Here we use isochron burial dating with cosmogenic aluminium-26 and beryllium-10 to show that the breccia containing St W 573 did not undergo significant reworking, and that it was deposited 3.67 ± 0.16 million years ago, far earlier than the 2.2 million year flowstones found within it This work results from a collaboration begun with T. AMS development and measurements were funded by National Science Foundation EAR1153689 to M.
(Toumaï) (1, 2) have changed substantially the understanding of early human evolution in Africa (1–4).This as well as the associated uncertainties is fully discussed in the Materials and Methods section.In this first attempt of calibration in a continental context, the calculated authigenic Be ages obtained in or close to the fossiliferous levels were compared with the ages estimated by using the evolutive degree of fossil mammal assemblages.At both localities, the evolutive degree of the associated fossil mammal assemblages allowed a biochronological estimation of the hominid remains: early Pliocene (3–3.5 Ma) at KT 12 and late Miocene (≈7 Ma) at TM 266. This chronological constraint is an important cornerstone both for establishing the earliest stages of hominid evolution and for new calibrations of the molecular clock. Localities investigated in this area include TM 266 and TM 254 (Fig. The Kollé (KL), Kossom Bougoudi (KB), and Koro Toro (KT) fossiliferous areas were specifically studied to calibrate the authigenic Be dating method by direct comparison with biochronological estimations of co-located mammalian assemblages.Fossiliferous localities investigated in these areas were KL, KB 1, and KT 12 (Fig. KT 12 (16°00′N, 18°53′E) is the site of locality, Toros-Menalla, Upper Miocene, Northern Chad).