Humanity’simpactontheEarthisnowsoprofoundthatanewgeologicalepoch–theAnthropocene–needsto bedeclared,accordingto anofficialexpertgroupwhopresentedtherecommendationtotheInternationalGeologicalCongressinCapeTownonMonday.

Thenewepochshouldbeginabout1950,theexpertssaid,andwaslikelyto bedefinedbytheradioactiveelementsdispersedacrosstheplanetbynuclearbombtests,althoughanarrayofothersignals,includingplasticpollution,sootfrompowerstations,concrete,andeventhebonesleftbytheglobalproliferationofthedomesticchickenwerenowunderconsideration.

Thecurrentepoch,theHolocene,isthe12,000yearsofstableclimatesincethelasticeageduringwhichallhumancivilisationdeveloped.Butthestrikingaccelerationsincethemid-20thcenturyofcarbondioxideemissionsandsealevelrise,theglobalmassextinctionofspecies,andthetransformationoflandbydeforestationanddevelopmentmarktheendofthatsliceofgeologicaltime,theexpertsargue.TheEarthis soprofoundlychangedthattheHolocenemustgivewaytotheAnthropocene.

“ThesignificanceoftheAnthropoceneisthatitsetsadifferenttrajectoryfortheEarthsystem,ofwhichwe ofcoursearepart,”saidProfJanZalasiewicz,ageologistattheUniversityofLeicesterandchairoftheWorkingGroupontheAnthropocene(WGA),whichstartedworkin 2009.

“Ifourrecommendationisaccepted,theAnthropocenewillhavestartedjustalittlebeforeIwasborn,”hesaid.“WehavelivedmostofourlivesinsomethingcalledtheAnthropoceneandarejustrealisingthescaleandpermanenceofthechange.”

ProfColinWaters,principalgeologistattheBritishGeologicalSurveyandWGAsecretary,said:“Beingabletopinpointanintervaloftimeissayingsomethingabouthowwehavehadanincredibleimpactontheenvironmentofourplanet.TheconceptoftheAnthropocenemanagestopullalltheseideasofenvironmentalchangetogether.”

ProfChrisRapley,aclimatescientistatUniversityCollegeLondonandformerdirectoroftheScienceMuseuminLondonsaid:“TheAnthropocenemarksanewperiodinwhichourcollectiveactivitiesdominatetheplanetarymachinery.

“Sincetheplanetisourlifesupportsystem– weareessentiallythecrewof alargishspaceship–interferencewithitsfunctioningatthislevelandonthisscaleishighlysignificant.Ifyouor Iwerecrewon asmallerspacecraft,itwouldbeunthinkabletointerferewiththesystemsthatprovideuswithair,water,fodderandclimatecontrol.ButtheshiftintotheAnthropocenetellsusthatweareplayingwithfire,apotentiallyrecklessmodeofbehaviourwhichwearelikelytocometoregretunlesswegetagriponthesituation.”RapleyisnotpartoftheWGA.

MartinRees,theastronomerroyalandformerpresidentoftheRoyalSociety,saidthatthedawnoftheAnthropocenewasasignificantmoment.“Thedarkestprognosisforthenextmillenniumisthatbio,cyberorenvironmentalcatastrophescouldforeclosehumanity’simmensepotential,leavingadepletedbiosphere,”hesaid.

ButLordReesaddedthatthereisalsocauseforoptimism.“Humansocietiescouldnavigatethesethreats,achieveasustainablefuture,andinaugurateerasofpost-humanevolutionevenmoremarvellousthanwhat’sledtous.ThedawnoftheAnthropoceneepochwouldthenmarkaone-offtransformationfromanaturalworldtoonewherehumansjumpstartthetransitiontoelectronic(andpotentiallyimmortal)entities,thattranscendourlimitationsandeventuallyspreadtheirinfluencefarbeyondtheEarth.”

Theevidenceofhumanity’simpactontheplanetisoverwhelming,butthechangesareveryrecentingeologicalterms,whereanepochusuallyspanstensofmillionsofyears.“OnecriticismoftheAnthropoceneasgeologyisthatit isveryshort,”saidZalasiewicz.“Ourresponseisthatmanyofthechangesareirreversible.”

Todefineanewgeologicalepoch,asignalmustbefoundthatoccursgloballyandwillbeincorporatedintodepositsinthefuturegeologicalrecord.Forexample,theextinctionofthedinosaurs66myearsagoattheendoftheCretaceousepochisdefinedby a “goldenspike”insedimentsaroundtheworldofthemetaliridium,whichwasdispersedfromthemeteoritethatcollidedwithEarthtoendthedinosaurage.

FortheAnthropocene,thebestcandidateforsuchagoldenspikeareradioactiveelementsfromnuclearbombtests,whichwereblownintothestratospherebeforesettlingdowntoEarth.“Theradionuclidesareprobablythesharpest–theyreallycomeonwithabang,”saidZalasiewicz.“But wearespoiledforchoice.Therearesomanysignals.”

