GRE Reading Comprehension

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Source: 91年

Since 1953, many experimental attem-pts to synthesize the chemical consti-tuents of life under "primitive Earth condi-tions" have been performed, but none of the these experiments has produced anything approaching complexity of the simplest organism. They have demonstrated, however, that a variety of the complex molecules currently making up living organisms could have been present in the early ocean and atmosphere, with only one limitation: such molecules are synthesized far less readily when oxygen-containing compounds dominate the atmosphere. Therefore some scientists postulate that the Earth's earliest atmosphere, unlike that of today, was dominated by hydrogen, methane, and ammonia.

From these studies, scientists have concluded that the surface of the primitive Earth was covered with oceans containing the molecules fundamental to life. Although, at present, scientists cannot explain how these relatively small molecules combined to produce larger, more complex molecules, some scientists have precipitously ventured hypotheses that attempt to explain the development, from lager molecules, of the earliest self-duplicating organisms.

Question List: 1 2 3 4

The primary purpose of the passage is to

  • A point out that theories about how life developed on Earth have changed little since 1953
  • B warn of increasing levels of hydrogen, methane, and ammonia in the Earth's atmosphere
  • C describe the development since 1953 of some scientists' understanding of how life began on Earth
  • D demonstrate that the synthesis of life in the laboratory is too difficult for modern technology
  • E describe how primitive atmospheric conditions produced the complex molecules of living organisms

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