A research team based at La Trobe University and The University of Melbourne has conducted a ten-year study into gaps in the fossil record of early humans from the so-called ‘Cradle of Humankind’ caves in South Africa. The team—which includes Dr Robyn Pickering, ARC Discovery Early Career Researcher Award (DECRA) recipient, Professor Andy Herries, supported through the ARC Future Fellowships scheme, and ARC Australian Laureate Fellowship recipient, Professor Jon Woodhead—has discovered that the fossil record is biased towards periods of drier climate, suggesting there might be significant holes in our understanding of the evolution of early humans.

The caves in which the fossils are found have significantly eroded over the years, and the expected age range of the fossils makes dating the fossils difficult. In recent years, one method that has shown to be successful is the uranium-lead dating of the flowstone (a calcium carbonate cave formation that grows during wet periods) that occurs in layers between fossil-rich cave sediment. The researchers found that flowstones formed in multiple caves in the region at the same time, allowing the various sequences to be directly correlated for the first time. Moreover, the work suggests that periods when fossils were deposited in the caves were biased towards drier periods when flowstone was not forming.

The research team included 10 scientists from Australia, South Africa and the US and received additional support through the ARC’s Discovery Projects scheme.

Uranium-lead dating revealed that the fossils in these caves date to six narrow time-windows between 3.2 and 1.3 million years ago.

Image: The deroofed Drimolen Palaeocave deposits in South Africa from which flowstones were dated. In South Africa, such caves have yielded the remains of our early ancestors between 3.1 and 1.3 million years ago.
Credit: Professor Andy I.R. Herries.