9 ppt Assuming a steady state and a 49year lifetime these levels imply natural emissions of 10 Gg year 41 J H Butler et al Nature 399 749 1999 42 P J Fraser unpublished data 43 We estimate emissions of 1 Gg year in Europe in 1999 006 Gg yea ID: 51960
Download Pdf The PPT/PDF document "suggest that preindustrial levels were" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
)suggestthatpreindustriallevelswere1.9ppt.Assumingasteadystateanda4.9-yearlifetime,theselevelsimplynaturalemissionsof10Ggyear41.J.H.Butleretal.,749(1999).42.P.J.Fraser,unpublisheddata.43.Weestimateemissionsof1GgyearinEuropein1999,0.06GgyearinAustraliain1998Ð99,andGgyearinthewesternUnitedStatesin1999(44.S.Karlsdottir,I.S.A.Isaksen,Geophys.Res.Lett.93(2000).45.M.Mayer,C.Wang,M.Webster,R.Prinn,J.Geophys.,22869(2000).46.A.M.Thompson,,1157(1992).47.Y.Wang,D.Jacob,J.Geophys.Res.,31123P.J.Crutzen,P.H.Zimmerman,,136(1991).TheALE,GAGE,andAGAGEprojectsinvolvedsubstantialeffortsbymanypeoplebeyondtheauthorsofthispaper).Initslatestphase(AGAGE),supportcame(andcomes)primarilyfromNASA,withimportantcontribu-tionsfromtheDepartmentofEnvironment,TransportandtheRegions(UnitedKingdom);CommonwealthSci-entiÞcandIndustrialResearchOrganization(Australia);BureauofMeteorology(Australia);andNOAA,amongothers(28December2000;accepted17April2001Publishedonline3May2001;Includethisinformationwhencitingthispaper. NewAgesfortheLastAustralianMegafauna:Continent-WideExtinctionAbout46,000YearsAgoRichardG.Roberts,*TimothyF.Flannery,LindaK.Ayliffe,HiroyukiYoshida,JonM.Olley,GavinJ.Prideaux,GeoffM.Laslett,AlexanderBaynes,M.A.Smith,RhysJones,BartonL.SmithAllAustralianlandmammals,reptiles,andbirdsweighingmorethan100kilograms,andsixofthesevengenerawithabodymassof45to100kilograms,perishedinthelateQuaternary.Thetimingandcausesoftheseextinctionsremainuncertain.Wereportburialagesformegafaunafrom28sitesandinferextinctionacrossthecontinentaround46,400yearsago(95%conÞdenceinterval,51,200to39,800yearsago).OurresultsruleoutextremearidityattheLastGlacialMaximumasthecauseofextinction,butnototherclimaticimpacts;aÒblitzkriegÓmodelofhuman-inducedextinction;oranextendedperiodofanthropogenicecosystemdisruption.Twenty-threeofthe24generaofAustralianlandanimalsweighingmorethan45kg(which,alongwithafewsmallerspecies,constitutedtheªmegafaunaº)wereextinctbythelateQuaternary().Thetimingandcausesofthisenvironmentalcatastrophehavebeendebatedformorethanacentury(4,5withmegafaunalextirpationbeingattributedtotheimpactofthefirsthumancolonizers(5±8),whoarrived564thousandyearsago(ka)(9±13),orclimatechange()[inpartic-ular,increasedaridityattheLastGlacialMaximum(19to23ka)()].Aresolutiontothisdebatehasbeenthwartedbythelackofreliableagesformegafaunalremainsandforthedepositscontainingthesefossils.Thedis-appearanceofonespeciesofgiantbird(nyornisnewtoni)fromthearidandsemi-aridregionsofsoutheasternAustraliahasbeendatedto505ka,onthebasisofsamplesofeggshell(),butnosecureagesforextinctionhavebeenreportedforthegiantmarsupialsorreptiles,whichconstitute22ofthe23extinctgeneraofmegafaunaweighing45kg.Herewepresentburialages,ob-tainedusingopticalandUdatingmethods,fortheremainsofseveralmegafau-naltaxa(mostlygiantmarsupials;seeTable1)discoveredatsiteslocatedinthehumidcoastalfringeanddriercontinentalinteriorofAustraliaandinthemontaneforestofWestPapua(Fig.1),whichwasjoinedtoAustraliabyalandbridgeattimesofloweredglobalsealevel.Mostmajorbiogeographicandclimaticregions,andallfivemaingroupsoffossilsites(),arerepresentedinoursurvey.MostofthesitesinsouthwesternAustraliaarecavesthathaveactedaspitfalltraps, SchoolofEarthSciences,UniversityofMelbourne,Melbourne,Victoria3010,Australia.SouthAustra-lianMuseum,Adelaide,SouthAustralia5000,Austra-LaboratoiredesSciencesduClimatetdelÕEnvironnement,91198Gif-sur-Yvette,France.CommonwealthScientiÞcandIndustrialResearchOrganization(CSIRO)LandandWater,Canberra,ACT2601,Australia.DepartmentofEarthSciences,Uni-versityofCalifornia,Riverside,CA92521,USA.CSIROMathematicalandInformationSciences,Mel-bourne,Victoria3168,Australia.WesternAustralianMuseum,Perth,WesternAustralia6000,Australia.NationalMuseumofAustralia,Canberra,ACT2601,DepartmentofArchaeologyandNaturalHistory,ResearchSchoolofPaciÞcandAsianStudies,AustralianNationalUniversity,Canberra,ACT0200,DepartmentofEarthSciences,LaTrobeUniversity,Melbourne,Victoria3086,Australia.*Towhomcorrespondenceshouldbeaddressed.E-mail:rgrobe@unimelb.edu.auPresentaddress:DepartmentofGeologyandGeo-physics,UniversityofUtah,SaltLakeCity,UT84112, Fig.1.MapoftheAustralianregionshowingthemegafaunasitesdatedinthisstudy.Sitenumbers:1,NedÕsGully;2,MookiRiver;3,CoxÕsCreek(Bando);4,CoxÕsCreek(Kenloi);5,TambarSprings;6,CuddieSprings;7,LakeMenindee(SunsetStrip);8,WillowPoint;9,LakeVictoria(site50);10,LakeVictoria(site51);11,LakeVictoria(site73);12,MontfordÕsBeach;13,LakeWeering;14,LakeCor-angamite;15,LakeWeeranganuk;16,LakeColongulac;17,Warrnambool;18,VictoriaFossilCave(GrantHall);19,Vic-toriaFossilCave(FossilChamber);20,WoodPoint;21,LakeCallabonna;22,DevilÕsLair;23,KudjalYolgahCave;24,MammothCave;25,MoondyneCave;26,TightEntranceCave;27,DuBoulayCreek;28,KelangurrCave.Thebolddashedlinecrossingthecontinentindicatestheap-proximatepresent-dayboundarybe-tweenthezonesdominatedbysummerrainfallfrommonsoonalactivity(northoftheline)andwinterrainfallfromwesterlystormtracks(southoftheline).Thestippledareaindicatesthezonethatreceiveslessthan500mmrainfallperyearandwherepotentialevapotranspirationexceedsmeanmonthlyevapotranspirationyear-roundwithnegligiblerunoff.Climaticdataarefrom(24,38)andreferencestherein.8JUNE2001VOL292SCIENCEwww.sciencemag.org Table1.Megafaunaltaxarepresentedatthestudysites.ThenamesofthenumberedsitesaregiveninTable2andFig.1.Taxarepresentedbyarticulatedremainsareindicatedbywhereasxandcf.denotetaxarepresentedbydisarticulatedremainsorremainsforwhicharticulationisuncertain.ParenthesesindicatethatGenyornisnewtoniisrepresentedbyafootprintatWarrnambool(site17)andbyeggshellatWoodPoint(site20).TheextantM.fuliginosus,andSarcophilusharrisiiareincludedastheyarerepresentedbyindividualsupto30%largerindentaldimensionsthanthelivingforms.ThegiganticformofisreferredtohereasM.g.titan,andthatofS.harrisiiS.h.laniariusWallabiakitcheneribelongtogeneraextantineasternAustraliabutextinctinWesternAustralia. 123456*6789,1011121314151617181920212223242526J26H26D2728Articulatedremainsrepresented...XXXXXXXXX...sp.indet.......x.......................Megalaniaprisca......x.......................Wonambinaracoortensis.......................x......sp.indet.....xx.......................sp.indet.......x.......................Genyornisnewtoni.....xx.........()..