Robyn Pickering, University of Cape Town, South Africa
Dating the rocks and shaking the tree: geochronology and decolonization of human evolution in South Africa
The Cradle of Humankind (Cradle) in South Africa is home to a rich collection of early human (hominin) fossils, preserved in dolomite paleocaves. For decades these deposits were seen as undateable, due to the lack of volcanic deposits found in similar aged fossil bearing sediments in eastern Africa. However, flowstones (horizontally bedded calcium carbonate deposits) are ubiquitous features at the cave sites. These flowstone serve the dual purpose of providing ages for the fossilferous sediments sandwiched between them (via U-Pb dating) and as indicators of past climate regimes by their presence alone, being associated with increased effective precipitation. Flowstones from eight caves across the Cradle have produced a total of 28 U-Pb ages and a record spanning from 3.2 – 1.3 Ma. This is the first direct chronology of this region and represents a major advance in understanding both the evolution of the early hominins and other fauna, as well as the landscape and climate. The new geochronology data, together with field observations of stacked, alternating layers of flowstone and externally derived clastic sediments at all the cave sites, suggest that the fossil-bearing deposits carry an inherent dry phase bias, as fossil accumulation is restricted to the drier phases in between flowstone formation. While they represent clear temporal gaps in the South African fossil record, the flowstones themselves provide valuable insights into local and pan-African climate variability. The context and history of human evolution in South Africa is deeply rooted in the country's complicated past. Rather than shy away from the imbedded racism in human evolution, particularly in South Africa, we need to lean into our own discomfort and work on the decolonization of our scientific practice. From the language we use, to the teams we build, decolonization is both urgent and necessary.
About the speaker:
Robyn is an isotope geochemist with leanings towards palaeoanthropology and archaeology. Her research seeks to understand where, and most importantly when, our early human ancestors evolved and what their environments were like. She works specifically on developing the U-series technique to date carbonates associated with early human fossils. Robyn got her PhD from the University of Bern in 2009 and spent six years at the University of Melbourne as a postdoc working on uranium-lead dating hominin cave sites. This pioneering work resulted in the first, direct time line for the early hominin fossil record from South Africa. Robyn is now a senior lecturer at the University of Cape Town and Director of the Human Evolution Research Institute (HERI). She is passionate about making the study of our human past a more welcoming, inclusive and diverse space. Robyn is also a mother of two, a keen knitter and beginner baker.
Dr Bronwen Konecky, Washington University, St Louis, MO, USA