Eocene

EtymologyName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitEpochStratigraphic unitSeriesTime span formalityFormalLower boundary definitionStrong negative anomaly in δC values at the PETMLower boundary GSSPDababiya section, Luxor, Egypt
25°30′00″N32°31′52″E / 25.5000°N 32.5311°E / 25.5000; 32.5311Lower GSSP ratified2003Upper boundary definition of Planktonic ForaminifersHantkenina and Upper boundary GSSPMassignano quarry section, , Ancona, Italy
43°31′58″N13°36′04″E / 43.5328°N 13.6011°E / 43.5328; 13.6011Upper GSSP ratified1992

The Eocene (IPA: ) is a geological epoch that began about 56 million years ago (Ma). It is the second epoch of the PaleogenePeriod in the modern CenozoicEra. The end point of the Eocene is the Eocene-Oligocene transition (EOT), between 33.9 and 33.4 Ma. Precise boundaries between the epochs are sometimes given at 33.9 or 33.7 Ma.

The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by a brief period in which the concentration of the carbon isotopeC in the atmosphere was exceptionally low in comparison with the more common isotope C. The average temperature of Earth at the beginning of the Eocene was about 27 degrees Celsius. The end is set at a major extinction event called the Grande Coupure (the "Great Break" in continuity) or the Eocene–Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified, though their exact dates are slightly uncertain.