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  3. In 1995 the Galileo spacecraft captured data about Jupiter’s atmosphere--- namely, the absence of most of the predicted atmosphe

In 1995 the Galileo spacecraft captured data about Jupiter’s atmosphere--- namely, the absence of most of the predicted atmosphe

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问题 In 1995 the Galileo spacecraft captured data about Jupiter’s atmosphere--- namely, the absence of most of the predicted atmospheric water--- that challenged prevailing theories about Jupiter’s structure. The unexpectedness of this finding fits a larger pattern in which theories about planetary composition and dynamics have failed to predict the realities discovered through space exploration. Instead of “normal planets” whose composition could be predicted by theory, the planets populating our solar system are unique individuals whose chemical and tectonic identities were created through numerous contingent events. One implication of this is that although the universe undoubtedly holds other planetary systems, the duplication of the sequence that produced our solar system and the development of life on Earth is highly unlikely.
Recently planetary scientists have suggested that the external preconditions for the development of Earth’s biosphere probably included four paramount contingencies. First, a climate conducive to life on earth depends upon the extraordinarily narrow orbital parameters that define a continuously habitable zone where water can exist in a liquid state. If Earth’s orbit were only 5 percent smaller than it is, temperatures during the early stages of Earth’s history would have been high enough to vaporize the oceans. If the Earth-Sun distance were as little as 1 percent larger, runaway glaciations on Earth about 2 billion years ago would have caused the oceans to freeze and remain frozen to this day.
Second, Jupiter’s enormous mass prevents most Sun-bound comets from penetrating the inner solar system. It has been estimated that without this shield, Earth would have experienced bombardment by comet-sized impactors a thousand times more frequently than has actually been recorded during geological time. Even if Earth’s surface were not actually sterilized by this bombardment, it is unlikely that any but the most primitive life-forms could have survived. This suggests that only planetary system containing both terrestrial planets like Earth and gas giants like Jupiter might be capable of sustaining complex life-forms.
Third, the gravitational shield of the giant outer planets, while highly efficient, must occasionally fail to protect Earth. Paradoxically, while the temperatures required for liquid water exist only in the inner solar system, the key building blocks of life, including water itself, occur primarily beyond the asteroid belt. Thus the evolution of life has depended on a frequency of cometary impacts sufficient to convey water, as well as carbon and nitrogen, from these distant regions of the solar system to Earth while stopping short of an impact magnitude that would destroy the atmosphere and oceans.
Finally, Earth’s unique and massive satellite, the Moon, plays a crucial role in stabilizing the obliquity of Earth’s rotational axis. This obliquity creates the terrestrial seasonality so important to the evolution and diversity of life. Mars, in contrast, has a wildly oscillating tilt and chaotic seasonality, while Venus, rotating slowly backward, has virtually no seasonality at all.
The passage suggests each of the following about water on Earth except:
选项 A、It was conveyed to Earth by comets.
B、It appeared on Earth earlier than did carbon and nitrogen.
C、Its existence in a liquid state is contingent on Earth’s orbital parameters.
D、Much of it came from a part of the solar system where water cannot exit in a liquid state.
E、It is unlikely that there would be much of it available to support life if the gravitational shield of the outer planets did not limit the frequency with which comets strike Earth.
答案B
解析 A．It was conveyed to Earth by comets．水是被彗星带到地球的。
解析：定位到第四段第二句，不选。
B．It appeared on Earth earlier than did carbon and nitrogen．水的出现早于碳和氮。
解析：文章没提，选B。
C．Its existence in a hquid state is contingent on Earth’s orbital parameters．水之所以可以液态存在依赖于地球的轨道参数。
解析：定位到第二段第二句，不选。
D．Much of it came from a part of the solar system where water cannot exit in a liquid state．大部分水来自于水不会以液态存在的地方。
解析：定位到第四段第二句，不选。
E．It is unlikely that there would be much of it available to support life if the gravitational shield of the outer planets did not limit the frequency with which comets strike Earth．如果外部行星的引力屏障没有限制彗星撞击地球的频率的话，就不可能有水来维持生命。
解析：定位到第三段第二句，不选。
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