It was thanks to recently-developed technology that an international team of scientists was able to announce recently the determination of new dates for the famous Little Foot skeleton excavated from the globally-famous Sterkfontein Caves, in South Africa’s Gauteng province. The team comprises researchers from South Africa, Canda, France and the US. It also announced new dates for tools from the Oldowan culture, also found at Sterkfontein.
Using the new technique, the team was able to determine that Little Foot, an individual of the hominid species Australopithecus Prometheus, dates from 3.67-million years ago, give or take 160 000 years. The unrelated Oldowan quartz tools have now been dated to 2.18-million years, plus/minus 210 000 years.
Previously, proposed dates for Little Foot had ranged from 2.2-million years to nearly 4-million years. These estimates had been derived using different dating techniques. The Oldowan tools had originally been dated to about 1.7- million years ago to 2-million years ago, based on apparently associated animal fossils.
The South African members of the team are Professors Ron Clarke (recently retired as director of excavations at Sterkfontein and now honorary reader in palaeoanthropology at the University of the Witwatersrand (Wits)) and Kathleen Kuman (Wits School of Geography, Archaeology and Environmental Studies). Clarke was the original discoverer of Little Foot, while Kuman is a specialist in the Stone Age. The overseas members are Professor Ryan Gibbon of the University of New Brunswick, Canada (who obtained his PhD at Wits); Dr Laurent Bruxelles of the Institut National de Recherches Archéologiques Préventives at the University of Toulouse–Jean Jaurés, France; and Professor Darryl Granger of Purdue University, in Indiana, US.
It was the Purdue Rare Isotope Measurement Laboratory (PRIME Lab) that made the new datings. This is a US national facility for accelerator mass spectrometry (AMS). Granger is a member of PRIME Lab and the project also benefited from the expertise of the lab’s director, physics Professor Marc Caffee.
The new dates were obtained using the recently developed gas-filled magnet detector, which has been added to the AMS system. The AMS was used to detect cosmogenic nuclides in the rock in which the fossils and tools were embedded. These nuclides are created by cosmic rays, which constantly bombard the earth.
In particular, the isotopes Aluminium-26 and Beryllium-10 are sought, for these are created in measurable amounts within quartz by the interaction between the cosmic rays and the silica and oxygen in the rock. But this process can only take place if the quartz is on or near the surface. Should the quartz be, for example, eroded by water and washed into a deep cave, the creation of the two isotopes will stop and, because they are radioactive, decay will set in. It is this radioactive decay which allows the dating of the deposits. This is what happened at Sterkfontein.
AMS is the only way to measure these cosmogenic nuclides. “This [the gas-filled magnet detector] allows us to measure Aluminium-26, in particular, up to ten times better than before,” explained Granger at a videoconference. Aluminium-26 is more common than Beryllium-10; the former builds up at a rate 6.8 times faster than the latter. “The new AMS technologies will allow improved dating at Sterkfontein and other sites around the world.”
The result shows that Little Foot is about 500 000 years older than the famous Lucy fossil from East Africa. Clarke pointed out that this meant that three early forms of hominid existed at the same time: Australopithecus Prometheus (Little Foot), Australopithecus afarensis (Lucy) and Kenyanthropus platyops.
As for the unrelated and much later Oldowan culture (named after East Africa’s renowned Olduvai Gorge, where its first tools were first found), “[w]e [now] know this [Sterkfontein] Oldowan is an older Oldowan, an earlier stage,” noted Kuman. “Quartz . . . flakes very easily and makes very sharp cutting edges. Quartzite produces stronger flake edges, for heavier duty tasks.” The Oldowan was a “simple and expedient tool industry”. It is not yet clear what species was responsible for these tools, although there are indications it could have been Homo habilis.