OtherspikesbeingconsideredasevidenceoftheonsetoftheAnthropoceneincludethetough,unburnedcarbonspheresemittedbypowerstations.“TheEarthhasbeensmoked,withsignalsveryclearlyaroundtheworldinthemid-20thcentury,”saidZalasiewicz.

Othercandidatesincludeplasticpollution,aluminiumandconcreteparticles,andhighlevelsofnitrogenandphosphateinsoils,derivedfromartificialfertilisers.Althoughtheworldiscurrentlyseeingonlythesixthmassextinctionofspeciesinthe700m-yearhistoryofcomplexlifeonEarth,thisisunlikelytoprovideausefulgoldenspikeastheanimalsarebydefinitionveryrareandrarelydispersedworldwide.

Incontrast,somespecieshavewithhumanhelpspreadrapidlyacrosstheworld.Thedomesticchickenis aseriouscontenderto be afossilthatdefinestheAnthropoceneforfuturegeologists.“Sincethemid-20thcentury,ithasbecometheworld’smostcommonbird.Ithasbeenfossilisedinthousandsoflandfillsitesandonstreetcornersaroundtheworld,”saidZalasiewicz.“It is isalsoamuchbiggerbirdwithadifferentskeletonthanitsprewarancestor.”

The35scientistsontheWGA–whovoted30 tothreeinfavourofformallydesignatingtheAnthropocene,withtwoabstentions–willnowspendthenexttwotothreeyearsdeterminingwhichsignalsarethestrongestandsharpest.Crucially,theymustalsodecidealocationwhichwilldefinethestartoftheAnthropocene.Geologicaldivisionsarenotdefinedbydatesbutby aspecificboundarybetweenlayersofrockor,inthecaseoftheHolocene,aboundarybetweentwoicelayersin acoretakenfromGreenlandandnowstoredinDenmark.

ThescientistsarefocusingonsiteswhereannuallayersareformedandareinvestigatingmudsedimentsoffthecoastofSantaBarbarainCaliforniaandtheErnestocaveinnorthernItaly,wherestalactitesandstalagmitesaccreteannualrings.Lakesediments,icecoresfromAntarctica,corals,treeringsandevenlayersofrubbishinlandfillsitesarealsobeingconsidered.

Oncethedatahasbeenassembled,itwillbeformallysubmittedtothestratigraphicauthoritiesandtheAnthropocenecouldbeofficiallyadoptedwithinafewyears.“If wewereveryluckyandsomeonecameforwardwith,say,acorefromaclassicexampleoflaminatedsedimentsin adeepmarineenvironment,Ithinkthreeyearsispossiblyviable,”saidZalasiewicz.

Thiswouldbelightningspeedforsuchageologicaldecision,whichinthepastwouldhavetakendecadesandevencenturiestomake.ThetermAnthropocenewascoinedonlyin 2000, bytheNobelprize-winningscientistPaulCrutzen,whobelievesthenamechangeisoverdue.Hesaidin 2011: “Thisnamechangestressestheenormityofhumanity’sresponsibilityasstewardsoftheEarth.”Crutzenalsoidentifiedin 2007whathecalledthe“greatacceleration”ofhumanimpactsontheplanetfromthemid-20thcentury.

DespitetheWGA’sexpertrecommendation,thedeclarationoftheAnthropoceneisnotyetaforegoneconclusion.“Ourstratigraphiccolleaguesareveryprotectiveofthegeologicaltimescale.Theyseeitveryrightlyasthebackboneofgeologyandtheydonotamenditlightly,”saidZalasiewicz.“But Ithinkwecanprepareaprettygoodcase.”

Rapleyalsosaidtherewasastrongcase:“It ishighlyappropriatethatgeologistsshouldpayformalattentionto achangeinthesignalwithinsedimentaryrocklayersthatwillbeclearlyapparenttofuturegenerationsofgeologistsforaslongastheyexist.The‘greatacceleration’constitutesastrong,detectableandincontrovertiblesignal.”

Evidence of the Anthropocene

Humanactivityhas:

•Pushedextinctionratesofanimalsandplantsfarabovethelong-termaverage.TheEarthis oncoursetosee75% ofspeciesbecomeextinctinthenextfewcenturiesifcurrenttrendscontinue.

•Increasedlevelsofclimate-warmingCO2intheatmosphereatthefastestratefor66myears,withfossil-fuelburningpushinglevelsfrom280partspermillionbeforetheindustrialrevolutionto 400ppmandrisingtoday.

•Putsomuchplasticinourwaterwaysandoceansthatmicroplasticparticlesarenowvirtuallyubiquitous,andplasticswilllikelyleaveidentifiablefossilrecordsforfuturegenerationstodiscover.

•Doubledthenitrogenandphosphorousinoursoilsinthepastcenturywithfertiliseruse.Thisislikelyto bethelargestimpactonthenitrogencyclein 2.5bnyears.

•Leftapermanentlayerofairborneparticulatesinsedimentandglacialicesuchasblackcarbonfromfossilfuelburning.