Revised ages of South African Australopithecus fossils

Early hominin species is 1 million years older than scientists previously thought.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES—Dating of a cave infill in South Africa that has yielded numerous Australopithecus fossils reveals that the fossils are older than previously thought and that the South African individuals were contemporaneous with Australopithecus afarensis in East Africa. Sterkfontein cave in South Africa is a treasure trove of Australopithecus fossils, often thought to be younger than A. afarensis, which lived in East Africa. Darryl E. Granger and colleagues calculated the ages of the Sterkfontein rocks in which the fossils are found by measuring the amounts of aluminum-26 and beryllium-10 isotopes in rocks containing quartz. The rare isotopes were formed by high-energy cosmic rays while the rocks were at the surface and decayed after they were buried in the cave with the fossils. The cosmogenic isotopes yielded an age of around 3.4-3.7 million years, older than the previously determined age of 2.1-2.6-million-years. The previous age was derived from calcite flowstones, which were intrusions into the fossil-bearing formation, leading to an underestimation of the fossils’ age. According to the authors, the revised age places South African Australopithecus as a contemporary of A. afarensis and other early Australopithecus species, expanding the diversity of hominin morphologies and habitats in the mid-Pliocene Epoch.


Female Australopithecus Sts 71, discovered in 1947 from Member 4 at Sterkfontein, South Africa and newly dated to 3.4-3.6 million years. Jason L. Heaton, Birmingham-Southern College, Birmingham, Alabama


‘Mrs. Ples’ (Sts 5), discovered at Sterkfontein, South Africa in 1947, now shown to be contemporaneous with Lucy’s species in East Africa. Jason L. Heaton, Birmingham-Southern College, Birmingham, Alabama


Article Source: PNAS news release.

*“Cosmogenic nuclide dating of Australopithecus at Sterkfontein, South Africa,” by Darryl E. Granger et al., Proceedings of the National Academy of Sciences, 27-Jun-2022.



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