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

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

游客2025-02-22  21
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] According to the passage, scientists have concluded which of the following from the discovery of the large amount of deuterium found in comets?
选项 A、Comets do not contain enough deuterium to have solely created the Earth’s oceans.
B、Given the ratio of deuterium to ordinary hydrogen in seawater, comets cannot have contributed to the Earth’s oceans.
C、It is likely that comets contain less Xenon than meteorites do.
D、Given the low level of deuterium in the waters of Earth’s oceans, comets cannot be its sole source.
E、Comets now play a greater role in the creation of the Earth’s oceans than was previously thought.
答案 D
解析
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