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Our Ever Changing Earh.pdf

Our Ever Changing Earh

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2009-10-22 0人阅读 举报 0 0 0 暂无简介

简介:本文档为《Our Ever Changing Earhpdf》,可适用于其他资料领域

WWWSCIAMCOMMovingMountainsPoweroftheGeodynamoNomadicContinentsSurfaceSculptingfromWithinSecretEarthquakesRevealed:SeafloorVistasOurEverChangingEARTHCOPYRIGHTSCIENTIFICAMERICAN,INCEDITORINCHIEF:JohnRennieEXECUTIVEEDITOR:MarietteDiChristinaISSUEEDITOR:LarryKatzensteinARTDIRECTOR:EdwardBellISSUEDESIGNER:LucyReadingIkkandaPHOTOGRAPHYEDITORS:EmilyHarrison,SmithaAlampurPRODUCTIONEDITOR:JosephManghiseCOPYDIRECTOR:MariaChristinaKellerCOPYCHIEF:MollyKFrancesASSISTANTCOPYCHIEF:DanielCSchlenoffCOPYANDRESEARCH:MichaelBattaglia,SaraBeardsley,KennethSilberEDITORIALADMINISTRATOR:JacobLaskySENIORSECRETARY:MayaHartyASSOCIATEPUBLISHER,PRODUCTION:WilliamShermanMANUFACTURINGMANAGER:JanetCermakADVERTISINGPRODUCTIONMANAGER:CarlCherebinPREPRESSANDQUALITYMANAGER:SilviaDeSantisPRODUCTIONMANAGER:ChristinaHippeliCUSTOMPUBLISHINGMANAGER:MadelynKeyesMilchASSOCIATEPUBLISHERVICEPRESIDENT,CIRCULATION:LorraineLeibTerleckiRENEWALSMANAGER:KarenSingerASSISTANTCIRCULATIONBUSINESSMANAGER:JonathanPrebichFULFILLMENTANDDISTRIBUTIONMANAGER:RosaDavisVICEPRESIDENTANDPUBLISHER:BruceBrandfonDIRECTOR,CATEGORYDEVELOPMENT:JimSilvermanWESTERNSALESMANAGER:DebraSilverSALESDEVELOPMENTMANAGER:DavidTirpackWESTERNSALESDEVELOPMENTMANAGER:ValerieBantnerSALESREPRESENTATIVES:StephenDudley,HunterMillington,StanSchmidtASSOCIATEPUBLISHER,STRATEGICPLANNING:LauraSalantPROMOTIONMANAGER:DianeSchubeRESEARCHMANAGER:AidaDadurianPROMOTIONDESIGNMANAGER:NancyMongelliGENERALMANAGER:MichaelFlorekBUSINESSMANAGER:MarieMaherMANAGER,ADVERTISINGACCOUNTINGANDCOORDINATION:ConstanceHolmesDIRECTOR,SPECIALPROJECTS:BarthDavidSchwartzMANAGINGDIRECTOR,ONLINE:MinaCLuxOPERATIONSMANAGER,ONLINE:VincentMaSALESREPRESENTATIVE,ONLINE:GaryBronsonMARKETINGDIRECTOR,ONLINE:HanKoDIRECTOR,ANCILLARYPRODUCTS:DianeMcGarveyPERMISSIONSMANAGER:LindaHertzMANAGEROFCUSTOMPUBLISHING:JeremyAAbbateCHAIRMANEMERITUS:JohnJHanleyCHAIRMAN:JohnSargentPRESIDENTANDCHIEFEXECUTIVEOFFICER:GretchenGTeichgraeberVICEPRESIDENTANDMANAGINGDIRECTOR,INTERNATIONAL:DeanSandersonVICEPRESIDENT:FrancesNewburgOurEverChangingEarthispublishedbythestaffofScientificAmerican,withprojectmanagementby:wwwsciamcomSCIENTIFICAMERICANEstablished®it’ssoboring,theusualhuman’seyeviewSeasonscomeandgo,butterrafirmaitselfnevervariesEvenanearthquakeoramudslideseemslikearandomincidentunconnectedtoanylargerormorecomplexpatternsButputonthelensesofageologistandtakeanotherlookReadingthestoriesimprintedontherocksandcrystalsgivesscientiststheabilitytoexamineourworldasithasevolvedovermillions,evenbillions,ofyearsFromthisvantagepoint,itiseasytoseethatEarthhasbeenandcontinuestobealivelycauldronofchangeJustasstopactionphotographyshowshowbudsburstintoflower,geologygivesusapictureofaliving,changingplanetItevenhasaheartbeatofsorts,inpulsedreleasesofvastamountsofinnerheatThemostrecentoccurredwhendinosaursstillroamed,asRogerLLarsondiscussesin“TheMidCretaceousSuperplumeEpisode,”onpageAsscientistsdrawonrecordsofpasttremors,itbecomesclearthatearthquakes,whichseemedtobeisolated,caninteractwithoneanotherIn“EarthquakeConversations,”onpage,RossSSteinexplainshowthesesurprisinginterconnectedeffectscouldgivenations,citiesandindividualsnewpowertoevaluatelocalvulnerabilitytotemblorsInanotherplacewheretakingthelongviewaltersoureverydaynotions,welearnthaterosionlongfamiliarasthegreatlevelerhasalsohadahandinshapingthetallestpeaks,theHimalayasErodingland,byreducingweight,acceleratestectonicprocesses,creatinganupliftTurntopagefor“HowErosionBuildsMountains,”byNicholasPinterandMarkTBrandonDeepunderthemorphingsurface,theinteriorsimmersThechurningmantlecreatesandpowerstheprimarymagneticfieldthatsurroundsthesphereThepolarityofthisfieldreverseseverysooften,whichhaslongpuzzledresearchers“ProbingtheGeodynamo,”byGaryAGlatzmaierandPeterOlson,onpage,tellsofnew,intriguingcluesabouthowthenextreversalmaybeginSojoinusforajauntingeology’srockencrustedtimemachineThearticlesinthisspecialeditionpromiseararelookinsidethemysteriousandlittleappreciatedunderfootactivitiesoftheworldweallcallhomeKENNBROWNletterfromtheeditorADeeperUnderstandingMarietteDiChristinaExecutiveEditorScientificAmericaneditorssciamcomCOPYRIGHTSCIENTIFICAMERICAN,INCCREDITTheCoreMantleBoundaryByRaymondJeanlozandThorneLayThisinteractivezonemaybethemostdynamicpartoftheplanet,directlyaffectingEarth’srotationandmagneticfieldTheEvolutionofContinentalCrustBySRossTaylorandScottMMcLennanThehighstandingcontinentsowetheirexistencetoEarth’slonghistoryofplatetectonicactivityPanoramasoftheSeafloorByLincolnFPratsonandWilliamFHaxbyModernsonartechniquesmapthecontinentalmarginsoftheUSandrevealtherichlyvariedsceneryusuallyhiddenunderwaterContentsOurEverChangingEarthSCIENTIFICAMERICANSCIENTIFICAMERICANLetterfromtheEditorINTHEBEGINNINGTheEvolutionofEarthByClaudeJAllègreandStephenHSchneiderTheevolutionofthisplanetanditsatmospheregaverisetolife,whichshapedEarth’ssubsequentdevelopmentOurfutureliesininterpretingthisgeologicpastandconsideringwhatchangesgoodandbadmaylieaheadEarthbeforePangaeaByIanWDDalzielTheNorthAmericancontinentmaybemorenomadicthanmostofitsinhabitantsTheMidCretaceousSuperplumeEpisodeByRogerLLarsonEarthhasanerratic“heartbeat”thatcanreleasevastamountsofheatfromdeepwithintheplanetThelatest“pulse”occurredmillionyearsagoSEARCHINGBELOWTHESURFACEProbingtheGeodynamoByGaryAGlatzmaierandPeterOlsonScientistshavewonderedwhythepolarityofEarth’smagneticfieldoccasionallyreversesRecentstudiesofferintriguingcluesabouthowthenextreversalmaybeginVolume,NumberTheCoreMantleBoundaryByRaymondJeanlozandThorneLayThisinteractivezonemaybethemostdynamicpartoftheplanet,directlyaffectingEarth’srotationandmagneticfieldTheEvolutionofContinentalCrustBySRossTaylorandScottMMcLennanThehighstandingcontinentsowetheirexistencetoEarth’slonghistoryofplatetectonicactivityPanoramasoftheSeafloorByLincolnFPratsonandWilliamFHaxbyModernsonartechniquesmapthecontinentalmarginsoftheUSandrevealtherichlyvariedsceneryusuallyhiddenunderwaterContentsOurEverChangingEarthSCIENTIFICAMERICANSCIENTIFICAMERICANLetterfromtheEditorINTHEBEGINNINGTheEvolutionofEarthByClaudeJAllègreandStephenHSchneiderTheevolutionofthisplanetanditsatmospheregaverisetolife,whichshapedEarth’ssubsequentdevelopmentOurfutureliesininterpretingthisgeologicpastandconsideringwhatchangesgoodandbadmaylieaheadEarthbeforePangaeaByIanWDDalzielTheNorthAmericancontinentmaybemorenomadicthanmostofitsinhabitantsTheMidCretaceousSuperplumeEpisodeByRogerLLarsonEarthhasanerratic“heartbeat”thatcanreleasevastamountsofheatfromdeepwithintheplanetThelatest“pulse”occurredmillionyearsagoSEARCHINGBELOWTHESURFACEProbingtheGeodynamoByGaryAGlatzmaierandPeterOlsonScientistshavewonderedwhythepolarityofEarth’smagneticfieldoccasionallyreversesRecentstudiesofferintriguingcluesabouthowthenextreversalmaybeginVolume,NumberCOPYRIGHTSCIENTIFICAMERICAN,INCCREDITFORCESTHATSHAPEANDSHAKEEARTHSculptingEarthfromInsideOutByMichaelGurnisPowerfulmotionsdeepinsidetheplanetdonotmerelyshovefragmentsoftherockyshellhorizontallyaroundtheglobetheyalsoliftandlowerentirecontinentsEarth’sMantlebelowtheOceansByEnricoBonattiSamplescollectedfromtheoceanfloorrevealhowthemantle’sconvectiveforcesshapeEarth’ssurface,createitscrustandperhapsevenaffectitsrotationHowErosionBuildsMountainsByNicholasPinterandMarkTBrandonAnunderstandingofhowtectonic,erosionalandclimaticforcesinteracttoshapemountainspermitsclearerinsightsintoEarth’shistoryEarthquakeConversationsByRossSSteinContrarytoprevailingwisdom,largeearthquakescaninteractinunexpectedwaysThisexcitingdiscoverycoulddramaticallyimprovescientists’abilitytopinpointfutureshocksTheThreatofSilentEarthquakesByPeterCervelliAlackofrumblingdoesnotnecessarilymakeanearthquakeharmlessSomeofthequiettypescouldpresagedevastatingtsunamisorlarger,groundshakingshocksCoverillustrationbyKennBrownScientificAmericanSpecial(ISSN),Volume,Number,,publishedbyScientificAmerican,Inc,MadisonAvenue,NewYork,NYCopyright©byScientificAmerican,IncAllrightsreservedNopartofthisissuemaybereproducedbyanymechanical,photographicorelectronicprocess,orintheformofaphonographicrecording,normayitbestoredinaretrievalsystem,transmittedorotherwisecopiedforpublicorprivateusewithoutwrittenpermissionofthepublisherCanadianBNNoRTQSTNoQTopurchaseadditionalquantities:US,$eachelsewhere,$eachSendpaymenttoScientificAmerican,DeptES,MadisonAvenue,NewYork,NYInquiries:faxortelephonePrintedinUSAFORCESTHATSHAPEANDSHAKEEARTHSculptingEarthfromInsideOutByMichaelGurnisPowerfulmotionsdeepinsidetheplanetdonotmerelyshovefragmentsoftherockyshellhorizontallyaroundtheglobetheyalsoliftandlowerentirecontinentsEarth’sMantlebelowtheOceansByEnricoBonattiSamplescollectedfromtheoceanfloorrevealhowthemantle’sconvectiveforcesshapeEarth’ssurface,createitscrustandperhapsevenaffectitsrotationHowErosionBuildsMountainsByNicholasPinterandMarkTBrandonAnunderstandingofhowtectonic,erosionalandclimaticforcesinteracttoshapemountainspermitsclearerinsightsintoEarth’shistoryEarthquakeConversationsByRossSSteinContrarytoprevailingwisdom,largeearthquakescaninteractinunexpectedwaysThisexcitingdiscoverycoulddramaticallyimprovescientists’abilitytopinpointfutureshocksTheThreatofSilentEarthquakesByPeterCervelliAlackofrumblingdoesnotnecessarilymakeanearthquakeharmlessSomeofthequiettypescouldpresagedevastatingtsunamisorlarger,groundshakingshocksBONUSARTICLENewLightonDeepEarthquakesByHarryWGreenIIUntilaboutyearsago,itwasamysteryhowlongdeepearthquakescouldoccurRecentrestulthavenowdemonstratedmechanismsforsuchrockfailuresatgreatdepthsCoverillustrationbyKennBrownScientificAmericanSpecial(ISSN),Volume,Number,,publishedbyScientificAmerican,Inc,MadisonAvenue,NewYork,NYCopyright©byScientificAmerican,IncAllrightsreservedNopartofthisissuemaybereproducedbyanymechanical,photographicorelectronicprocess,orintheformofaphonographicrecording,normayitbestoredinaretrievalsystem,transmittedorotherwisecopiedforpublicorprivateusewithoutwrittenpermissionofthepublisherCanadianBNNoRTQSTNoQTopurchaseadditionalquantities:US,$eachelsewhere,$eachSendpaymenttoScientificAmerican,DeptES,MadisonAvenue,NewYork,NYInquiries:faxortelephonePrintedinUSACOPYRIGHTSCIENTIFICAMERICAN,INCCREDITEvolutionEarthTheofTheevolutionofthisplanetanditsatmospheregaverisetolife,whichshapedEarth’ssubsequentdevelopmentOurfutureliesininterpretingthisgeologicpastandconsideringwhatchangesgoodandbadmaylieaheadByClaudeJAllègreandStephenHSchneiderSCIENTIFICAMERICANOUREVERCHANGINGEARTHCOPYRIGHTSCIENTIFICAMERICAN,INCCREDITEARTHSEENFROMSPACEhaschangeddramaticallyOnehundredmillionyearsafterithadformedsomefourbillionyearsagotheplanetwasprobablyundergoingmeteorbombardment(left)Atthistime,itmayhavebeenstuddedwithvolcanicislandsandshroudedbyanatmosphereladenwithcarbondioxideandheavywithcloudsThreebillionyearsagoitsfacemayhavebeenobscuredbyanorangehazeofmethane,theproductofearlyorganisms(center)Todayclouds,oceansandcontinentsareclearlydiscernible(right)ThisillustrationwaspreparedwiththehelpofJamesFKastingofPennsylvaniaStateUniversityCOPYRIGHTSCIENTIFICAMERICAN,INCContinentsandoceans,encircledbyanoxygenrichatmosphere,supportfamiliarlifeformsYetthisconstancyisanillusionproducedbythehumanexperienceoftimeEarthanditsatmospherearecontinuouslyalteredPlatetectonicsshiftthecontinents,raisemountainsandmovetheoceanfloorwhileprocessesnotfullyunderstoodaltertheclimateSuchconstantchangehascharacterizedEarthsinceitsbeginningsomebillionyearsagoFromtheoutset,heatandgravityshapedtheevolutionoftheplanetTheseforcesweregraduallyjoinedbytheglobaleffectsoftheemergenceoflifeExploringthispastoffersustheonlypossibilityofunderstandingtheoriginoflifeand,perhaps,itsfutureScientistsusedtobelievetherockyplanets,includingEarth,Mercury,VenusandMars,werecreatedbytherapidgravitationalcollapseofadustcloud,adeflationgivingrisetoadenseorbInthestheApollospaceprogramchangedthisviewStudiesofmooncratersrevealedthatthesegougeswerecausedbytheimpactofobjectsthatwereingreatabundanceaboutbillionyearsagoThereafter,thenumberofimpactsappearedtohavequicklydecreasedThisobservationrejuvenatedthetheoryofaccretionpostulatedbyOttoSchmidtTheRussiangeophysicisthadsuggestedinthatplanetsgrewinsizegradually,stepbystepAccordingtoSchmidt,cosmicdustlumpedtogethertoformparticulates,particulatesbecamegravel,gravelbecamesmallballs,thenbigballs,thentinyplanets,orplanetesimals,and,finally,dustbecamethesizeofthemoonAstheplanetesimalsbecamelarger,theirnumbersdecreasedConsequently,thenumberofcollisionsbetweenplanetesimals,ormeteorites,decreasedFeweritemsavailableforaccretionmeantthatittookalongtimetobuildupalargeplanetAcalculationmadebyGeorgeWWetherilloftheCarnegieInstitutionofWashingtonsuggeststhataboutmillionyearscouldpassbetweentheformationofanobjectmeasuringkilometersindiameterandanobjectthesizeofEarthTheprocessofaccretionhadsignificantthermalconsequencesforEarth,consequencesthatforcefullydirecteditsevolutionLargebodiesslammingintotheplanetproducedimmenseheatinitsinterior,meltingthecosmicdustfoundthereTheresultingfurnacesituatedsometokilometersundergroundandcalledamagmaoceanwasactiveformillionsofyears,givingrisetovolcaniceruptionsWhenEarthwasyoung,heatatthesurfacecausedbyvolcanismandlavaflowsfromtheinteriorwasintensifiedbytheconstantbombardmentofhugeobjects,someofthemperhapsthesizeofthemoonorevenMarsNolifewaspossibleduringthisperiodBeyondclarifyingthatEarthhadformedthroughaccretion,theApolloprogramcompelledscientiststotrytoreconstructthesubsequenttemporalandphysicaldevelopmentoftheearlyEarthThisundertakinghadbeenconsideredimpossiblebyfoundersofgeology,includingCharlesLyell,towhomthefollowingphraseisattributed:Novestigeofabeginning,noprospectforanendThisstatementconveystheideathattheyoungEarthcouldnotberecreated,becauseitsremnantsweredestroyedbyitsveryactivityButthedevelopmentofisotopegeologyintheshadrenderedthisviewobsoleteTheirimaginationsfiredbyApolloandthemoonfindings,geochemistsbegantoapplythistechniquetounderstandtheevolutionofEarthDatingrocksusingsocalledradioactiveclocksallowsgeologiststoworkonoldterrainsthatdonotcontainfossilsThehandsofaradioactiveclockareisotopesatomsofthesameelementthathavedifferentatomicweightsandgeologictimeismeasuredbytherateofdecayofoneisotopeintoanothersee“TheEarliestHistoryoftheEarth,”byDerekYorkScientificAmerican,JanuaryAmongthemanyclocks,thosebasedonthedecayofuraniumintoleadandofuraniumintoleadarespecialGeochronologistscandeterminetheageofsamplesbyanalyzingonlythedaughterproductinthiscase,leadoftheradioactiveparent,uraniumPANNINGFORZIRCONSisotopegeologyhaspermittedgeologiststodeterminethattheaccretionofEarthculminatedinthedifferentiationoftheplanet:thecreationofthecorethesourceofEarth’smagneticfieldandthebeginningoftheatmosphereIntheclassicworkofClaireCPattersonoftheCaliforniaInstituteofTechnologyusedtheuraniumleadclocktoestabli

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