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1、Unit2Whatishappinesstoyou一、阅读理解。OldFossilsScientistshavefoundwhattheythinkisprobablytheoldestfossilonEarth,aremnantoflifefrom3.7billionyearsagowhenEarth’sskieswereorangeanditsoceansgreen.InanewlymeltedpartofGreenland,Australianscientistsfoundtheleftoverstructurefromacommu
2、nityofmicrobes(微生物)thatlivedonanancientseafloor.Basedontheiranalysisofthefossils,theresearchersdeterminedthattheyare220millionyearsolderthanthosediscoveredinWesternAustralia,whichwere3.48billionyearsold.Thediscoveryshowslifemayhaveformedquickerandmoreeasilythanoncethought
3、,abouthalfabillionyearsafterEarthformed.Andthatmayalsogivehopeforlifeformingelsewhere,suchasMars,saidstudyco-authorMartinVanKranendonkoftheUniversityofNewSouthWalesanddirectoroftheAustralianCenterforAstrobiology."Itgivesusanideahowourplanetevolvedandhowlifegainedafoothold
4、,"VanKranendonksaid.ScientistshadthoughtitwouldtakeatleasthalfabillionyearsforlifetoformafterthemoltenEarthstartedtocoolabit,butthisshowsitcouldhavehappenedquicker,hesaid.That’sbecausethenewlyfoundfossilisfartoocomplextohavedevelopedsoonaftertheplanet’sfirstlifeforms,hesa
5、id.Inanoutcropofrocksthatusedtobecoveredwithiceandsnowwhichmeltedafteranexceptionallywarmspring,theAustralianteamfoundstromatolites(叠层石),whicharelayeredstructuresthatareoftenproducedbyacommunityofmicrobes.Thestromatoliteswereabout1to4centimetershigh."Itislikethehouseleftb
6、ehindmadebythemicrobes,"VanKranendonksaid."Scientistsusedthelayersofashfromvolcanoesandtinyzircon(锆石)withuraniumandestimatedthattheydatebackto3.7billionyearsago."Thedatingseemsaboutright,saidAbigailAllwood,aNASAastrobiologistwhofoundthepreviousoldestfossil,from3.48billion
7、yearsago,inAustralia.ButAllwoodsaidsheisnotcompletelyconvincedthatwhatVanKranendonk’steamfoundoncewasalive.Shesaidtheevidencewasn’tconclusiveenoughthatitwaslifeandnotageologicquirk(地质巧合)."Itwouldbenicetohavemoreevidence,butintheserocksthat’salottoask,"Allwoodsaidinanemail
8、.1.Theunderlinedwords"gainedafoothold"inParagraph3mean______.A.continuedB.changedC.increasedD.St