2015年10月10日托福阅读真题解析

额外关注。类似流程类文章可以参考TPO18的Lightning.Lightningisabrilliantflashoflightproducedbyanelectricaldischargefromastormcloud.Theelectricaldischargetakescewhentheattractivetensionbetweenaregionofnegativelychargedparticlesandaregionofpositivelychargedparticles essogreatthatthechargedparticlessuddenlyrushtogether.Thecomingtogetheroftheopposiychargedparticlesneutralizestheelectricaltensionandreleasesatremendousamountofenergy,whichweseeaslightning.Theseparationofpositivelyandnegativelychargedparticlestakesceduringthedevelopmentofthestor Theseparationofchargedparticlesthatformsinastormcloudhasasandwich-likestructure.Concentrationsofpositivelychargedparticlesdevelopatthetopandbottomofthecloud,butthemiddleregion esnegativelycharged.Recentmeasurementsmadeinthefieldtogetherwithlaboratorysimulationsofferapromisingexnationofhowthisstructureofchargedparticlesforms.Whathappensisthatsmall(millimeter-tocentimeter-size)pelletsoficeforminthecoldupperregionsofthecloud.Whentheseicepelletsfall,someofthemstrikemuchsmallericecrystalsinthecenterofthecloud.Thetemperatureatthecenterofthecloudisabout-15℃orlower.Atsuchtemperatures,thecollisionbetweentheicepelletsandtheicecrystalscauseselectricalchargestoshiftsothattheicepelletsacquireanegativechargeandtheicecrystals epositivelycharged.Thenupdraftwindcurrentscarrythelight,positivelychargedicecrystalsuptothetopofthecloud.Theheaviernegativelychargedicepelletsarelefttoconcentrateinthecenter.Thisprocessexinswhythetopofthecloud espositivelycharged,whilethecenteresnegativelycharged.Thenegativelychargedregionislarge:severalhundredmetersthickandseveralkilometersindiameter.Belowthislarge,cold,negativelychargedregion,thecloudiswarmerthan-15℃,andatthesetemperatures,collisionsbetweenicecrystalsandfallingicepelletsproducepositivelychargedicepelletsthatthenpopulateasmallregionatthebaseofthecloud.Mostlightningtakescewithinacloudwhenthechargeseparationwithinthecloudcollapses.However,asthestormclouddevelops,thegroundbeneaththecloud positivelychargedandlightningcantakeceintheformofanelectricaldischargebetweenthenegativechargeofthecloudandthepositivelychargedground.Lightningthatstrikesthegroundisthemostlikelytobedestructive,soeventhoughitrepresentsonly20percentofalllightning,ithasreceivedalotofscientificattention.Usinghigh-speedphotography,scientistshavedeterminedthattherearetwostepstotheoccurrenceoflightningfromacloudtotheground.First,achannel,orpath,isformedthatconnectsthecloudandtheground.Thenastrongcurrentofelectronsfollowsthatpathfromthecloudtotheground,anditisthatcurrentthatilluminatesthechannelasthelightningwesee.Theformationofthechannelisinitiatedwhenelectronssurgefromthecloudbasetowardtheground.Whenastreamofthesenegativelychargedelectronscomeswithin100metersofthegrounditismetbyastreamofpositivelychargedparticlesthatcomesupfromtheground.Whenthenegativelyandpositivelychargedstreamsmeet,acompletechannelconnectingthecloudandthegroundisformed.Thechannelisonlyafewcentimetersindiameter,butthatiswideenoughforelectronstofollowthechanneltothegroundinthevisibleformofaflashoflightning.Thestreamofpositiveparticlesthatmeetsthesurgeofelectronsfromthecloudoftenarisesfromatallpointedstructuresuchasametalflagpoleoratower.Thatiswhythesubsequentlightningthatfollowsthecompletedchanneloftenstrikesatallstructure.Onceachannelhasbeenformed,itisusuallyusedbyseverallightningdischarges,eachofthemconsistingofastreamofelectronsfromthecloudmeetingastreamofpositiveparticlesalongtheestablishedpath.Sometimes,however,astreamofelectronsfollowinganestablishedchannelismetbyapositivestreammakinganewpathupfromtheground.Theresultisaforkedlightningthatstrikesthegroundintwoces.