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9月20号GRE阅读机经解析之长阅读

想要知道刚刚过去的GRE考试中，GRE阅读究竟有什么题目吗?今天小编为考生分享2015年9月20号GRE阅读机经解析之长阅读。更多GRE考试真题请关注前程百利GRE官网。 长阅读

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 \

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

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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 glaciation 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 systems 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

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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 wildly oscillating tilt and chaotic seasonality, while Venus,

rotating slowly backward, has virtually no seasonality at all.

1. The passage is primarily concerned with

A. Enumerating conditions that may have been necessary for a particular development

B. Outlining the conditions under which scientists may be able to predict certain events

C. Explaining how a particular finding affected scientists 'understanding of a phenomenon

D. Suggesting reasons why a particular outcome was more likely to occur than other possible outcomes