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1、Underthesea***阅读理解。OldFossilsScientistshavefoundwhattheythinkisprobablytheoldestfossilonEarth,aremnantoflifefrom3.7billionyearsagowhenEarth’sskieswereorangeanditsoceansgreen.InanewlymeltedpartofGreenland,Australianscientistsfoundtheleftoverstructurefromamunityofmicrobes（微生物）thatlivedonanancient
2、seafloor.Basedontheiranalysisofthefossils,theresearchersdeterminedthattheyare220millionyearsolderthanthosediscoveredinWesternAustralia,whichwere3.48billionyearsold.Thediscoveryshowslifemayhaveformedquickerandmoreeasilythanoncethought,abouthalfabillionyearsafterEarthformed.Andthatmayalsogivehope
3、forlifeformingelsewhere,suchasMars,saidstudyco-authorMartinVanKranendonkoftheUniversityofNewSouthWalesanddirectoroftheAustralianCenterforAstrobiology.＂Itgivesusanideahowourplanetevolvedandhowlifegainedafoothold,＂VanKranendonksaid.Scientistshadthoughtitwouldtakeatleasthalfabillionyearsforlifetof
4、ormafterthemoltenEarthstartedtocoolabit,butthisshowsitcouldhavehappenedquicker,hesaid.That’sbecausethenewlyfoundfossilisfartooplextohavedevelopedsoonaftertheplanet’sfirstlifeforms,hesaid.Inanoutcropofrocksthatusedtobecoveredwithiceandsnowwhichmeltedafteranexceptionallywarmspring,theAustraliante
5、amfoundstromatolites（叠层石）,whicharelayeredstructuresthatareoftenproducedbyamunityofmicrobes.Thestromatoliteswereabout1to4centimetershigh.＂Itislikethehouseleftbehindmadebythemicrobes,＂VanKranendonksaid.＂Scientistsusedthelayersofashfromvolcanoesandtinyzircon（锆石）withuraniumandestimatedthattheydateb
6、ackto3.7billionyearsago.＂Thedatingseemsaboutright,saidAbigailAllwood,aNASAastrobiologistwhofoundthepreviousoldestfossil,from3.48billionyearsago,inAustralia.ButAllwoodsaidsheisnotpletelyconvincedthatwhatVanKranendonk’steamfoundoncewasalive.Shesaidtheevidencewasn’tconclusiveenoughthatitwaslifeand
7、notageologicquirk（地质巧合）.＂Itwouldbenicetohavemoreevidence,butintheserocksthat’salottoask,＂Allwoodsaidinanemail.1.Theunderlinedwords＂gainedafoothold＂inParagraph3mean______.A.continuedB.changedC.increasedD.Started2.WecanlearnfromPara
