Age· The columns of time

Before Sapiens

350 ka → 315 ka

This opening band covers the 35,000 years before the oldest fossils attributed to Homo sapiens, about 315,000 years ago.

Opening band of the timeline, prior to the appearance of the oldest fossils attributed to Homo sapiens. It covers the thirty-five thousand years preceding that limit and supplies the term of comparison without which the beginning of the species would not be measurable.

What the evidence shows

The right-hand limit of the band proceeds from the site of Jebel Irhoud, in Morocco, where heated flints were dated by thermoluminescence to 315,000 years, with an uncertainty of 34,000 years. The method dates the thermal event and not the material: natural radioactivity in the sediment progressively traps electrons in the crystals of the flint, and heat releases them as light, so that a flint fallen into a hearth had its counter reset to zero that day; heated in the laboratory, it gives back light whose intensity measures what has accumulated since. The associated human remains, from at least five individuals, present a face and jaw already conforming to our own on a braincase that does not. The boundary therefore designates not the appearance of the species, but the oldest assemblage complete enough to identify it.

Bounds and conventions

Two uncertainties of different nature are superimposed. The measurement carries an explicit error of 34,000 years, bounded and quantified. The definition carries none of that kind: a species has no date of appearance, and each new site may move this limit. Jebel Irhoud itself moved it by more than a hundred millennia when it was redated in 2017.

Porch: the lineage preceding the species. The 315 ka boundary is the dating of Jebel Irhoud (315 ± 34 ka) and not a sharp threshold, which the hatching represents.