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1、Underthesea***阅读理解。OldFossilsScientistshavefoundwhattheythinkisprobablytheoldestfossilonEarth,aremnantoflifefrom3.7billionyearsagowhenEarth’sskieswereorangeanditsoceansgreen.InanewlymeltedpartofGreenland,Australianscientistsfoundtheleftoverstructurefromacommunityofmi
2、crobes（微生物）thatlivedonanancientseafloor.Basedontheiranalysisofthefossils,theresearchersdeterminedthattheyare220millionyearsolderthanthosediscoveredinWesternAustralia,whichwere3.48billionyearsold.Thediscoveryshowslifemayhaveformedquickerandmoreeasilythanoncethought,ab
3、outhalfabillionyearsafterEarthformed.Andthatmayalsogivehopeforlifeformingelsewhere,suchasMars,saidstudyco-authorMartinVanKranendonkoftheUniversityofNewSouthWalesanddirectoroftheAustralianCenterforAstrobiology.＂Itgivesusanideahowourplanetevolvedandhowlifegainedafootho
4、ld,＂VanKranendonksaid.ScientistshadthoughtitwouldtakeatleasthalfabillionyearsforlifetoformafterthemoltenEarthstartedtocoolabit,butthisshowsitcouldhavehappenedquicker,hesaid.That’sbecausethenewlyfoundfossilisfartoocomplextohavedevelopedsoonaftertheplanet’sfirstlifefor
5、ms,hesaid.Inanoutcropofrocksthatusedtobecoveredwithiceandsnowwhichmeltedafteranexceptionallywarmspring,theAustralianteamfoundstromatolites（叠层石）,whicharelayeredstructuresthatareoftenproducedbyacommunityofmicrobes.Thestromatoliteswereabout1to4centimetershigh.＂Itisliket
6、hehouseleftbehindmadebythemicrobes,＂VanKranendonksaid.＂Scientistsusedthelayersofashfromvolcanoesandtinyzircon（锆石）withuraniumandestimatedthattheydatebackto3.7billionyearsago.＂Thedatingseemsaboutright,saidAbigailAllwood,aNASAastrobiologistwhofoundthepreviousoldestfossi
7、l,from3.48billionyearsago,inAustralia.ButAllwoodsaidshe9isnotcompletelyconvincedthatwhatVanKranendonk’steamfoundoncewasalive.Shesaidtheevidencewasn’tconclusiveenoughthatitwaslifeandnotageologicquirk（地质巧合）.＂Itwouldbenicetohavemoreevidence,butintheserocksthat’salottoas
8、k,＂Allwoodsaidinanemail.1.Theunderlinedwords＂gainedafoothold＂inParagraph3mean______.A.continuedB.changedC.increasedD.Started2.Wecan
