Research by scientists from the Human Evolution Research Institute (HERI) at the University of Cape Town (UCT) provides evidence that Bolt’s Farm, an area of the South African Cradle of Humankind, is far younger than previously thought.
The work, published in the prestigious Journal of Human Evolution, uses a multi-disciplinary approach of sediment analysis, palaeomagentism and uranium-lead dating to age the cave deposits between 2.27 and 1.70 million years old, correcting previous work which overestimated the age by around 2 million years.
“Our research applies multiple lines of evidence to reliably dispel the long-held assumption that Bolt's Farm is a site of great antiquity,” says lead author Dr Tara Edwards, a HERI postdoctoral research fellow from the Department of Geological Sciences at UCT.
“This finding helps us more accurately assess the ages of sites within the Cradle, including fossils that directly impact our understanding of human origins.”
Bolt’s Farm is a cave system found in the Cradle of Humankind World Heritage Site in South Africa. It is an important source of fossils, with various species of Plio-Pleistocene fauna, including primates and big cats. It is also home to a novel species of rat, Euryotomys bolti (E. bolti), found nowhere else.
Early research had dated the small cave called Waypoint 160 at Bolt’s Farm at about 4.5 million years, making it far older than other Cradle sites. That work, however, relied on the fossilised remains of the novel E. bolti species and comparing it to other fossil sites in South Africa.
In this new study, Edwards and her team present an analysis of sedimentary rock deposits from within the cave, including uranium-lead dating of flowstones, palaeomagnetic analysis, and facies analysis.
“No previous study uses multiple lines of evidence to date Bolt’s Farm, so this research really highlights the importance of multidisciplinary work for painting a holistic and cohesive picture of the past,” says Edwards.
Th findings not only give a more robust date for Bolt’s Farm but make it possible for the first time to compare it with other fossil-bearing deposits within the region. They also redefine the suggested age of the E. bolti species, dating it almost 2 million years younger than previously assumed.
Indeed, the fossil-bearing caves in the Cradle are the richest early hominin sites in the world. They are home to nearly 40% of all known human ancestor fossils, including the famous Australopithecus africanus skull nicknamed Mrs Ples.
“We know the Cradle holds important clues about our human evolution and researchers should be invigorated to explore the region more,” says Edwards.
“But as it stands, all of our work using multidisciplinary sources over the last few years show no evidence for any sites in the Cradle older than 3.20 million years ago.”
According to HERI Co-director Dr Robyn Pickering, a co-author on the study, this is significant because it debunks assumptions that sites like Sterkfontein Caves, where numerous early hominin remains have been found, preserve deposits and fossils older than this.
“It is becoming increasingly unlikely that Sterkfontein is as old as claimed, and this new study is yet another compelling piece of evidence against the presence of very old caves and fossils in the Cradle,” Pickering says.