TPO41阅读文本及答案解析

Climate of Venus

Earth has abundant water in its oceans but very little carbondioxide in its relatively thin atmosphere. By contrast, Venus is very dry andits thick atmosphere is mostly carbon dioxide. The original atmospheres of bothVenus and Earth were derived at least in part from gases spewed forth, oroutgassed, by volcanoes. The gases that emanate from present-day volcanoes onEarth, such as Mount Saint Helens, are predominantly water vapor, carbondioxide, and sulfur dioxide. These gases should therefore have been importantparts of the original atmospheres of both Venus and Earth. Much of the water onboth planets is also thought to have come from impacts from comets, icy bodiesformed in the outer solar system.

In fact, water probably once dominated the Venusian atmosphere.Venus and Earth are similar in size and mass, so Venusian volcanoes may wellhave outgassed as much water vapor as on Earth, and both planets would have hadabout the same number of comets strike their surfaces. Studies of how starsevolve suggest that the early Sun was only about 70 percent as luminous as itis now, so the temperature in Venus’ early atmosphere must have been quite abit lower. Thus water vapor would have been able to liquefy and form oceans onVenus. But if water vapor and carbon dioxide were once so common in theatmospheres of both Earth and Venus, what became of Earth’s carbon dioxide? Andwhat happened to the water on Venus?

The answer to the first question is that carbon dioxide is stillfound in abundance on Earth, but now, instead of being in the form ofatmospheric carbon dioxide, it is either dissolved in the oceans or chemicallybound into carbonate rocks, such as the limestone and marble that formed in theoceans. If Earth became as hot as Venus, much of its carbon dioxide would beboiled out of the oceans and baked out of the crust. Our planet would soondevelop a thick, oppressive carbon dioxide atmosphere much like that of Venus.

To answer the question about Venus’ lack of water, we must return tothe early history of the planet. Just as on present-day Earth, the oceans ofVenus limited the amount of atmospheric carbon dioxide by dissolving it in theoceans and binding it up in carbonate rocks. But being closer to the Sun thanEarth is, enough of the liquid water on Venus would have vaporized to create athick cover of water vapor clouds. Since water vapor is a greenhouse gas, thishumid atmosphere—perhaps denser than Earth’s present-day atmosphere, but farless dense than the atmosphere that envelops Venus today—would have efficientlytrapped heat from the Sun. At first, this would have had little effect on theoceans of Venus. Although the temperature would have climbed above 100° C, theboiling point of water at sea level on Earth, the added atmospheric pressurefrom water vapor would have kept the water in Venus’ oceans in the liquidstate.

This hot and humid state of affairs may have persisted for severalhundred million years. But as the Sun’s energy output slowly increased overtime, the temperature at the surface would eventually have risen above 374°C.Above this temperature, no matter what the atmospheric pressure. Venus’ oceanswould have begun to evaporate, and the added water vapor in the atmospherewould have increased the greenhouse effect. This would have made thetemperature even higher and caused the oceans to evaporate faster, producingmore water vapor. That, in turn, would have further intensified the greenhouseeffect and made the temperature climb higher still.

Once Venus’ oceans disappeared, so did the mechanism for removingcarbon dioxide from the atmosphere. With no oceans to dissolve it, outgassedcarbon dioxide began to accumulate in the atmosphere, intensifying thegreenhouse effect even more Temperatures eventually became high enough to"bake out” any carbon dioxide that was trapped in carbonate rocks. Thisliberated carbon dioxide formed the thick atmosphere of present-day Venus. Overtime, the rising temperatures would have leveled off, solar ultravioletradiation having broken down atmospheric water vapor molecules into hydrogenand oxygen. With all the water vapor gone, the greenhouse effect would nolonger have accelerated.

Paragraph 1

Earth has abundant water in its oceans but very little carbondioxide in its relatively thin atmosphere. By contrast, Venus is very dry andits thick atmosphere is mostly carbon dioxide. The original atmospheres of bothVenus and Earth were derived at least in part from gases spewed forth, oroutgassed, by volcanoes. The gases that emanate from present-day volcanoes onEarth, such as Mount Saint Helens, are predominantly water vapor, carbondioxide, and sulfur dioxide. These gases should therefore have been importantparts of the original atmospheres of both Venus and Earth. Much of the water onboth planets is also thought to have come from impacts from comets, icy bodiesformed in the outer solar system.

