraging. Meteorite ALH84001 was found on the Antarctic ice in 1984. It was probablypart of debris ejected into space by a large impact on Mars. ALH84001 is important because ateam of scientists studied it and announced in 1996 that it contained chemical and physicaltraces of ancient life on Mars.Scientists were excited too, but being professionally skeptical, they began testing theresults immediately. In many cases, the results did not confirm the conclusion that life onceexisted on Mars. Some chemical contamination from water on Earth has occurred, and somechemicals in the meteorite may have originated without the presence of life. The physicalfeatures that look like fossil bacteria may be mineral formations in the rock.第 7 頁，共 11 頁Spacecraft now visiting Mars may help us understand the past history of water there andpaint a more detailed picture of present conditions. Nevertheless, conclusive evidence mayhave to wait until a geologist in a space suit can wander the dry streambeds of Mars crackingopen rocks and searching for fossils.We are left to conclude that, so far as we know, our solar system is bare of life except forEarth. Consequently, our search for life in the universe takes us to other planetary systems.
41. Which of the following sentences does NOT support the main idea of this passage?
(A) The planet that has the greatest probability for life in the past or now is Mars, butmore investigation is required to draw conclusions.
(B) Although some of the moons that revolve around Saturn and Jupiter have conditionsthat might support life, the evidence contradicts this possibility.
(C) It is too hot for life on the planets near the Sun in the inner solar system and too coldon the planets most removed from the Sun in the outer solar system.
(D) Europa has an ocean under the ice on the surface of the moon, which may containthe chemical combinations required for life to evolve.

參考答案

答案：D
難度：適中0.5
統計：A(0),B(0),C(0),D(0),E(0)

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