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1、2019高考英语（人教）一轮预热自练题必修2U3及答案**阅读理解OldFossilsScientistshavefoundwhattheythinkisprobablytheoldestfossilonEarth,aremnantoflifefrom3.7billionyearsagowhenEarth’sskieswereorangeanditsoceansgreen.InanewlymeltedpartofGreenland,Australianscientistsfoundtheleftoverstructurefromacom
2、munityofmicrobes（微生物）thatlivedonanancientseafloor.Basedontheiranalysisofthefossils,theresearchersdeterminedthattheyare220millionyearsolderthanthosediscoveredinWesternAustralia,whichwere3.48billionyearsold.Thediscoveryshowslifemayhaveformedquickerandmoreeasilythanoncethou
3、ght,abouthalfabillionyearsafterEarthformed.Andthatmayalsogivehopeforlifeformingelsewhere,suchasMars,saidstudyco-authorMartinVanKranendonkoftheUniversityofNewSouthWalesanddirectoroftheAustralianCenterforAstrobiology.＂Itgivesusanideahowourplanetevolvedandhowlifegainedafoot
4、hold,＂VanKranendonksaid.ScientistshadthoughtitwouldtakeatleasthalfabillionyearsforlifetoformafterthemoltenEarthstartedtocoolabit,butthisshowsitcouldhavehappenedquicker,hesaid.That’sbecausethenewlyfoundfossilisfartoocomplextohavedevelopedsoonaftertheplanet’sfirstlifeforms
5、,hesaid.Inanoutcropofrocksthatusedtobecoveredwithiceandsnowwhichmeltedafteranexceptionallywarmspring,theAustralianteamfoundstromatolites（叠层石）,whicharelayeredstructuresthatareoftenproducedbyacommunityofmicrobes.Thestromatoliteswereabout1to4centimetershigh.＂Itislikethehous
6、eleftbehindmadebythemicrobes,＂VanKranendonksaid.＂Scientistsusedthelayersofashfromvolcanoesandtinyzircon（锆石）withuraniumandestimatedthattheydatebackto3.7billionyearsago.＂Thedatingseemsaboutright,saidAbigailAllwood,aNASAastrobiologistwhofoundthepreviousoldestfossil,from3.48
7、billionyearsago,inAustralia.ButAllwoodsaidsheisnotcompletelyconvinced第1页thatwhatVanKranendonk’steamfoundoncewasalive.Shesaidtheevidencewasn’tconclusiveenoughthatitwaslifeandnotageologicquirk（地质巧合）.＂Itwouldbenicetohavemoreevidence,butintheserocksthat’salottoask,＂Allwoodsa
8、idinanemail.1.Theunderlinedwords＂gainedafoothold＂inParagraph3mean______.A.continuedB.changedC.increased