(x).........Proguranaracoortensis..................x...........Megalibgwiliaramsayi..................x....xx............................x......Sarcophilusharrisiilaniariusx.........x..x.x..x........x..Diprotodonoptatum.xx..x.....x...........sp.indet.....x........x....x...........Maokopiaronaldi.............................xZygomaturustrilobus.................x......x..sp.indet................x..............Palorchestesazael.x....x...........x...........Phascolonusgigasxx....x....x..............Vombatushacketti.....................xxx...x..Thylacoleocarnifexxx.......x...x.x.x..x.x......Propleopusoscillans..................x...........Borungaboodiehatcheri...........................x..Macropusferragus.............................Macropusfuliginosus.....................xxx....Macropusgiganteustitanx...xx...x...x..........sp.indet.....x............xx...........Procoptodongoliahx......x..................sp.indet.....x..........x..............Protemnodonanak.........x....x..............Protemnodonbrehus............cf.......x...x..Protemnodonhopei.............................xProtemnodonroechus.................x...........sp.indet..x....x.............x........Simosthenurusbaileyi..................x...........Simosthenurusbrownei.......................x..Simosthenurusgilli.................x...........Simosthenurusmaddocki..................x...........Simosthenurusnewtonae.................xx........x..Simosthenurusoccidentalis.....................xx.xxx..Simosthenuruspales..................x........x..sp.indet................x.....x........Sthenurusandersoni.cf....cf....x........x..........Sthenurusatlas.........x....................Sthenurusstirlingi.............................Sthenurustindalei.........x...................sp.indet.......x.x.....x...............Wallabiakitcheneri.......................x...x..*Site6,units5,6a,and6b.Site6,units7to12.www.sciencemag.orgSCIENCEVOL2928JUNE2001 whereasthesitesineasternAustraliaconsistmainlyofaeoliandepositsalongtheedgesofformerorpresentlakebasins,riverorswampdeposits,andcoastaldunedeposits.Tomax-imizeourprospectsofencounteringfossilscloseinagetotheterminalextinctionevent,wechosesitesthatgeomorphologicalandstratigraphicevidenceindicatedwererela-tivelyyoung.Themostrecentmegafaunalsitemaynotbeincludedinoursurvey,butweconsiderthatasufficientnumberofsites(28)havebeendatedtodiscernaclearpatterninthedistributionofburialages.Areview()of91radiocarbon(agesobtainedforAustralianmegafaunabe-fore1995rejectedthevastmajorityofagesasbeingunreliable(),includingallthoseyoungerthan28kabeforethepresent(B.P.).TheremainingCageswereclosetoorbeyondthepracticallimitsofthetechnique,orwereonmaterialsthathadambiguousassociationswiththemegafaunalremains.Radiocarbondatingofboneandcharcoalold-erthan35kaisproblematicusingconven-tionalsamplepretreatments().Conse-Cageswereusedinthisstudyonlyforcomparisonwithagesof50kaobtainedTable2.Opticalagesforburialsediments,supportingdata,andsamplecontexts. Site*SamplecontextGrainsizeDoserate(GykaOpticalage1.NedÕsGullyMegafaunalunit,sample1180Ð2120.760.0935247Megafaunalunit,sample290Ð1250.780.0936346NewSouthWales2.MookiRiverMegafaunalunit90Ð1251.770.16744423.CoxÕsCreek(Bando)Megafaunalunit,sample190Ð1251.430.14#75353Megafaunalunit,sample1180Ð2121.380.14#75354Megafaunalunit,sample290Ð1251.430.14#726504.CoxÕsCreek(Kenloi)5cmabovemegafaunalunit90Ð1250.930.064725130cmbelowmegafaunalunit90Ð1250.970.065125330cmbelowmegafaunalunit180Ð2120.940.06543585.TambarSpringsMegafaunalunit(spit4)90Ð1251.430.092.90.22.06.CuddieSpringsAbovemainmegafaunalunit(unit4)90Ð1252.47Megafaunalunit(unit5)90Ð1252.22Megafaunalunit(unit6a)90Ð1251.95Megafaunalunit(unit6b)90Ð1252.727.LakeMenindee(SunsetStrip