Age· The columns of time
Before Sapiens
350 ka → 315 ka
The timeline does not begin with the species; it begins a little before, so that the beginning has something to be measured against. This band is that margin: thirty-five thousand years of running room, ending at the oldest fossils a specialist would call ours.
What the evidence shows
The date at its right-hand edge comes from Jebel Irhoud in Morocco, where flints heated in ancient fires were dated by thermoluminescence to 315,000 years, give or take 34,000, and where the human remains found with them show a face and a jaw already like ours on a braincase that is not. That is what the boundary marks: not a moment when the species appeared, but the oldest place where enough of it has been found together to be recognised. The hatching along the border says as much.
Bounds and conventions
Two kinds of uncertainty meet here, and they are not the same size. The measurement carries an error of 34,000 years, which is honest and bounded. The concept does not: a species has no first morning, and every new site can move this edge. Jebel Irhoud itself moved it by more than a hundred millennia when it was redated in 2017.
The porch: the lineage that precedes the species. The 315 ka boundary is the date of Jebel Irhoud (315 +/- 34 ka), not a sharp threshold, which is why the band is hatched.