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时间:2021-09-30
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1、UnderstandingEarthChapter8:TheRockRecordandtheGeologicTimeScaleCopyright©2007byW.H.Freeman&CompanyJohnGrotzinger,ThomasH.JordanFrankPressandRaymondSieverFifthEditionConceptsyouwillneedtoknowfortheexamsCHAPTER8GeologicTimeScaleRelativeageAbsoluteagePrincipleoforiginalhorizontalityPrincipleofsuper
2、positionPrincipleofcross-cuttingrelationahipsUnconformityAngularunconformityDisconformityHalf-lifeGeologicTimeScaleGeologistsdifferfromotherprofessionalscientistsintheirviewoftime.Geologistsdealwithperiodsoftimethatgoasfarbackastheoriginoftheuniverse.Beforewehadtheabilitytoreadthe“atomicclocks”o
3、fnature,geologistsusedtheconceptofrelativeages.Wecanseechangesinthelandscapeovertime.Wecanseeonetypeoforganismreplaceanothertypeoforganismthroughthefossilizedremainsofthesechangesovertime.Withtheadventofatomic/radioactivedecaytechniqueswebegantoobtainabsolutedates.Absolutedatesorageshavespecific
4、numbersRelativedatinghasbeendoneinthepastthroughthestudyoflayersofsedimentaryrock(aka“thefieldofstratigraphy”)PrincipleofOriginalHorizontalitysedimentsdepositedinnearlyflatlayers.Cross-beddedlayersarecontainedwithinoverallflatbeds.Iflayersarefaulted(broken)orfoldeditmeansthattheyweredeformedAFTE
5、Rsedimentsweredeposited.PrincipleofSuperpositionLowestlayersareolderIfthisisnotso,thenthelayershavebeenoverturnedbytectonicactivity:Therearelimitationsforusingstratigraphytokeeptimebecause,(1)sedimentationratesarevariablee.g.Mississippicandeposit1mofsedimentin1000yThedeepoceanmaydeposit1mm/1000y
6、earsWeneedtoestimatetimeinanotherwayandbeabletorecognizewhentherepresentationoftimeviasedimentsisincomplete.Paleontologyisthestudyofancientlifefromfossilizedremains.WilliamSmithinthe19thcenturywasanengineerwhonotedthatsimilarrocksindifferentareashadsimilarfossilsandthatdifferentrocktypeshaddiffe
7、rentfossils.Hemadeacomposite(ideal,pieced-together)stratigraphicsuccessionasinthefollowingfigureMostofgeologictimegoesunrecordedSometimesNOSEDIMENTisDEPOSITEDoveranintervaloftime(hiatus)Othertimessedimentiserodedaway.Thisish
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