Comets are now known to contain twice as many atoms of deuterium to

游客2024-01-11 50

问题             Comets are now known to contain twice as many atoms of deuterium to
   each atom of ordinary hydrogen found in seawater.  Scientists have also
   discovered that meteorites could not solely have delivered the water in the
Line    ocean, for then the earth’s atmosphere would contain nearly 10 times as much
(5)    xenon as it actually does, given that meteorites carry excess xenon. Hence, the
   best model for the source of the oceans at the moment is a combination of water
   derived from comets and water caught up in the rocky body of the earth as it
   formed. This mixture satisfies both the xenon and deuterium problem, the
   latter especially if the rocky material out near the earth’s present orbit
(10)    collected some regularly composed local water from the solar nebula before they
   accreted to form the earth. New laboratory studies have indicated that the
   water vapor in the solar nebula would have had a low enough proportion of
   deuterium to complement the excess deuterium found in comets. [br] It can be inferred from the passage that one reason scientists consider local water from the solar nebula a necessary ingredient in the earth’s oceans is that

选项 A、it is improbable that enough volume of water from comets existed to fill the earth’s oceans
B、the water from the solar nebula contains less deuterium than sea water
C、the water from the solar nebula existed close enough to the earth to participate in the accretion process
D、without the water from the solar nebula more xenon would otherwise exist in seawater
E、without the water from the solar nebula the earth’s oceans would probably have formed at an earlier time

答案 B

解析

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