Quaternary

EtymologyName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitPeriodStratigraphic unitSystemTime span formalityFormalLower boundary definition

• Base of magnetic polarity chronozone C2r (Matuyama)
• Extinction of the HaptophytesDiscoaster pentaradiatus and Discoaster surculus

Lower boundary GSSPMonte San Nicola Section, Gela, Sicily, Italy
37°08′49″N14°12′13″E / 37.1469°N 14.2035°E / 37.1469; 14.2035Lower GSSP ratified2009 (as base of Quaternary and Pleistocene)Upper boundary definitionPresent dayUpper boundary GSSPN/AUpper GSSP ratifiedN/AAtmospheric and climatic dataMean atmospheric O₂ contentc. 20.8 vol %
(100% of modern)Mean atmospheric CO₂ contentc. 250 ppm
(0.9 times pre-industrial)Mean surface temperaturec. 14 °C
(0.5 °C above pre-industrial)

The Quaternary ( , US also ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the Phanerozoic eon. It follows the Neogene Period and spans from 2.6 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.6 million years ago to 12 thousand years ago) and the Holocene (12 thousand years ago to today); a proposed third epoch, the Anthropocene, was rejected in 2024 by International Union of Geological Sciences (IUGS), the governing body of the International Commission on Stratigraphy (ICS).

The Quaternary is typically defined by the Quaternary glaciation, the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused.