Some of the most important fossils of humanity’s ancestors, discovered in South Africa in the last century, may be 1 million years older than previously thought, claims a study that has just been published by an international team of scientists. If the new analysis is correct, some of the australopithecines (apemen) found in the South African caves of Sterkfontein could have lived 3.4 million years ago.
The age exceeds that of the famous Lucy, female of the species Australopithecus afarensis who died in Ethiopia some 200,000 years later.
Sites in East Africa (including Ethiopian territory) and South Africa are by far the main source for understanding the evolution of australopithecines, primates that were fully bipedal (despite some differences from our way of walking), but they still had modest dimensions, up to 1.40 m in height.
These hominins (members of the closest lineage to man) also had small brains, comparable to those of modern chimpanzees, about a third the size of ours.
The new dates of the Sterkfontein rocks associated with the fossils came out in the latest issue of the scientific journal PNAS. The work was coordinated by Darryl Granger, from the Department of Atmospheric, Planetary and Earth Sciences at Purdue University (USA), and South African and European researchers also participate.
Obtaining reliable dates in the region is often a challenge because Sterkfontein’s cave system, formed from a limestone relief that looks more like Swiss cheese, produces layers of rock that are naturally difficult to interpret. Factors such as when the cave was influenced by external environmental conditions or groundwater that influenced the composition of the rock must be taken into account – factors that impact dating methods by creating an extremely complex stratigraphy (succession of layers).
The group led by Granger carried out a new analysis of this stratigraphic complexity, with the aim of determining which rock layers are really associated with the presence of the main australopithecine fossils in the caves. In addition, they dated the rock samples using a method that measures the transformation of radioactive chemical elements originally formed by cosmic ray bombardments — high-energy rays that reach Earth from space.
The arrival of cosmic rays, “hitting” the rocks and forming the radioactive chemical variants, can be compared to the moment when a stopwatch is reset and then starts counting time. The “zero”, in this case, is the initial amount of radioactive elements in the rock. As they transform into other elements at a known rate, you can tell how long the “chronometer” has ticked, hence the age of the rock and, in theory, the age of the fossils associated with it.
If the analyzes based on all this are confirmed, confirming the advanced age of the Sterkfontein hominins, it will be necessary to rethink the relationships that were imagined to exist between the different species of the genus. Australopithecus.
Previously, it was believed that the Australopithecus africanusa species that predominates in Sterkfontein, could descend from the Australopithecus afarensisthe species of Lucy, which would be more than 1 million years older.
With the shortening of the temporal distance between the two hominins, the descent relationship becomes less believable. However, this does not mean that the group arose in South Africa – at least for now, there are much older hominins of other species, over 4 million years old, in Ethiopia.
