雅思考试阅读模拟试题8含答案Word格式文档下载.docx
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isheld
constant
bythe
opposing
pressuresof
gravityandnuclear
fusion.However,Ehrlichbelievedthat
slight
variationsshouldbepossible.
3HetookashisstartingpointtheworkofAttilaGrandpierreoftheKonkoly
Observatory
oftheHungarian
Academy
ofSciences.In,Grandpierreanda
collaborator,Gá
borá
goston,calculated
that
magnetic
fieldsinthesun'
could
produce
smallinstabilitiesinthesolarplasma.Theseinstabilitieswould
induce
localisedoscillationsin
temperature.
4Ehrlich'
smodelshowsthatwhilstmostoftheseoscillationscanceleachotherout,somereinforce
oneanotherandbecomelong-lived
temperature
variations.Thefavouredfrequenciesallowthesun'
to
oscillate
arounditsaveragetemperatureof13.6millionkelvinincycles
lasting
either100,000or41,000years.Ehrlichsaysthat
random
interactionswithinthesun'
fieldcould
flip
thefluctuationsfromonecyclelengthtotheother.
5ThesetwotimescalesareinstantlyrecognisabletoanyonefamiliarwithEarth'
siceages:
forthepastmillionyears,iceageshaveoccurredroughlyevery100,000years.Beforethat,theyoccurredroughlyevery41,000years.
6Mostscientistsbelievethattheiceagesaretheresultof
subtle
changesinEarth'
sorbit,knownastheMilankovitchcycles.OnesuchcycledescribesthewayEarth'
sorbitgraduallychangesshapefroma
circle
toa
ellipse
andbackagainroughlyevery100,000years.Thetheorysaysthisalterstheamountofsolar
radiation
thatEarthreceives,triggeringtheiceages.However,a
persistent
problemwiththistheoryhasbeenits
inability
toexplainwhytheiceageschanged
frequency
amillionyearsago.
7"
InMilankovitch,thereiscertainlynogoodideawhythe
shouldchangefromonetoanother,"
saysNeilEdwards,aclimatologistattheOpenUniversityinMiltonKeynes,UK.Noristhe
transition
problemtheonlyonetheMilankovitchtheoryfaces.Ehrlichandothercriticsclaim
thatthe
variationscausedbyMilankovitchcyclesaresimplynotbigenoughtodriveiceages.
8However,EdwardsbelievesthesmallchangesinsolarheatingproducedbyMilankovitchcyclesarethen
amplified
byfeedbackmechanismsonEarth.Forexample,ifseaicebeginstoformbecauseofa
cooling,carbondioxidethatwouldotherwisehavefounditswayintotheatmosphereaspartofthecarboncycleislockedintotheice.Thatweakensthe
greenhouseeffectandEarthgrowsevencolder.
9AccordingtoEdwards,thereisnolackofsuchmechanisms."
Ifyouaddtheireffectstogether,thereismorethanenoughfeedbacktomakeMilankovitchwork,"
hesays."
Theproblemnowisidentifyingwhichmechanismsareatwork."
ThisiswhyscientistslikeEdwardsarenotyetreadytogiveuponthe
current
theory."
Milankovitchcyclesgiveusiceagesroughlywhenwe
observe
themtohappen.Wecan
calculate
whereweareinthecycleandcompareitwith
observation,"
Ican'
tseeanywayoftesting[Ehrlich'
s]ideatoseewhereweareinthe
oscillation."
10Ehrlichconcedesthis."
Ifthereisawaytotestthistheoryonthesun,Ican'
tthinkofonethatispractical,"
hesays.That'
sbecause
variation
over41,000to100,000yearsistoogradualtobeobserved.However,theremaybeawaytotestitinotherstars:
reddwarfs.Theircoresaremuchsmallerthanthatofthesun,andsoEhrlichbelievesthatthe
oscillation
periodscouldbeshortenoughtobeobserved.Hehasyetto
the
precise
periodorthe
extent
ofvariation
inbrightnesstobeexpected.
11NigelWeiss,asolarphysicistattheUniversityofCambridge,isfarfrom
convinced.HedescribesEhrlich'
sclaimsas"
utterly
implausible"
.EhrlichcountersthatWeiss'
sopinionisbasedonthestandardsolarmodel,whichfailstotakeintoaccountthe
instabilitiesthatcausethe
fluctuations.
（716words）
Questions1-4
CompleteeachofthefollowingstatementswithOneorTwonamesofthescientistsfromtheboxbelow.
Writethe
appropriate
lettersA-Einboxes1-4onyouranswersheet.
A.AttilaGrandpierre
B.Gá
goston
C.NeilEdwards
D.NigelWeiss
E.RobertEhrlich
1....claimsthere抯adimmer
insidethesunthatcausesitsbrightnesstoriseandfallinperiodsaslongasthosebetweeniceagesonEarth.
2....calculated
internal
solar
fiel
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