Climate of Venus
Earth has abundant water in its oceans but very little carbon dioxide in its relatively thin atmosphere. By contrast, Venus is very dry and its thick atmosphere is mostly carbon dioxide. The original atmospheres of both Venus and Earth were derived at least in part from gas spewed forth, or outgasd, by volcanoes. The gas that emanate from prent-day volcanoes on Earth, such as Mount Saint Helens, are predominantly water vapor, carbon dioxide, and sulfur dioxide. The gas should therefore have been important parts of the original atmospheres of both Venus and Earth. Much of the water on both planets is also thought to have come from impacts from comets, icy bodies formed in the outer solar system.中国最大的群岛
According to paragraph 1, in what major respect are Venus and Earth different from each other?
A Whether carbon dioxide was prent in their original atmospheres
B How thin their original atmospheres were
C 加味二妙散What their prent-day atmospheres mainly consist of
D How long ago they first developed an atmosphere
Why does the author mention “prent-day volcanoes on Earth”?
A To provide an example of an important difference between prent-day Venus and prent day Earth
B To help explain why Earth’s atmosphere still contains traces of sulfur dioxide but Venus’ does not
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C To indicate one source of information about the likely composition of the original atmospheres of Venus and Earth
D To account for the fact that Earth’s water supply no longer comes primarily from impacting comets
In fact, water probably once dominated the Venusian atmosphere. Venus and Earth are si
milar in size and mass, so Venusian volcanoes may well have outgasd as much water vapor as on Earth, and both planets would have had about the same number of comets strike their surfaces. Studies of how stars evolve suggest that the early Sun was only about 70 percent as luminous as it is now, so the temperature in Venus' early atmosphere must have been quite a bit lower. Thus water vapor would have been able to liquefy and form oceans on Venus. But if water vapor and carbon dioxide were once so common in the atmospheres of both Earth and Venus, what became of Earth's carbon dioxide? And what happened to the water on Venus?
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According to paragraph 2, what is one reason for thinking that at one time, there were significant amounts of water on Venus?
A Becau of Venus’ size and mass, its volcanoes probably produced much more water vapor than volcanoes on Earth did.
B 跳舞的歌The low temperature of Venus’ early atmosphere can be explained only by the prence of water.
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C The prence of carbon dioxide in a planet’s atmosphere is an indicator of water on that planet.
D Venus probably was struck by roughly as many comets as Earth was.
The answer to the first question is that carbon dioxide is still found in abundance on Earth, but now, instead of being in the form of atmospheric carbon dioxide, it is either dissolved in the oceans or chemically bound into carbonate rocks, such as the limestone and marble that formed in the oceans. If Earth became as hot as Venus, much of its carbon dioxide would be boiled out of the oceans and baked out of the crust. Our planet would soon develop a thick, oppressive carbon dioxide atmosphere much like that of Venus.
Which of the ntences below best express the esntial information in the highlighted ntence in the passage? Incorrect choices change the meaning in important ways or leave out esntial information.
A The first question to be answered is how Earth’s atmospheric carbon dioxide either got dissolved in the oceans or got chemically bound into carbonate rocks.
B The fact that Earth’s abundant carbon dioxide is more often found in carbonate rock than dissolved in the oceans is the answer to the first question.
C Earth still has abundant carbon dioxide, but instead of being in the atmosphere it is now dissolved in the oceans or chemically bound into ocean rocks.
D The formation of limestone and marble ud up the carbon dioxide that was dissolved in Earth’s oceans so that only carbon dioxide in atmospheric form remained.
情人元宵节祝福语To answer the question about Venus' lack of water, we must return to the early history of the planet. Just as on prent-day Earth, the oceans of Venus limited the amount of atmospheric carbon dioxide by dissolving it in the oceans and binding it up in carbonate rocks. But being clor to the Sun than Earth is, enough of the liquid water on Venus would have vaporized to create a thick cover of water vapor cIouds. Since water vapor is
a greenhou gas, this humid atmosphere, perhaps denr than Earth's prent-day atmosphere, but far less den than the atmosphere that envelops Venus today would have efficiently trapped heat from the Sun. At first, this would have had little effect on the oceans of Venus. Although the temperature would have climbed above 100° C, the boiling point of water at a level on Earth, the added atmospheric pressure from water vapor would have kept the water in Venus' oceans in the liquid state.
