雅思閱讀模擬練習一

Sun sfickleheartmayleaveuscold

25January2007

FromNewScientistPrintEdition.

StuartClark

1There sadimmerswitchinsidethesunthatcausesitsbrightnesstoriseandfallontimescalesofaround100,000years-exactlythesameperiodasbetweeniceagesonEarth.Sosaysaphysicistwhohascreatedacomputermodelofourstar score.

2RobertEhrlichofGeorgeMasonUniversityinFairfax,Virginia,modelledtheeffectoftemperaturefluctuationsinthesun sinterior.Accordingtothestandardview,thetemperatureofthesun scoreisheldconstantbytheopposingpressuresofgravityandnuclearfusion.However,Ehrlichbelievedthatslightvariationsshouldbepossible.

3HetookashisstartingpointtheworkofAttilaGrandpierreoftheKonkolyObservatoryoftheHungarianAcademyofSciences.In2005,Grandpierreandacollaborator,Gáborágoston,calculatedthatmagneticfieldsinthesun scorecouldproducesmallinstabilitiesinthesolarplasma.Theseinstabilitieswouldinducelocalisedoscillationsintemperature.

4Ehrlich smodelshowsthatwhilstmostoftheseoscillationscanceleachotherout,somereinforceoneanotherandbecomelong-livedtemperaturevariations.Thefavouredfrequenciesallowthesun scoretemperaturetooscillatearounditsaveragetemperatureof13.6millionkelvinincycleslastingeither100,000or41,000years.Ehrlichsaysthatrandominteractionswithinthesun smagneticfieldcouldflipthefluctuationsfromonecyclelengthtotheother.

5ThesetwotimescalesareinstantlyrecognisabletoanyonefamiliarwithEarth siceages:forthepastmillionyears,iceageshaveoccurredroughlyevery100,000years.Beforethat,theyoccurredroughlyevery41,000years.

6MostscientistsbelievethattheiceagesaretheresultofsubtlechangesinEarth sorbit,knownastheMilankovitchcycles.OnesuchcycledescribesthewayEarth sorbitgraduallychangesshapefromacircletoaslightellipseandbackagainroughlyevery100,000years.ThetheorysaysthisalterstheamountofsolarradiationthatEarthreceives,triggeringtheiceages.However,apersistentproblemwiththistheoryhasbeenitsinabilitytoexplainwhytheiceageschangedfrequencyamillionyearsago.

7 "InMilankovitch,thereiscertainlynogoodideawhythefrequencyshouldchangefromonetoanother,"saysNeilEdwards,aclimatologistattheOpenUniversityinMiltonKeynes,UK.NoristhetransitionproblemtheonlyonetheMilankovitchtheoryfaces.EhrlichandothercriticsclaimthatthetemperaturevariationscausedbyMilankovitchcyclesaresimplynotbigenoughtodriveiceages.

8However,EdwardsbelievesthesmallchangesinsolarheatingproducedbyMilankovitchcyclesarethenamplifiedbyfeedbackmechanismsonEarth.Forexample,ifseaicebeginstoformbecauseofaslightcooling,carbondioxidethatwouldotherwisehavefounditswayintotheatmosphereaspartofthecarboncycleislockedintotheice.ThatweakensthegreenhouseeffectandEarthgrowsevencolder.

9AccordingtoEdwards,thereisnolackofsuchmechanisms. "Ifyouaddtheireffectstogether,thereismorethanenoughfeedbacktomakeMilankovitchwork,"hesays. "Theproblemnowisidentifyingwhichmechanismsareatwork."ThisiswhyscientistslikeEdwardsarenotyetreadytogiveuponthecurrenttheory. "Milankovitchcyclesgiveusiceagesroughlywhenweobservethemtohappen.Wecancalculatewhereweareinthecycleandcompareitwithobservation,"hesays. "Ican tseeanywayoftesting[Ehrlich s]ideatoseewhereweareinthetemperatureoscillation."

10Ehrlichconcedesthis. "Ifthereisawaytotestthistheoryonthesun,Ican tthinkofonethatispractical,"hesays.That sbecausevariationover41,000to100,000yearsistoogradualtobeobserved.However,theremaybeawaytotestitinotherstars:reddwarfs.Theircoresaremuchsmallerthanthatofthesun,andsoEhrlichbelievesthattheoscillationperiodscouldbeshortenoughtobeobserved.Hehasyettocalculatethepreciseperiodortheextentofvariationinbrightnesstobeexpected.

11NigelWeiss,asolarphysicistattheUniversityofCambridge,isfarfromconvinced.HedescribesEhrlich sclaimsas"utterlyimplausible".EhrlichcountersthatWeiss sopinionisbasedonthestandardsolarmodel,whichfailstotakeintoaccountthemagneticinstabilitiesthatcausethetemperaturefluctuations.

(716words)

Questions1-4

CompleteeachofthefollowingstatementswithOneorTwonamesofthescientistsfromtheboxbelow.

WritetheappropriatelettersA-Einboxes1-4onyouranswersheet.

1. ...claimsthere『sadimmerswitchinsidethesunthatcausesitsbrightnesstoriseandfallinperiodsaslongasthosebetweeniceagesonEarth.

2. ...calculatedthattheinternalsolarmagneticfieldscouldproduceinstabilitiesinthesolarplasma.

3. ...holdsthatMilankovitchcyclescaninducechangesinsolarheatingonEarthandthechangesareamplifiedonEarth.

