Age· The columns of time
Chibanian
774 ka → 129 ka
The only unit of the geological time scale named after a place in Japan, and the age in which our own species appears.
What the evidence shows
The Chiba section, on the Boso Peninsula, was ratified in 2020 after a long contest with European candidates, and puts the base at about 774,000 years: the level falls inside Marine Isotope Stage 19 and sits close to the Matuyama-Brunhes magnetic reversal at roughly 773,000 years, the last time the Earth's magnetic field flipped. The age holds the appearance of our own species, around 300,000 years ago in Africa, and it holds the others: Neanderthals across Europe and western Asia, at least some of them in groups where close kin bred together, Denisovans in Asia, and on Flores a population of small-bodied hominins. None of these lineages was alone, and the genomes of living people still carry the record of the meetings between them.
Bounds and conventions
Its boundary is fixed, and the magnetic reversal beside it is one of the best-dated events of the Quaternary. The appearance of our species is not a date but a judgement about which traits count: the Moroccan fossils, dated to 315,000 years give or take 34,000, are the oldest so assigned, their faces already ours and their braincases still long and low.
GSSP of the Chiba section, ratified in 2020.
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.
- Hublin et al. (2017), Nature · New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens
- Prüfer et al. (2014), Nature · The complete genome sequence of a Neanderthal from the Altai Mountains