1. According to paragraph 1, in what major respect are Venus andEarth different from each other?

A. Whether carbon dioxide v/as present in their originalatmospheres

B. How thin their original atmospheres were

C. What their present-day atmospheres mainly consist of

D. How long ago they first developed an atmosphere

2. Why does the author mention "present-day volcanoes on Earth"?

A. To provide an example of an important difference betweenpresent-day Venus and present-day Earth

B. To help explain why Earth's atmosphere still contains traces ofsulfur dioxide but Venus' does not

C. To indicate one source of information about the likelycomposition of the original atmospheres of Venus and Earth

D. To account for the fact that Earth’s water supply no longer comesprimarily from impacting comets

Paragraph 2

In fact, water probably once dominated the Venusian atmosphere.Venus and Earth are similar in size and mass, so Venusian volcanoes may wellhave outgassed as much water vapor as on Earth, and both planets would have hadabout the same number of comets strike their surfaces. Studies of how starsevolve suggest that the early Sun was only about 70 percent as luminous as itis now, so the temperature in Venus’ early atmosphere must have been quite abit lower. Thus water vapor would have been able to liquefy and form oceans onVenus. But if water vapor and carbon dioxide were once so common in theatmospheres of both Earth and Venus, what became of Earth’s carbon dioxide? Andwhat happened to the water on Venus?

3. According to paragraph 2, what is one reason for thinking that atone time, there were significant amounts of water on Venus?

A. Because of Venus’ size and mass, its volcanoes probably producedmuch more water vapor than volcanoes on Earth did.

B. The low temperature of Venus' early atmosphere can be explainedonly by the presence of water.

C. The presence of carbon dioxide in a planet's atmosphere isan indicator of water on that planet.

D. Venus probably was struck by roughly as many comets as Earth was.

4. The word “luminous” in the passage is closest in meaning to

A. dense

B. bright

C. large

D. active

Paragraph 3

The answer to the first question is that carbon dioxide is stillfound in abundance on Earth, but now, instead of being in the form ofatmospheric carbon dioxide, it is either dissolved in the oceans or chemicallybound into carbonate rocks, such as the limestone and marble that formed in theoceans. If Earth became as hot as Venus, much of its carbon dioxide would beboiled out of the oceans and baked out of the crust. Our planet would soondevelop a thick, oppressive carbon dioxide atmosphere much like that of Venus.

5. Which of the sentences below best expresses the essentialinformation in the highlighted sentence in the passage? Incorrect choiceschange the meaning in important ways or leave out essential information.

A. The first question to be answered is how Earth’s atmosphericcarbon dioxide either got dissolved in the oceans or got chemically bound intocarbonate rocks.

B. The fact that Earth’s abundant carbon dioxide is more often foundin carbonate rock than dissolved in the oceans is the answer to the firstquestion.

C. Earth still has abundant carbon dioxide, but instead of being inthe atmosphere it is now dissolved in the oceans or chemically bound into oceanrocks.

D. The formation of limestone and marble used up the carbon dioxidethat was dissolved in Earth’s oceans so that only carbon dioxide in atmosphericform remained.

Paragraph 4

To answer the question about Venus’ lack of water, we must return tothe early history of the planet. Just as on present-day Earth, the oceans ofVenus limited the amount of atmospheric carbon dioxide by dissolving it in theoceans and binding it up in carbonate rocks. But being closer to the Sun thanEarth is, enough of the liquid water on Venus would have vaporized to create athick cover of water vapor clouds. Since water vapor is a greenhouse gas, thishumid atmosphere—perhaps denser than Earth’s present-day atmosphere, but farless dense than the atmosphere that envelops Venus today—would have efficientlytrapped heat from the Sun. At first, this would have had little effect on theoceans of Venus. Although the temperature would have climbed above 100° C, theboiling point of water at sea level on Earth, the added atmospheric pressurefrom water vapor would have kept the water in Venus’ oceans in the liquidstate.

6. According to paragraph 4, what is one factor that kept the amountof carbon dioxide in the atmosphere of early Venus relatively low?

