Age· The columns of time
Gelasian
2.6 Ma → 1.8 Ma
The age that begins the Quaternary, added to it in 2009: the northern ice sheets take hold, and hominins are already leaving Africa.
What the evidence shows
Its boundary, at 2.58 million years, is a golden spike in Sicily aligned with Marine Isotope Stage 103 and lying close to the Gauss-Matuyama magnetic reversal. It was transferred in 2009, when the base of the Quaternary and of the Pleistocene was lowered from 1.8 million years to take it in: an age that had belonged to the Pliocene changed epochs by a vote. What it contains justifies the move, since this is when ice sheets become a permanent feature of the northern hemisphere. And it holds the oldest departure yet found: long before our own species existed, hominins walked out of Africa and across Asia, leaving stone tools on the Chinese Loess Plateau by about 2.1 million years, ahead of the well-dated travellers of Dmanisi in the Caucasus, small in body and small in brain.
Bounds and conventions
The boundary is well defined, though its stated relation to the Gauss-Matuyama magnetic reversal has itself been corrected in the literature since it was first published. No hominin bones were found with the Chinese tools, so who made them is unknown, and estimates of when hominins first left Africa move with each new site rather than converging.
GSSP ratified in 2009; it also defines the base of the Pleistocene and of the Quaternary.
Sources
- Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
- Head, M. J. (2019). Formal subdivision of the Quaternary System/Period: Present status and future directions. Quaternary International 500, 32–51.
- Zhu et al. (2018), Nature · Hominin occupation of the Chinese Loess Plateau since about 2.1 million years ago
- Lisiecki & Raymo (2005), Paleoceanography · A Pliocene-Pleistocene stack of 57 globally distributed benthic oxygen isotope records