)Megafaunalunit180Ð2121.690.091138678.WillowPointAttachedtoMVspecimen90Ð1250.860.08472559.LakeVictoria(site50)AttachedtoMVspecimen180Ð2120.5935210.LakeVictoria(site51)AttachedtoMVspecimen90Ð1250.710.083825411.LakeVictoria(site73)AttachedtoMVspecimen90Ð1251.710.1816559712.MontfordÕsBeachAttachedtoMVspecimen90Ð1250.8313.LakeWeeringAttachedtoMVspecimen90Ð1251.420.15#11738214.LakeCorangamiteAttachedtoMVspecimen,sample190Ð1251.500.1879452AttachedtoMVspecimen,sample1180Ð2121.470.1878453AttachedtoMVspecimen,sample2180Ð2121.460.177044815.LakeWeeranganukAttachedtoMVspecimen180Ð2126.30.7#437187016.LakeColongulacAttachedtoMVspecimen180Ð2121.59108217.WarrnamboolFromMVsedimentslabwithfootprint180Ð2120.610.0837360SouthAustralia18.VictoriaFossilCave(GrantHall)20cmbelowtopofmegafaunalunit90Ð1251.280.0810798419.VictoriaFossilCave(FossilChamber)50cmbelowtopofmegafaunalunit90Ð1250.670.04115617150cmbelowtopofmegafaunalunit180Ð2120.650.04102815720.WoodPointUnitcontainingeggshell90Ð1251.600.14#8835521.LakeCallabonnaAttachedtoMVspecimen90Ð1250.620.0746275WesternAustralia22.DevilÕsLairAbovemainmegafaunalunit(layer28)90Ð1251.220.0551242Megafaunalunit(layer32)90Ð1251.710.07#79347Megafaunalunit(layer39)90Ð1251.350.066524823.KudjalYolgahCaveMegafaunalunit(pit2)90Ð1251.110.0551246AttachedtoWAMspecimen125Ð2501.220.145624624.MammothCaveUppermegafaunalunit90Ð1250.720.0940455AttachedtoWAMspecimen,sample190Ð1251.040.1566263AttachedtoWAMspecimen,sample290Ð1250.900.126737425.MoondyneCaveMegafaunalunit90Ð1250.680.05#89713126.TightEntranceCaveMegafaunalunit(unitJ)90Ð1250.720.0424333Megafaunalunit(unitH)90Ð1250.520.0323345Megafaunalunit(unitD)90Ð1250.730.041031414127.DuBoulayCreekAttachedtoWAMspecimen90Ð1252.7WestPapua28.KelangurrCaveMegafaunalunit90Ð1251.071.016*SiteswithtaxarepresentedbyarticulatedremainsaremarkedbyMVandWAMindicatesedimentremovedfrommegafaunalcollectionsattheMuseumofVictoriaandWesternAustralianMuseum,respectively.uncertainty.SampleswithasigniÞcantdeÞcitofUcomparedtoRaaremarkedby#,andthosewithasigniÞcantexcessofUoverRaaremarkedby¤.Paleodosevaluesinclude2%uncertaintyassociatedwithlaboratorybeta-sourcecalibration.TheCuddieSprings(site6)sampleshavemultiplepaleodosepopulations,ofwhichthehighestareshown().TheMontfordÕsBeach(site12)andDuBoulayCreek(site27)sampleshavepaleodosedistributionsconsistentwithpartialbleaching(),sotheminimumpaleodosevaluesandageestimates[obtainedusingaminimumagemodel()]areshown.ThehighpaleodoseoftheLakeWeeranganuk(site15)samplewasobtainedfromaliquotswithsaturatingexponentialpluslineargrowthcurvesofluminescenceintensityversusdose().Thissamplealsohasanunusuallyhighdoserate,whichisduetoconcentrationsof20ppmofallradionuclidesintheUdecayseries.Iftheseconcentrationswerelowerinthepast,thentheopticalagewouldbeolder.8JUNE2001VOL292SCIENCEwww.sciencemag.org fromopticaldatingofmegafauna-bearingsedimentsandUdatingofflow-stonesformedaboveandbelowmegafaunalremains.Opticaldatingisaluminescence-basedmethodthatindicatesthetimeelapsedsincethesedimentgrainswerelastexposedtosunlight(20±22).Theopticalagecorre-spondstotheburialageofmegafaunalre-mainsinprimarydeposition,whereasUdatinggivesthecrystallizationageoftheflowstone,andthusaconstrainingageforremainsaboveorbelowtheflowstone.Sup-portfortheopticalagesreportedhere(Table2)isprovidedbytheirconsistencywiththeCandUagesobtainedatmegafaunalsiteswherecomparisonshavebeenmade(Table3)(19,23±25).AllthreemethodsyieldconcordantageswithinthetimerangeofCdating,andbeyondthislimittheopticalandUagesareingoodagreementandcorrectstratigraphicOpticalandUdatingwerecon-ductedprimarilyondepositscontainingtheremainsofmegafaunainarticulatedana-tomicalposition(Table1)toavoiduncer-taintiesintroducedbypost-depositionaldisturbanceandreworkingoffossils.ThisconservativeapproachisvitalbecausetheremainsmustbeinprimarydepositionalcontexttoestimatethetimeofdeathfromopticaldatingoftheburialsedimentsorUdatingoftheenclosingflow-stones.Wealsodatedsomedepositswithdisarticulatedremains,butwerecognizethattheseageswillbetooyoungiftheremainshavebeenderivedfromolderunits.Asandstoneslabbearingtheimpres-sionofafootprintanddunesandscontainingburntfragmentsofeggshellwerealsodated.Sedimentsamplesforopticaldatingwerecollectedonsitefromstratigraphicunitsthatwereclearlyrelatedtothemegafaunalremains;inaddition,lumpsofsedimentattachedtomegafaunalremainsinmuseumcollectionswereremovedfordating(Table2).Weadoptedaconservativeapproachtodatingofmuseumsamples(),owingtotheirsmallsizeandthelackofaninsitudoseratemeasurement.Confidenceintheageestimatesforthemuseumspecimensisgiv-enbythecloseagreementbetweentheagesofthemuseumandfield-collectedsamplesfromKudjalYolgahCave(site23;seeTable2).Ourmainconclusions,however,arebasedonfield-collectedsamples,whichyieldthemostreliableandpreciseages.CalciteflowstoneswerepreparedforUdatingusingstandardmethodsandwereanalyzedbythermalionizationmassspectrometry(19,24,25),andtheages(Table3)havebeencorrectedfordetritalThcontamination(Theyoungestopticalagesobtainedfordepositswitharticulatedmegafaunalremains(Table2)()are474kaforNed'sGully(site1)inQueenslandand462kaforKudjalYolgahCave(site23)inWesternAustralia.Thisresultimpliesbroadlysyn-chronousextinctionacrossthecontinent.Claimshavealsobeenmade()forarticu-latedremainsofSimosthenurusoccidentalisofsimilaragefromTightEntranceCave(site26,unitHorbelow)inWesternAustralia,andseveralsites(3,4,8,9,and10)inNewSouthWalesproducedslightlyolderages(50to55ka)forarticulatedmegafauna.Incon-trast,muchyoungerapparentburialageswereobtainedforsomesitescontainingdis-articulatedremains(Table2)();theyoungestsuchageis2.00.2kaforfrag-mentedremainsatTambarSprings(site5).OpticaldatingofindividualgrainsfromtheCuddieSpringsdeposit[site6()]indicatesthatsomesedimentmixinghasoccurred(WeinterprettheyoungagesobtainedfordisarticulatedremainsandtheindicationofsedimentmixingatCuddieSpringsasevi-dencethattheremainsarenotintheirprima-rydepositionalsetting,buthavebeenerodedfromolderunitsandredepositedinyoungerunitswithcontemporaneoussedimentandTheyoungestmeasuredburialageforarticulatedremainsmaybeolderthantheterminalextinctionevent,unlessthemostrecentburialsiteisfortuitouslyincludedinoursurvey.Buteachopticalagehasarelativestandarderrorof5to15%,sothemeasuredagecouldbychancebelessthanthetrueextinctionageatsomesites.Ac-cordingly,webuiltastatisticalmodelofthedataundertheassumptionthatthetrueburialagesarearealizationofaPoissonprocessofconstantintensityuptothetimeofextinction.Thatis,weassumedthatthetrueburialagesaredistributedrandomlythroughtime,withequalnumbersperunittime,onaverage.TheopticalageisthetrueburialageplusaGaussianerrorwithameanofzeroandastandarddeviationequaltothereportedstandarderror.Weestimat-edthetimeofextinctionbymaximumlike-lihood,confiningattentiontoarticulatedremainswithopticalagesof55ka(Thisavoidsapotentialdifficultycausedbytheundersamplingofsitesmucholderthantheextinctionevent.Usingthismodel