theEocene/ˈiːəsiːn/(symbolEo [2]) epoch, lasting from56to33.9million years ago, is a major division of thegeologic timescaleand the second epoch of thePaleogenePeriod in theCenozoicEra. The Eocene spans the time from the end of thePalaeoceneEpoch to the beginning of theOligoceneEpoch. The start of the Eocene is marked by a brief period in which the concentration of thecarbonisotope13Cin the atmosphere was exceptionally low in comparison with the more common isotope12C. The end is set at a majorextinction eventcalled theGrande Coupure(the "Great Break" in continuity) or theEoceneOligocene extinction event, which may be related to the impact of one or more largebolidesinSiberiaand in what is nowChesapeake Bay. As with othergeologic periods, thestratathat define the start and end of the epoch are well identified,[3]though their exact dates are slightly uncertain.
The nameEocenecomes from theGreekἠώς(eos,dawn) andκαινός(kainos, new) and refers to the "dawn" of modern ('new')faunathat appeared during the epoch.[4]
SystemSeriesStageAge(Ma)NeogeneMioceneAquitanianyoungerPaleogeneOligoceneChattian23.0328.1Rupelian28.133.9
EocenePriabonian33.938.0Bartonian38.041.3Lutetian41.347.8Ypresian47.856.0PaleoceneThanetian56.059.2Selandian59.261.6Danian61.666.0CretaceousLateMaastrichtianolderSubdivision of the Paleogene Periodaccording to theICS, as of January 2013.
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