A. The presence of water vapor clouds

B. The presence of oceans

C. Rapidly increasing temperatures at ground level

D. Low atmospheric pressures

Paragraph 6

Once Venus’ oceans disappeared, so did the mechanism for removingcarbon dioxide from the atmosphere. With no oceans to dissolve it, outgassedcarbon dioxide began to accumulate in the atmosphere, intensifying thegreenhouse effect even more Temperatures eventually became high enough to"bake out” any carbon dioxide that was trapped in carbonate rocks. Thisliberated carbon dioxide formed the thick atmosphere of present-day Venus. Overtime, the rising temperatures would have leveled off, solar ultravioletradiation having broken down atmospheric water vapor molecules into hydrogenand oxygen. With all the water vapor gone, the greenhouse effect would no longerhave accelerated.

7. The phrase “mechanism for” in the passage is closest in meaningto

A. means of

B. importance of

C. need for

D. benefits of

Paragraph 5

This hot and humid state of affairs may have persisted for severalhundred million years. But as the Sun’s energy output slowly increased overtime, the temperature at the surface would eventually have risen above 374°C.Above this temperature, no matter what the atmospheric pressure. Venus’ oceanswould have begun to evaporate, and the added water vapor in the atmospherewould have increased the greenhouse effect. This would have made thetemperature even higher and caused the oceans to evaporate faster, producingmore water vapor. That, in turn, would have further intensified the greenhouseeffect and made the temperature climb higher still.

8. The word “persisted” in the passage is closest in meaning to

A. improved

B. continued

C. weakened

D. evolved

9. According to paragraph 5, what happens when temperatures riseabove 374°C?

A. Atmospheric pressure begins to decrease.

B. Water vapor disappears from the atmosphere.

C. Water evaporates regardless of atmospheric pressure.

D. More energy is required to evaporate a given volume of water.

Paragraph 6

Once Venus’ oceans disappeared, so did the mechanism for removingcarbon dioxide from the atmosphere. With no oceans to dissolve it, outgassedcarbon dioxide began to accumulate in the atmosphere, intensifying thegreenhouse effect even more Temperatures eventually became high enough to"bake out” any carbon dioxide that was trapped in carbonate rocks. Thisliberated carbon dioxide formed the thick atmosphere of present-day Venus. Overtime, the rising temperatures would have leveled off, solar ultravioletradiation having broken down atmospheric water vapor molecules into hydrogenand oxygen. With all the water vapor gone, the greenhouse effect would nolonger have accelerated.

10. According to paragraph 6, extremely high temperatures increasedthe amount of carbon dioxide in Venus’ atmosphere by

A. increasing the rate which carbon dioxide was outgassed

B. baking out carbon dioxide from carbonate rocks

C. creating additional water vapor

D. replacing the previous mechanisms for removing carbon dioxidewith less effective ones

11. The passage supports the idea that the basic reason that Venusand Earth are now so different from each other is that

A. early Venus had more frequent volcanic outgassing than earlyEarth did

B. early Venus had far less liquid water than early Earth did

C. volcanic activity stopped relatively early on Venus but continuedon Earth

D. Venus is closer to the Sun than Earth is

Paragraph 5

12. Look at the four squares [■] that indicate where the following sentence could be added to thepassage.

This cycle of rising temperatures following an increase ingreenhouse gases is known as the

runaway greenhouse effect.

Where would the sentence best fit? Click on a square [■] to add the sentence to thepassage.

This hot and humid state of affairs may have persisted for severalhundred million years. But as the Sun’s energy output slowly increased overtime, the temperature at the surface would eventually have risen above 374°C.  [■] Above this temperature, no matter what the atmospheric pressure.Venus’ oceans would have begun to evaporate, and the added water vapor in theatmosphere would have increased the greenhouse effect.  [■] This would have made the temperature even higher and caused theoceans to evaporate faster, producing more water vapor.  [■] That, in turn, would have further intensified the greenhouseeffect and made the temperature climb higher still.  [■]

13. Directions: Select from the seven phrases below the 2 phrasesthat correctly characterize early Venus and the 3 phrases that correctlycharacterize present-day Venus. Drag each phrase you select into theappropriate column of the table. Two of the phrases will NOT be used. Thisquestion is worth 3 points.

Drag your answer choices to the spaces where they belong. To removean answer choice, click on it.

To review the passage, click VIEW TEXT.

Early Venus

Present-day Venus

Answer Choices

High percentage of water vapor in the atmosphere

Carbon dioxide present only in atmospheric form

An atmosphere quite similar to that of early Earth

Very dense but relatively cool atmosphere

Completely covered with water

Complete absence of surface water

G.   Essentially stabletemperatures