,themaximumlikelihoodestimateoftheextinc-tiontimeis46.4ka,with68%and95%confidenceintervalsof48.9to43.6kaand51.2to39.8ka,respectively.Ourdatashowlittleevidenceforfaunalattenuation.Twelveofthe20generaofmegafaunarecordedfromPleistocenedepos-itsintemperateAustralia(1,2)survivedtoatleast80ka,includingthemostcommonandwidespreadtaxa,andsixofthesegenera,andarerepresentedatthetwositesdatedtoaround46ka.Thesedataindicatethatarelativelydiversegroupofmegafaunasur-viveduntilclosetothetimeofextinction.Furthersitesareneededtotestthisproposi-tionandtoidentifythecause(s)ofmegafau-nalextinction.Table3.UagesforWesternAustralianßowstones,supportingdata,andsamplecontexts.Thesubscripts()and(0)denotethepresentandinitialvaluesofU,respectively.Allerrorsare2.AgesforßowstonesatDevilÕsLair(site22),TightEntranceCave(site26),andVictoriaFossilCave(GrantHall,site18,andFossilChamber,site19)arereportedelsewhere(24,25,28 Site*SamplecontextDetritalTh(ppm)activityratioactivityratioage(ka)23.KudjalYolgahCaveAbovemegafaunalunit,sample1U0.0080.3020.006102121121413.90.234.7C0.2940.008102311123433.6Abovemegafaunalunit,sample2U0.0080.3310.003105711775.370.0538.5C0.3080.005105181161935.424.MammothCaveAboveuppermegafaunalunitU0.0250.3750.0034935735.950.0547.9C0.3530.0064916561844.4BelowuppermegafaunalunitU0.0560.4570.0057348654.490.0560.0C0.4290.0097222842555.225.MoondyneCaveAbovemegafaunalunitU0.0610.3410.00440445417.70.343.1C0.3350.0084124462742.2*Allthreesiteshavetaxarepresentedbyarticulatedremains.Datacorrected(C)anduncorrected(U)fordetritalThcontamination().Thedetritallycorrectedagesareconsideredmorereliable.www.sciencemag.orgSCIENCEVOL2928JUNE2001 Theburialagesforthelastknownmegafaunaloccurrencesuggestthatextinc-tionoccurredsimultaneouslyineasternandwesternAustralia,andthusprobablyconti-nent-wide,between51and40ka(95%con-fidenceinterval),atleast20kabeforetheheightoftheLastGlacialMaximum.Weestimatethatthemegafaunahadvanishedwithin105kaofhumanarrival[564ka9±13)]acrossawiderangeofhabitatsandclimaticzones.MegafaunalextinctioninAustraliaoccurredtensofmillenniabeforesimilareventsinNorthandSouthAmerica,Madagascar,andNewZealand,eachofwhichwasprecededbythearrivalofhumans).Apredictionoftheªblitzkriegºmodelofhuman-inducedextinction[asproposedfirstforNorthAmerica()andlaterforNewZealand()]isthatmegafaunalextinc-tionshouldoccursoonafterhumancoloniza-tion,andthatextinctionisfollowedbywide-spreadecosystemdisruption().Alternative-ly,humanarrivalmayfirsthavetriggeredecosystemdisruption,asaresultofwhichthemegafaunabecameextinct().Thelatterse-quenceofeventsallowsforasubstantialtimeintervalbetweenhumancolonizationandmegafaunalextinction,sothatclimaticfac-torsmayalsobeinvolved().Thereissufficientuncertaintyintheagesforbothhumancolonizationandmegafaunalextinc-tionthatwecannotdistinguishbetweenthesepossibilities,butourdataareconsistentwithahumanroleinextinction.Resolvingthisdebatewouldrequiremorepreciseagesforhumancolonizationandmegafaunalextinc-tion,aswellasanimprovedunderstandingofhumaninteractionswiththeAustralianland-scapeandbiotaduringtheearliestperiodofhumanoccupation.ReferencesandNotes1.T.F.Flannery,Archaeol.Oceania,45(1990).2.P.Murray,inVertebratePalaeontologyofAustralasiaP.Vickers-Rich,J.M.Monaghan,R.F.Baird,T.H.Rich,Eds.(PioneerDesignStudio,Melbourne,1991),pp.3.T.F.Flannery,R.G.Roberts,inExtinctionsinNearTime:Causes,Contexts,andConsequences,R.D.E.MacPhee,Ed.