Agriculture is not the official definition of the age. But it is good enough. Likely related to the official end of glaciations thing.
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The Quaternary is the current geological period, beginning 2.58 million years ago. It contains the Pleistocene and Holocene epochs. Repeated major glacial cycles make its marine and continental records important for studying climate variability.[ref]
International Chronostratigraphic Chart by International Commission on Stratigraphy (2026-06). Cenozoic and Mesozoic columns; numerical ages in Ma