光解作用(photodissociation)产生的而那些大量的氧是由植物光合作用(photosynthesis)发Outgassingfromvolcanism,supplementedbygasesproducedduringthelateheavybombardmentofEarthbyhugeasteroids,producedthenextatmosphere,consistinglargelyofnitrogenpluscarbondioxideandinertgases.Amajorpartofcarbon-dioxideemissionssoondissolvedinwaterandbuiltupcarbonatesediments.Researchershavefoundwater-relatedsedimentsdatingfromasearlyas3.8billionyearsago.About3.4billionyearsago,nitrogenformedthemajorpartofthethenstable"secondatmosphere".Aninfluenceoflifehastobetakenintoaccountrathersooninthehistoryoftheatmosphere,becausehintsofearlylife-formsappearasearlyas3.5billionyearsago.HowEarthatthattimemaintainedaclimatewarmenoughforliquidwaterandlife,iftheearlySunputout30%lowersolarradiancethantoday,isapuzzleknownasthe"faintyoungSunparadox".ThegeologicalrecordhowevershowsacontinuallyrelativelywarmsurfaceduringthecompleteearlytemperaturerecordofEarth-withtheexceptionofonecoldglacialphaseabout2.4billionyearsago.InthelateArcheaneonanoxygen-containingatmospherebegantodevelop,apparentlyproducedbyphotosynthesizingcyanobacteria(seeGreatOxygenationEvent),whichhavebeenfoundasstromatolitefossilsfrom2.7billionyearsago.Theearlybasiccarbonisotopy(isotoperatioproportions)verymuchapproximatescurrentconditions,suggestingthatthefundamentalfeaturesofthecarboncyclebecameestablishedasearlyas4billionyearsago.AncientsedimentsintheRepublicofGabondatingfrombetweenabout2,150and2,080millionyearsagoprovidearecordofEarth'sdynamicoxygenationevolution.ThesefluctuationsinoxygenationwerelikelydrivenbytheLomagundicarbonisotopeexcursion.Theconstantre-arrangementofcontinentsbytetectonicsinfluencesthelong-termevolutionoftheatmospherebytransferringcarbondioxidetoandfromlargecontinentalcarbonatestores.oxygendidnotexistintheatmosphereuntilabout2.4billionyearsagoduringtheGreatOxygenationEventanditsappearanceisindicatedbytheendofthebandedironformations.Beforethistime,anyoxygenproducedbyphotosynthesiswasconsumedbyoxidationofreducedmaterials,notablyiron.Moleculesof oxygendidnotstarttoaccumulateintheatmosphereuntiltherateofproductionofoxygenbegantoexceedtheavailabilityofreducingmaterials.Thispointsignifiesashiftfromareducingatmospheretoanoxidizingatmosphere.O2showedmajorvariationsuntilreachingasteadystateofmorethan15%bytheendofthePrecambrian.Thefollowingtimespanfrom541millionyearsagotothepresentdayisthePhanerozoiceon,duringtheearliestperiodofwhich,theCambrian,oxygen-requiringmetazoanlifeformsbegantoappear.Theamountofoxygenintheatmospherehasfluctuatedoverthelast600millionyears,reachingapeakofabout30%around280millionyearsago,significantlyhigherthantoday's21%.Twomainprocessesernchangesintheatmosphere:ntsusecarbondioxidefromtheatmosphere,releasingoxygen.Breakdownofpyriteandvolcaniceruptionsreleasesulfurintotheatmosphere,whichoxidizesandhencereducestheamountofoxygenintheatmosphere.However,volcaniceruptionsalsoreleasecarbondioxide,whichntscanconverttooxygen.Theexactcauseofthevariationoftheamountofoxygenintheatmosphereisnotknown.Periodswithmuchoxygenintheatmosphereareassociatedwithrapiddevelopmentofanimals.Today'satmospherecontains21%oxygen,whichishighenoughforthisrapiddevelopmentofanimals.4、5小时，他们有很多休闲时间。然后比较各个时需要一个比较安定的生活，因此家庭花在家政(household)方面的时间增多，但花在TheStoneAgewasatimethousandsofyearsago,whenhumanslivedincavesandjungles.Lifewassimple,andtherewereonlytwomainthingstodo–toprotectthemselvesfromthewildanimalsandtogatherfood.ItstartedalmostwiththeevolutionofForbothpurposes,peoplemadetoolsfromstone.Theoldeststonetoolthatwehaveasanevidenceisalmost3.4millionyearsold.ItwasfoundinLowerAwashValleyinEthiopia.Stoneswerealsousedtomakefire.Sinceinthosetimes,humansusedstoneforalmosteverythingtheydid,hencethenameStoneAge.Tolookatatimelineofthisperiodclickhere.TheStoneAgewentonforalongtime.ObviouslyinthebeginningoftheStoneAgerockshelterswerethewaytogo.Anysignsoftroubleandthehumanswouldgohidinginthecaves.In ,theBhimbetkarocksheltersshowtheearliestsignsofhumanlifeintheregion.Theyarealmost30,000yearsold.SomeresearchershavediscoveredS