(KluwerAcademic/Plenum,NewYork,1999),pp.239Ð255.4.C.S.Wilkinson,Proc.Linn.Soc.NewSouthWales1207(1884).5.R.Owen,ResearchesontheFossilRemainsoftheExtinctMammalsofAustralia(Erxleben,London,6.D.Merrilees,J.R.Soc.West.Austr.,1(1968).7.R.Jones,Archaeol.Phys.Anthropol.Oceania,1868.G.H.Milleretal,205(1999).9.R.G.Roberts,R.Jones,M.A.Smith,,15310.R.G.RobertsetalQuat.Sci.Rev.,575(1994).AncientTL,19(1998).12.J.M.Bowler,D.M.Price,Archaeol.Oceania,15613.A.ThorneetalJ.Hum.Evol.,591(1999).14.D.R.Horton,inQuaternaryExtinctions:APrehistoricP.S.Martin,R.G.Klein,Eds.(Univ.ofArizonaPress,Tucson,AZ,1984),pp.639Ð680.15.A.Baynes,Rec.West.Austr.Mus.(suppl.57),39116.D.J.Meltzer,J.I.Mead,inEnvironmentsandExtinc-tions:ManinLateGlacialNorthAmerica,J.I.Mead,D.J.Meltzer,Eds.(CenterfortheStudyofEarlyMan,Univ.ofMaine,Orono,ME,1985),pp.145Ð173.17.J.P.White,T.F.Flannery,Austr.Archaeol.,1318.S.VanHuet,R.Gru¬n,C.V.Murray-Wallace,N.Red-vers-Newton,J.P.White,Austr.Archaeol.19.C.S.M.TurneyetalQuat.Res.,3(2001).20.Opticalageswerecalculatedfromtheburialdose(paleodose),measuredusingthephoton-stimulatedluminescence(PSL)signal,dividedbythedoserateduetoionizingradiation(21,22).TheportionofeachsampleexposedtodaylightwasÞrstremovedunderdimredilluminationanddiscarded.Quartzgrainsinthreerangesofdiameter(90to125m,180to212m,and125to250m)wereextractedfromtheremainingsampleusingstandardprocedures()andetchedin40%hydroßuoricacidfor45min.Asatestofinternalconsistency,somestratigraphicunitsweredatedusingmorethanonesampleorgrain-sizefraction.Paleodoseswereobtainedusingsingle-ali-quotregenerative-doseprotocols,statisticalmodels,andexperimentalapparatusasdescribed(Eachaliquotwasilluminatedfor100to125sat125¡C,andpaleodoseswerecalculatedfromtheÞrst3to5sofPSLarisingfromtheburial,regenerative,andtestdoses,usingtheÞnal20sasbackground.Eachsamplewasgivenapreheatplateautest(usingaliquotscomposedof100grains,andare-peatregenerativedosewasgiventoverifythattheprotocolyieldedthecorrect(known)dose(35,36ThepaleodosesinTable2wereobtainedfromali-quotstypicallycomposedof10grainstopermitdetectionofinsufÞcientbleachingbeforeburialfromexaminationofthepaleodosedistribution().Forsampleswithclearlyasymmetrical(positivelyskewed)distributions,meanpaleodoseswerecalcu-latedusingtheminimumagemodel();thecentralagemodel()wasusedforothersamples.Forsomesamples,paleodoseswerealsoobtainedusingthestandardmultiple-aliquotadditive-dosemethod(ThedoseratesduetoUandTh(andtheirdaughterproducts)andduetoKwerecalculatedfromacombinationofhigh-resolutiongammaandalphaspectrometry(tocheckfordisequilibriaintheUandThdecayseries),thick-sourcealphacounting,x-rayßuorescenceofpowderedsamples,andÞeldmeasurementsofthegammadoserate.Cosmic-raydoserateswereestimatedfrompub-lisheddata[J.R.Prescott,J.T.Hutton,Radiat.Meas.,497(1994)]andaneffectiveinternalalphadoserateof0.03Gykawasassumedforallsamples.Gammaandbetadoserateswerecorrectedfortheestimatedlong-termwatercontentofeachsampleandforbeta-doseattenuation[V.Mejdahl,,61(1979)].Weusedthesedimentfar-thestfromthebonetodatethemuseumspecimenstominimizeanydoserateheterogeneityinthesed-imentsadjacenttothebone.Thegammadoseratesforthemuseumspecimenswereestimatedfromtheattachedlumpsofsedimentandfromsedi-ment-bonemixtures,usinganuncertaintyof20%toaccommodateanyspatialinhomogeneityinthegammaradiationÞeld.ThisuncertaintywasalsoappliedtoÞeldsamplescollectedwithoutmeasuringtheinsitugammadoserate;insitumeasurementshaduncertaintiesoflessthanSomesampleshadasigniÞcantdeÞcitorexcessofUwithrespecttoRa(seeTable2).Theopticalagesforthesesampleswerecalculatedusingthemeasuredradionuclideconcentrations,butanyerrorduetopost-burialuraniummigrationshouldbeaccommodatedwithintheageuncer-21.D.J.Huntley,D.I.Godfrey-Smith,M.L.W.Thewalt,,105(1985).22.M.J.Aitken,AnIntroductiontoOpticalDating:TheDatingofQuaternarySedimentsbytheUseofPho-ton-StimulatedLuminescence(OxfordUniv.Press,Oxford,1998).23.J.Field,J.Dodson,Proc.Prehist.Soc.,275(1999).24.L.K.Ayliffeetal,147(1998).25.K.C.Moriarty,M.T.McCulloch,R.T.Wells,M.C.Palaeogeogr.Palaeoclimatol.Palaeoecol.,113(2000).26.AgescorrectedfordetritalThcontaminationwereobtainedbydeterminingthethoriumanduraniumisotopecompositionsfordifferentsplitsofthesameßowstone(eachsplitcontainingdifferentproportionsofthedetritalendmemberandthepureauthigeniccalcitephase).MixinglineplotsofThversusTh,andofThversusprovideestimatesofthedetritallycorrectedUandUratiosaswellastheisotoperatiosofthedetritalendmemberphases:(KudjalYolgahCave);0.02(MammothCave,upper0.03(MammothCave,lowerßow-stone);and0.01(MoondyneCave,usingtheaveragedetritalendmemberisotoperatiosfromÞvenearbysites).Thehalf-livesofUandThusedintheagecalculationare244,600490yearsand590years,respectively.27.SeethesupplementaryÞgureat28.G.J.Prideaux,G.A.Gully,L.K.Ayliffe,M.I.Bird,R.G.J.Vertebr.Paleontol.(suppl.tono.3),62A(2000).29.Single-grainopticaldatingandÞnitemixturemodels[R.G.Roberts,R.F.Galbraith,H.Yoshida,G.M.Laslett,J.M.Olley,Radiat.Meas.,459(2000)]wereusedtodistinguishpaleodose(andhenceage)populationsinthesedimentsamples.Multipledis-cretepopulationswereidentiÞed,whichweattributetothemixingofgrainswithdifferentburialhistories.Thepopulationswiththehighestpaleodoses(Table2)yieldedopticalagesconsistentwiththeCagesobtainedfrompiecesofcharcoal(30.WecannotbecertainthatarticulatedremainswererecoveredfromtheuppermegafaunalunitatMam-mothCave(site24),sotheopticalageof559kawasnotincludedinthedataset.31.P.S.Martin,D.W.Steadman,inExtinctionsinNearTime:Causes,Contexts,andConsequences,R.D.E.MacPhee,Ed.(KluwerAcademic/Plenum,NewYork,1999),pp.17Ð55.32.P.S.Martin,,969(1973).33.R.N.Holdaway,C.Jacomb,,225034.Muchofthe60-to40-kaintervalwasmarkedbygenerallywetterconditionsthanatpresentinbotheasternAustralia(24,38)[G.C.Nanson,D.M.Price,S.A.Short,,791(1992);J.M.Bowler,Archaeol.Oceania,120(1998)]andsouthwesternAustralia[J.Balme,D.Merrilees,J.K.Porter,J.R.Soc.West.Austr.,33(1978),usingtherevisedchro-nologyforDevilÕsLair()].Butmonsoonalactivitymayhavebeenvariablewithshort-livedclimaticoscillations(),inkeepingwithevidencefromdeep-seacoresofclimateinstability[J.P.Sachs,S.J.,756(1999);S.L.Kanfoush,1815(2000)].35.R.F.Galbraith,R.G.Roberts,G.M.Laslett,H.Yoshida,J.M.Olley,,339(1999).36.H.Yoshida,R.G.Roberts,J.M.Olley,G.M.Laslett,R.F.Galbraith,Radiat.Meas.,439(2000).37.J.M.Olley,G.G.Caitcheon,R.G.Roberts,,207(1999).38.B.J.Johnsonetal,1150(1999).39.WethankS.Eberhard,J.Field,G.Gully,L.Hatcher,R.McBeath,D.Merrilees,G.Miller,R.Molnar,K.Mori-arty,A.Ritchie,I.Sobbe,thelateG.vanTets,J.Wilkinson,D.Witter,T.Worthy,andR.Wrightforsamplecollection,Þeldassistance,anddiscussions;theWesternAustralianMuseumandMuseumofVictoriaforpermissiontoaccesstheircollections;M.Olleyforpreparingthegammaspectrometrysam-ples;R.Galbraithformixturemodeling;andR.GillespieandO.Lianforcomments.SupportedbyaLargeGrantandaQueenElizabethIIFellowshipfromtheAustralianResearchCouncil(R.G.R.).27February2001;accepted25April20018JUNE2001VOL292SCIENCEwww.sciencemag.org