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New research conducted by an international team of scientists led by the Isotope Geochemist at the University of Cape Town, Dr. Robyn Pickering, is the first to provide a chronology of fossils from caves located in the cradle of the island. 39; humanity. It also highlights the climatic conditions of our early ancestors in the region.
Posted online in the newspaper Nature on November 21, 2018, the work corrects the hypothesis that the fossil-rich caves of the region could never be connected to each other. In fact, research suggests that Cradle Cave fossils date back only to six specific periods.
"Unlike previous dating work, which often focused on a cave, sometimes even on a room, we provide direct ages for eight caves and a model to explain the age of all the fossils of the entire region," explains Dr. Robyn. Pickering.
"Now we can relate the results of separate caves and create a better picture of the history of evolution in southern Africa."
The cradle of humanity is a world heritage site consisting of complex caves containing fossils. It is the richest hominin site in the world and is home to nearly 40% of all known human ancestor fossils, including the famous skull of Australopithecus africanus nicknamed Mrs Ples.
Using lead-uranium dating, researchers analyzed 28 layers of Flowstone found sandwiched between fossil-rich sediments in eight cradle caves. The results revealed that fossils in these caves date from six narrow time windows between 3.2 and 1.3 million years ago.
"Flowstones are the key," says Pickering. "We know that they can only grow in caves during wet periods, when it rains more, and by dating the flow stones, we identify these periods of increased rainfall, so we know that during the interim period, when the caves were open, the climate was drier and more like what we are currently experiencing. "
This means that the first hominins living in the cradle have experienced great changes in the local climate, from the wettest to the driest, at least six times between 3 and 1 million years ago. However, only the driest periods are preserved in the caves, thus distorting the record of human evolution.
Until now, the lack of dating methods for cradle fossils prevented scientists from understanding the relationship between hominins from East and South Africa. In addition, South African records have often been considered indecipherable compared to East Africa where volcanic ash layers allow for high resolution dating.
Professor Andy Herries, co-author of the study at La Trobe University in Australia, notes that "if the South African record was the first to show that Africa is the point of Origin of the man, the complexity of the caves and their difficult dating meant that the South African record remained difficult to interpret ".
"In this study, we show that the circulation stones in the caves can act almost like the volcanic layers of East Africa, forming simultaneously in different caves, which allows us to directly connect their sequences and their fossils to a regional sequence, "he explains.
Dr. Pickering began attending Cradle Caves in 2005 as part of his PhD work. This new publication is the result of 13 years of work and brings together a team of 10 scientists from South Africa, Australia and the United States. The results bring the cradle back to the fore and provide scientists with new opportunities to answer complex questions about the history of humanity in the region.
"Robyn and his team have made a major contribution to our understanding of human evolution," said paleoanthropologist Professor Palaeoanthropologist Bernard Wood of George Washington University's Center for Advanced Studies in Human Paleobiology. in the USA. l & # 39; study.
"This is the most important step forward since the discovery of the fossils themselves. The date of the fossils is very important. The value of evidence for southern Africa has been multiplied by study by this exemplary study of its temporal and sedimentary context. "
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