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Paleogene | |||||||||||||
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![]() Map of Earth as it appeared 50 million years ago during the Eocene, Ypresian stage[citation needed] | |||||||||||||
Chronology | |||||||||||||
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Etymology | |||||||||||||
Name formality | Formal | ||||||||||||
Alternate spelling(s) | Palaeogene, Palæogene | ||||||||||||
Usage information | |||||||||||||
Celestial body | Earth | ||||||||||||
Regional usage | Global (ICS) | ||||||||||||
Time scale(s) used | ICS Time Scale | ||||||||||||
Definition | |||||||||||||
Chronological unit | Period | ||||||||||||
Stratigraphic unit | System | ||||||||||||
Time span formality | Formal | ||||||||||||
Lower boundary definition | Iridium enriched layer associated with a major meteorite impact and subsequent K-Pg extinction event. | ||||||||||||
Lower boundary GSSP | El Kef Section, El Kef, Tunisia 36°09′13″N 8°38′55″E / 36.1537°N 8.6486°E | ||||||||||||
Lower GSSP ratified | 1991[3] | ||||||||||||
Upper boundary definition |
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Upper boundary GSSP | Lemme-Carrosio Section, Carrosio, Italy 44°39′32″N 8°50′11″E / 44.6589°N 8.8364°E | ||||||||||||
Upper GSSP ratified | 1996[4] | ||||||||||||
Atmospheric and climatic data | |||||||||||||
Mean atmospheric O2 content | c. 26 vol % (125 % of modern) | ||||||||||||
Mean atmospheric CO2 content | c. 500 ppm (1.8 times pre-industrial) | ||||||||||||
Mean surface temperature | c. 18 °C (4.5 °C above pre-industrial) |
The Paleogene Period (IPA: /ˈpeɪli.ədʒiːn, -li.oʊ-, ˈpæli-/ PAY-lee-ə-jeen, -lee-oh-, PAL-ee-; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 Ma (million years ago) to the beginning of the Neogene Period 23.03 Ma. It is the first period of the Cenozoic Era and is divided into the Paleocene, Eocene, and Oligocene epochs. The earlier term Tertiary Period was used to define the time now covered by the Paleogene Period and subsequent Neogene Period; despite no longer being recognized as a formal stratigraphic term, "Tertiary" still sometimes remains in informal use.[5] Paleogene is often abbreviated "Pg", although the United States Geological Survey uses the abbreviation "Pe" for the Paleogene on the Survey's geologic maps.[6][7]
During the Paleogene period, mammals continued to diversify from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.[8]
The Period is marked by considerable changes in climate from the Paleocene–Eocene Thermal Maximum, through global cooling during the Eocene to the first appearance of permanent ice sheets in the Antarctic at the beginning of the Oligocene.[9]
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