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  3. THREE THEORIES ABOUT ORIGIN OF LIFE (1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of

THREE THEORIES ABOUT ORIGIN OF LIFE (1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of

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问题                                                 THREE THEORIES ABOUT ORIGIN OF LIFE
    (1) Oxygen and nitrogen are major components of our current atmosphere. But the kinds of hydrogen reactions with other gases that are required to transform simple organic molecules into complex ones are interrupted by oxygen, which combines with hydrogen atoms from other compounds. Therefore, life on Earth must have originated when there was very little oxygen in Earth’s atmosphere. The modern scientific theory of life’s origin was first formulated in the 1920s by Russian scientist Aleksandr Oparin and independently by British scientist J. B. S. Haldane. The assumption that life sprang up from chemical reactions that were initiated in the early atmosphere (oxygen-poor/hydrogen-rich) and came to completion in the early oceans was posited by the Oparin-Haldane hypothesis, as it came to be called. Oparin and Haldane suggested that the hydrogen-containing gases were caused to react with each other to form organic compounds by energy sources such as sunlight and lightning.
    (2) With regard to the view that these complex organic compounds could have begun to shape in Earth’s oceans, some researchers remain skeptical. The probability that the fundamental building blocks of life, formaldehyde (CH2O) and hydrogen cyanide (HCN), even though they were probably available, would have been concentrated sufficiently to allow further reactions to occur was likely small. And the more complex organic compounds that might have formed in this way would not have lasted long in the surface of the ocean environment, because photochemical and thermal reactions would have destroyed them. Therefore, researchers have sought alternative explanations for how complex organic compounds formed.
    (3) There is one possibility that the relevant organic compounds were created in space, and asteroids or comets brought them to Earth, probably as tiny dust particles. Recovered from the stratosphere (an upper region of Earth’s atmosphere), interplanetary dust particles (IDPs) are tiny particles that are known to be extraterrestrial origin. From research, we know that organic compounds, including amino acids, exist in IDPs as well as in some meteorites. It is believed that they form from reactions between charged particles and neutral molecules. Those atoms appear in interstellar dust clouds at very low temperatures—on the order of 200 or more degrees below zero on the Celsius scale. It may seem surprising that organic chemistry could occur in the interstellar environment, but it. is precisely the extremely low temperatures involved that allow complex organic molecules to exist because temperatures are too cold to allow them to decompose.
    (4) [A] It is thought that some of the molecules created in the interstellar environment have survived the collapse of the gas and dust cloud that formed our solar nebula and Sun. [BJ They would have been incorporated into solid materials that condensed out of the nebula and formed asteroids and comets. [C] Such materials might have been delivered to Earth in great quantities during the heavy bombardment period of solar system history, between 4.5 and 3.8 billion years ago. [D]
    (5) The hypothesis that life took place in or around hydrothermal vents (hot springs), where new seafloor is being created along mid-ocean ridges (underwater mountain chains) at the ocean’s bottom is the third theory of life’s origin. Seawater that flows a kilometer or more down through crevices in the rock, is heated, and then rises rapidly back to the surface, and the ridges are cooled. During the process, the water gathers substances such as hydrogen, hydrogen sulfide, and dissolved ferrous iron. When it meets the cold water, the extremely hot (350 degree centigrade) vent water generates a dark plume comprised mostly of iron sulfide, a compound produced by the reaction between ferrous iron and hydrogen sulfide.
    (6)Still, the explanation that submarine hydrothermal vents are a likely place for life to have originated is controversial. In vent systems, there are various types of materials from which organic molecules can be synthesized. However, complex organic molecules are not stable at the high temperatures observed in vents positioned directly on the axis of a ridge. If life did originate at the mid-ocean ridges, it probably did so in cooler, off-axis vents. Some researchers claim that the perfect place for life to have begun would be in some near-freezing surface environment because even the off-axis vents are too warm. The dispute as to whether life originated in a hot or cold environment is unlikely to stop.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
选项 A、In consideration of the extreme cold, decomposition of complex organic molecules in the interstellar environment is astonishing.
B、Extremely cold temperatures prevent organic molecules from decomposing, making organic chemistry possible in the interstellar environment.
C、Although the extreme cold makes complex organic molecules exist, organic chemistry rarely occurs in the interstellar environment.
D、Since one would expect the extreme cold to prevent the formation of complex organic molecules, organic chemistry in the interstellar environment is not understandable.
答案B
解析 本题属于句子简化题，要求找出最符合文中高亮句子主要信息的选项。高亮句意为“有机化学能在星际环境中产生，这似乎令人惊讶，但其实正是由于温度太低，复杂的有机分子才得以生存，因为低温使得这些有机分子无法分解”。B项“极低的温度阻止了有机分子的分解，使得有机化学可能存在于星际环境中”传达出了高亮句子的主要信息，故选。A项“就极寒环境来说，复杂有机分子在星际环境中的分解令人惊讶”错误，高亮句说的是复杂有机分子在低温中无法分解。C项“尽管极寒环境使复杂的有机分子得以存在，但有机化学很少在星际环境中产生”错误，高亮句说的是有机化学能在星际环境中产生(could occur)，而C项的rarely occurs没有根据。D项“由于人们认为极寒环境会阻止复杂有机分子的形成，所以人们对星际环境中存在有机化学是不可理解的”错误，高亮句说的是极寒环境阻止了复杂有机分子的分解，而不是形成。
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