Older than Lucy
Since 2015, the international team working to date Little Foot has revealed its (old) age. 3.67 million years is the age Little Foot has finally been given. This result was made possible by a close collaboration between South African, American, Canadian and French scientists. The Australopithecine of the Silberberg Grotto is thus older than the famous 3.2 million year-old Lucy (East Africa).
Technical progress
The years spent by Laurent Bruxelles to unravel the stratigraphic layer cake of the Silberberg Grotto were put to good used by Marc Caffee (PRIME laboratory of Purdue University, United States) to improve the cosmogenic dating method. Now knowing which sediments to date, Darryl Granger (Purdue University) and Ryan Gibbon (University of New Brunswick, Canada) applied this method in an optimal manner to the samples collected at Sterkfontein.
Cosmic rays
The cosmogenic dating method is based on measurements of radioactive isotopes, such as Aluminim-26 and Beryllium-10, whose minerals are charged under the influence of cosmic rays while they were on the surface. After they are buried, in this case in the Silberberg Grotto, the minerals discharge their isotopes at a known rate.
Several samples
Ron Clarke (left) and Laurent Bruxelles in the Silberberg Grotto, with the fossil bones of Little Foot still cemented in the breccia
© Richard Maire, CNRS
The researchers applied this dating method to eleven samples collected over the last decade in the cave. Nine of them yielded coherent dates of 3.67 million years (plus or minus 0.16 million years). Little Foot is therefore as old as the first Australopithecus afarensis specimens at Laetoli (Tanzania) and Woranso-Mille (Ethiopia). This discovery and its dating confirm that South Africa is a potential cradle of Humankind, along with East Africa.