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[学习类] 雅思阅读模拟真题系列3

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2016猴年勋章

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曼拓教育 发表于 2016-12-6 15:02:47
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雅思阅读模拟真题系列3

Sun's fickle heart may leave uscold

1 There's a dimmer switch inside the sun that causes its brightness torise and fall on timescales of around 100,000 years - exactly the same periodas between ice ages on Earth. So says a physicist who has created a computermodel of our star's core.

2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelledthe effect of temperature fluctuations in the sun's interior. According to thestandard view, the temperature of the sun's core is held constant by theopposing pressures of gravity and nuclear fusion. However, Ehrlich believedthat slight variations should be possible.

3 He took as his starting point the work of Attila Grandpierre of theKonkoly Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierreand a collaborator, Gábor ágoston, calculated that magnetic fields in the sun'score could produce small instabilities in the solar plasma. These instabilitieswould induce localised oscillations in temperature.

4 Ehrlich's model shows that whilst most of these oscillations cancel eachother out, some reinforce one another and become long-lived temperaturevariations. The favoured frequencies allow the sun's core temperature tooscillate around its average temperature of 13.6 million kelvin in cycleslasting either 100,000 or 41,000 years. Ehrlich says that random interactionswithin the sun's magnetic field could flip the fluctuations from one cyclelength to the other.

5 These two timescales are instantly recognisable to anyone familiar withEarth's ice ages: for the past million years, ice ages have occurred roughlyevery 100,000 years. Before that, they occurred roughly every 41,000years.

6 Most scientists believe that the ice ages are the result of subtlechanges in Earth's orbit, known as the Milankovitch cycles. One such cycledescribes the way Earth's orbit gradually changes shape from a circle to aslight ellipse and back again roughly every 100,000 years. The theory says thisalters the amount of solar radiation that Earth receives, triggering the iceages. However, a persistent problem with this theory has been its inability toexplain why the ice ages changed frequency a million years ago.

7 "In Milankovitch, there is certainly no good idea why the frequencyshould change from one to another," says Neil Edwards, a climatologist atthe Open University in Milton Keynes, UK. Nor is the transition problem theonly one the Milankovitch theory faces. Ehrlich and other critics claim thatthe temperature variations caused by Milankovitch cycles are simply not bigenough to drive ice ages.

8 However, Edwards believes the small changes in solar heating produced byMilankovitch cycles are then amplified by feedback mechanisms on Earth. Forexample, if sea ice begins to form because of a slight cooling, carbon dioxidethat would otherwise have found its way into the atmosphere as part of thecarbon cycle is locked into the ice. That weakens the greenhouse effect andEarth grows even colder.

9 According to Edwards, there is no lack of such mechanisms. "If youadd their effects together, there is more than enough feedback to makeMilankovitch work," he says. "The problem now is identifying whichmechanisms are at work." This is why scientists like Edwards are not yet readyto give up on the current theory. "Milankovitch cycles give us ice agesroughly when we observe them to happen. We can calculate where we are in thecycle and compare it with observation," he says. "I can't see any wayof testing [Ehrlich's] idea to see where we are in the temperatureoscillation."

10 Ehrlich concedes this. "If there is a way to test this theory onthe sun, I can't think of one that is practical," he says. That's becausevariation over 41,000 to 100,000 years is too gradual to be observed. However,there may be a way to test it in other stars: red dwarfs. Their cores are muchsmaller than that of the sun, and so Ehrlich believes that the oscillationperiods could be short enough to be observed. He has yet to calculate theprecise period or the extent of variation in brightness to be expected.

11 Nigel Weiss, a solar physicist at the University of Cambridge, is farfrom convinced. He describes Ehrlich's claims as "utterlyimplausible". Ehrlich counters that Weiss's opinion is based on thestandard solar model, which fails to take into account the magneticinstabilities that cause the temperature fluctuations.

(716 words)


Questions 1-4
Complete each of the following statements with One or Twonames of the scientists from the box below.
Write the appropriate letters A-E in boxes 1-4 on your answer sheet.
A. Attila Grandpierre  
B. Gáborágoston  
C. Neil Edwards  
D. Nigel Weiss  
E. Robert Ehrlich
1....claimsthat there is a dimmer switch inside the sun that causes itsbrightness to rise and fall in periods as long as those between ice ages onEarth.
2....calculated that the internal solar magnetic fields could produceinstabilities in the solar plasma.
3....holds that Milankovitch cycles can induce changes in solar heating onEarth and the changes are amplified on Earth.
4....doesn't believe in Ehrlich's viewpoints at all.

