Geologic time scale

《Geologic time scale》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、GeologictimescaleFromWikipedia,thefreeencyclopediaThisclockrepresentationshowssomeofthemajorunitsofgeologicaltimeanddefinitiveeventsofEarthhistory.TheHadeaneonrepresentsthetimebeforefossilrecordoflifeonEarth;itsupperboundaryisnowregardedas4.0Ga(billionyearsago).[1]Othersubdivis

2、ionsreflecttheevolutionoflife;theArcheanandProterozoicarebotheons,thePalaeozoic,MesozoicandCenozoicareerasofthePhanerozoiceon.ThetwomillionyearQuaternaryperiod,thetimeofrecognizablehumans,istoosmalltobevisibleatthisscale.Thegeologictimescale(GTS)isasystemofchronologicalmeasurem

3、entthatrelatesstratigraphytotime,andisusedbygeologists,paleontologists,andotherEarthscientiststodescribethetimingandrelationshipsbetweeneventsthathaveoccurredthroughoutEarth’shistory.Thetableofgeologictimespanspresentedhereagreeswiththenomenclature,datesandstandardcolorcodesset

4、forthbytheInternationalCommissiononStratigraphy.EvidencefromradiometricdatingindicatesthatEarthisabout4.54billionyearsold.ThegeologyordeeptimeofEarth’spasthasbeenorganizedintovariousunitsaccordingtoeventswhichtookplaceineachperiod.DifferentspansoftimeontheGTSareusuallydelimited

5、bychangesinthecompositionofstratawhichcorrespondtothem,indicatingmajorgeologicalorpaleontologicalevents,suchasmassextinctions.Forexample,theboundarybetweentheCretaceousperiodandthePaleogeneperiodisdefinedbytheCretaceous–Paleogeneextinctionevent,whichmarkedthedemiseofthenon-avia

6、ndinosaursandmanyothergroupsoflife.Oldertimespanswhichpredatethereliablefossilrecord(beforetheProterozoicEon)aredefinedbytheabsoluteage.Contents[hide]1Terminology2Historyandnomenclatureofthetimescale3Condensedgraphicaltimelines4Tableofgeologictimeo4.1ProposedPrecambriantime

7、line5Seealso6Notesandreferences7Furtherreading8ExternallinksTerminology[edit]ehUnitsingeochronologyandstratigraphy[2]Segmentsofrock(strata)TimespansNotestoinchronostratigraphyingeochronologygeochronologicalunits4total,halfabillionEonothemEonyearsormore14total,severalhundred

8、ErathemEramillionyearsSystemPeriodSeriesEpochtensofmil