Age· The columns of time

Gelasian

2.6 Ma → 1.8 Ma

The Gelasian, from 2.6 to 1.8 million years ago, opens the Quaternary, to which it was attached by a vote in 2009: the northern ice sheets became permanent and hominins were already leaving Africa.

Opening age of the Quaternary, attached to that period by a vote in 2009, in which the northern hemisphere ice sheets become permanent and hominins already leave Africa.

What the evidence shows

Its limit, at 2.58 million years, is a golden spike in Sicily, aligned on marine isotope stage 103 and close to the Gauss-Matuyama magnetic reversal, a change in the polarity of the Earth's field recorded simultaneously worldwide and therefore usable to correlate distant sequences. The age changed epoch in 2009, when the base of the Quaternary and of the Pleistocene moved from 1.8 to 2.58 million years to include it: it had previously belonged to the Pliocene. Its contents justify that attachment, ice sheets becoming at this point a permanent feature of the northern hemisphere. It also carries the oldest known departure from Africa: stone tools on the Chinese Loess Plateau, at Shangchen, are dated to about 2.1 million years, earlier than the occupants of Dmanisi, in the Caucasus, small in body and in brain.

Bounds and conventions

The limit is well defined, although the relation attributed to it with the Gauss-Matuyama reversal has been corrected in the literature since publication. No hominin bone accompanies the Chinese tools, so their makers remain unknown, and estimates of the first departure from Africa shift with each new site instead of converging.

GSSP ratified in 2009; it also defines the base of the Pleistocene and of the Quaternary.