评论
打印
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.
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
It can be inferred from the passage that “some scientists” assume which of the following concerning “larger, more complex molecules” (line 20)?
A.The earliest atmosphere was formed primarily of these molecules.
B.Chemical processes involving these molecules proceeded much more slowly under primitive Earth conditions.
C.The presence of these molecules would necessarily precede the existence of simple organisms.
D.Experimental techniques will never be sufficiently sophisticated to produce in the laboratory simple organisms from these chemical constituents.
E.Explanations could easily be developed to explain how simple molecules combined to form these more complex ones.
The author's reaction to the attempts that have been made to explain the development of the first self-duplication organisms can best be described as one of
A.enthusiasm
B.expectation
C.dismay
D.skepticism
E.antipathy
According to the passage, which of the following can be inferred about the process by which the chemical constituents of life were synthesized under primitive Earth conditions?
A.The synthesis is unlikely to occur under current atmospheric conditions.
B.The synthesis is common in modern laboratories.
C.The synthesis occurs more readily in the atmosphere than in the ocean.
D.The synthesis easily produces the most complex organic molecules.
E.The synthesis is accelerated by the presence of oxygen-containing compounds.