4. ...doesn tbelieveinEhrlich sviewpointsatall.

Questions5-9

Dothefollowingstatementsagreewiththeinformationgiveninthereadingpassage?

Inboxes5-9onyouranswersheetwrite

TRUEifthestatementistrueaccordingtothepassage

FALSEifthestatementisfalseaccordingtothepassage

NOTGIVENiftheinformationisnotgiveninthepassage

5.Theiceageschangedfrequencyfrom100,000to41,000yearsamillionyearsago.

6.ThesoleproblemthattheMilankovitchtheorycannotsolveistoexplainwhytheiceagefrequencyshouldshiftfromonetoanother.

7.Carbondioxidecanbelockedartificiallyintoseaicetoeliminatethegreenhouseeffect.

8.SomescientistsarenotreadytogiveuptheMilankovitchtheorythoughtheyhaven tfiguredoutwhichmechanismsamplifythechangesinsolarheating.

9.BothEdwardsandEhrlichbelievethatthereisnopracticalwaytotestwhenthesolartemperatureoscillationbeginsandwhenends.

Questions10-14

Completethenotesbelow.

ChooseonesuitablewordfromtheReadingPassageaboveforeachanswer.

Writeyouranswersinboxes10-14onyouranswersheet.

Thestandardviewassumesthattheopposingpressuresofgravityandnuclearfusionsholdthetemperature...10...inthesun sinterior,buttheslightchangesintheearth s...11...alterthetemperatureontheearthandcauseiceagesevery100,000years.ABritishscientist,however,challengesthisviewbyclaimingthattheinternalsolarmagnetic...12...caninducethetemperatureoscillationsinthesun sinterior.Thesun scoretemperatureoscillatesarounditsaveragetemperaturein...13...lastingeither100,000or41,000years.Andthe...14...interactionswithinthesun smagneticfieldcouldflipthefluctuationsfromonecyclelengthtotheother,whichexplainswhytheiceageschangedfrequencyamillionyearsago.

Answerkeysandexplanations:

1.E

Seethesentencesinparagraph1(There sadimmerswitchinsidethesunthatcausesitsbrightnesstoriseandfallontimescalesofaround100,000years-exactlythesameperiodasbetweeniceagesonEarth.Sosaysaphysicistwhohascreatedacomputermodelofourstar score.)andpara.2 (RobertEhrlichofGeorgeMasonUniversityinFairfax,Virginia,modelledtheeffectoftemperaturefluctuationsinthesun sinterior.)

2.AB

Seepara.3: ?istyle= mso-bidi-font-style:normal >Grandpierreandacollaborator,Gáborágoston,calculatedthatmagneticfieldsinthesun scorecouldproducesmallinstabilitiesinthesolarplasma.

3.C

Seepara.8:EdwardsbelievesthesmallchangesinsolarheatingproducedbyMilankovitchcyclesarethenamplifiedbyfeedbackmechanismsonEarth.

4.D

Seepara.11:NigelWeiss,asolarphysicistattheUniversityofCambridge,isfarfromconvinced.HedescribesEhrlich sclaimsas"utterlyimplausible".

5.False

Seepara.5:forthepastmillionyears,iceageshaveoccurredroughlyevery100,000years.Beforethat,theyoccurredroughlyevery41,000years.

6.False

Seepara.7: "InMilankovitch,thereiscertainlynogoodideawhythefrequencyshouldchangefromonetoanother," ...NoristhetransitionproblemtheonlyonetheMilankovitchtheoryfaces.

7.NotGiven

Seepara.8:ifseaicebeginstoformbecauseofaslightcooling,carbondioxide?islockedintotheice.Thatweakensthegreenhouseeffect. (Thepassagedoesn抰mentionanythingaboutlockingCo2intoiceartificially.)

8.True

Seepara.9:thereisnolackofsuchmechanisms. "Ifyouaddtheireffectstogether,thereismorethanenoughfeedbacktomakeMilankovitchwork,"?"Theproblemnowisidentifyingwhichmechanismsareatwork."ThisiswhyscientistslikeEdwardsarenotyetreadytogiveuponthecurrenttheory.

9.True

Seethesentencesinpara.9 (AccordingtoEdwards, 卙esays. "Ican tseeanywayoftesting[Ehrlich s]ideatoseewhereweareinthetemperatureoscillation.")andpara.10 (Ehrlichconcedesthis. "Ifthereisawaytotestthistheoryonthesun,Ican tthinkofonethatispractical).

10.constant

Seepara.2:Accordingtothestandardview,thetemperatureofthesun scoreisheldconstantbytheopposingpressuresofgravityandnuclearfusion.

11.orbit

Seepara.6:MostscientistsbelievethattheiceagesaretheresultofsubtlechangesinEarth sorbit, 匛arth sorbitgraduallychangesshapefromacircletoaslightellipseandbackagainroughlyevery100,000years.

12.instabilities

Seepara.3: ?istyle= mso-bidi-font-style:normal >magneticfieldsinthesun scorecouldproducesmallinstabilitiesinthesolarplasma.Theseinstabilitieswouldinducelocalisedoscillationsintemperature.

13.cycles

Seepara.4: …allowthesun scoretemperaturetooscillatearounditsaveragetemperatureof13.6millionkelvinincycleslastingeither100,000or41,000years.

14.random

Seepara.4:Ehrlichsaysthatrandominteractionswithinthesun smagneticfieldcouldflipthefluctuationsfromonecyclelengthtotheother.

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