刘文勇ibt黄金阅读123版本：火星上的流水

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1、智课网TOEFL备考资料刘文勇ibt黄金阅读123版本：火星上的流水摘要：最新版刘文勇新托福黄金阅读12.3版本高清PDF格式支持免费下载，一共71篇，包括刘文勇黄金阅读原29篇，下面是刘文勇ibt黄金阅读12.3版本：火星上的流水，希望对大家备考托福阅读考试有所帮助。刘文勇ibt黄金阅读12.3版本：RUNNINGWATERONMARS火星上的流水PhotographicevidencesuggeststhatliquidwateronceexistedingreatquantityonthesurfaceofMars.Two

2、typesofflowfeaturesareseen:runoffchannelsandoutflowchannels.Runoffchannelsarefoundinthesouthernhighlands.Theseflowfeaturesareextensivesystems—sometimeshundredsofkilometersintotallength—ofinterconnecting,twistingchannelsthatseemtomergeintolarger,widerchannels.Theybear

3、astrongresemblancetoriversystemsonEarth,andgeologiststhinkthattheyaredried-upbedsoflong-goneriversthatoncecarriedrainfallonMarsfromthemountainsdownintothevalleys.RunoffchannelsonMarsspeakofatime4billionyearsago(theageoftheMartianhighlands),whentheatmospherewasthicker

4、,thesurfacewarmer,andliquidwaterwidespread.OutflowchannelsareprobablyrelicsofcatastrophicfloodingonMarslongago.Theyappearonlyinequatorialregionsandgenerallydonotformextensiveinterconnectednetworks.Instead,theyareprobablythepathstakenbyhugevolumesofwaterdrainingfromth

5、esouthernhighlandsintothenorthernplains.Theonrushingwaterarisingfromtheseflashfloodslikelyalsoformedtheoddteardrop-shaped“islands”(resemblingtheminiatureversionsseeninthewetsandofourbeachesatlowtide)thathavebeenfoundontheplainsclosetotheendsoftheoutflowchannels.Judgi

6、ngfromthewidthanddepthofthechannels,theflowratesmusthavebeentrulyenormous—perhapsasmuchasahundredtimesgreaterthanthe105tonspersecondcarriedbythegreatAmazonriver.Floodingshapedtheoutflowchannelsapproximately3billionyearsago,aboutthesametimesasthenorthernvolcanicplains

7、formed.SomescientistsspeculatethatMarsmayhaveenjoyedanextendedearlyPeriodduringwhichrivers,lakes,andperhapsevenoceansadorneditssurface.A2003MarsGlobalSurveyorimageshowswhatmissionspecialiststhinkmaybeadelta—afan-shapednetworkofchannelsandsedimentswhereariveronceflowe

8、dintoalargerbodyofwater,inthiscasealakefillingacraterinthesouthernhighlands.Otherresearchersgoevenfurther,suggestingthatthedataprov