Questions 5-9
Do the following statements agree with the information given in thereading passage?
In boxes 5-9 on your answer sheet write
  
TRUE if the statement is trueaccording to the passage  
FALSE if the statement is falseaccording to the passage  
NOT GIVEN if the information isnot given in the passage

5. The ice ages changed frequency from 100,000 to 41,000 years a million yearsago.
6. The sole problem that the Milankovitch theory cannot solve is toexplain why the ice age frequency should shift from one to another.
7. Carbon dioxide can be locked artificially into sea ice to eliminate thegreenhouse effect.
8. Some scientists are not ready to give up the Milankovitch theory thoughthey haven't figured out which mechanisms amplify the changes in solar heating.
9. Both Edwards and Ehrlich believe that there is no practical way to testwhen the solar temperature oscillation begins and when ends.


Questions 10-14
Complete the notes below.
Choose one suitable word from the Reading Passage above for each answer.
Write your answers in boxes 10-14 on your answer sheet.

The standard view assumes that the opposing pressures of gravity and nuclearfusions hold the temperature ...10...in the sun's interior, but the slightchanges in the earth's ...11... alter the temperature on the earth and causeice ages every 100,000 years. A British scientist, however, challenges thisview by claiming that the internal solar magnetic ...12... can induce thetemperature oscillations in the sun's interior. The sun's core temperatureoscillates around its average temperature in ...13... lasting either 100,000 or41,000 years. And the ...14... interactions within the sun's magnetic fieldcould flip the fluctuations from one cycle length to the other, which explainswhy the ice ages changed frequency a million years ago.



Answer keys and explanations:
1. E
See the sentences in paragraph 1(There's a dimmer switch inside the sunthat causes its brightness to rise and fall on timescales of around 100,000years - exactly the same period as between ice ages on Earth. So says aphysicist who has created a computer model of our star's core.) and para.2(Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled theeffect of temperature fluctuations in the sun's interior.)
2. A B
See para.3: Grandpierre and a collaborator, Gáborágoston, calculated thatmagnetic fields in the sun's core could produce small instabilities in thesolar plasma.
3. C
See para.8: Edwards believes the small changes in solar heating producedby Milankovitch cycles are then amplified by feedback mechanisms on Earth.4.DSee para.11: Nigel Weiss, a solar physicist at the University of Cambridge, isfar from convinced. He describes Ehrlich's claims as "utterlyimplausible".
5. False
See para.5: for the past million years, ice ages have occurred roughlyevery 100,000 years. Before that, they occurred roughly every 41,000 years.
6. False
See para.7: "In Milankovitch, there is certainly no good idea why thefrequency should change from one to another," ... Nor is the transitionproblem the only one the Milankovitch theory faces.
7. Not Given
See para.8: if sea ice begins to form because of a slight cooling, carbondioxideis locked into the ice. That weakens the greenhouse effect. (The passagedoes not mention anything about locking CO2 into ice artificially.)
8. True
See para.9: there is no lack of such mechanisms. "If you add theireffects together, there is more than enough feedback to make Milankovitchwork,""The problem now is identifying which mechanisms are atwork." This is why scientists like Edwards are not yet ready to give up onthe current theory.
9. True
See the sentences in para.9 (According to Edwards, he says. "I can'tsee any way of testing [Ehrlich's] idea to see where we are in the temperatureoscillation.") and para.10 (Ehrlich concedes this. "If there is a wayto test this theory on the sun, I can't think of one that is practical).
10. constant
See para.2: According to the standard view, the temperature of the sun'score is held constant by the opposing pressures of gravity and nuclear fusion.
11. orbit
See para.6: Most scientists believe that the ice ages are the result ofsubtle changes in Earth's orbit, Earth's orbit gradually changes shape from acircle to a slight ellipse and back again roughly every 100,000 years.
12. instabilities
See para.3: magnetic fields in the sun's core could produce smallinstabilities in the solar plasma. These instabilities would induce localisedoscillations in temperature.
13. cycles
See para.4: …allow the sun's core temperature to oscillate around itsaverage temperature of 13.6 million kelvin in cycles lasting either 100,000 or41,000 years.
14. random
See para.4: Ehrlich says that random interactions within the sun'smagnetic field could flip the fluctuations from one cycle length to the other.


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