A new study by an international team of scientists led by a geochemist at the University of Cape Town, Robin Pickering, was the first to provide a time frame for fossils from caves in the Cradle of Humanity. It also sheds light on the climatic conditions of our early ancestors in the area.
Published online in the magazine Nature On November 21, 2018, the paper corrects assumptions that caves rich in the fossil region can never be connected with each other. In fact, the study suggests cradle fossils for up to six specific periods of time.
“Unlike previous work with dates, which often focused on one cave, sometimes even on one cave chamber, we provide direct ages for eight caves and a model to explain the age of all fossils of the entire region,” says Dr. Robin Pickering.
“Now we can link the results of individual caves and create the best picture of evolutionary history in southern Africa.”
The cradle of mankind is a World Heritage site, consisting of complex fossil caves. This is the world's richest early hominin site and home to nearly 40% of all known human ancestral fossils, including the famous Australopithecus africanus skull, dubbed Mrs. Ples.
Using the uranium-lead dating, the researchers analyzed 28 layers of reservoir cover, which were found sandwiched between rich fossil sediments in eight caves across the Cradle. The results showed that the fossils in these caves date back to six narrow time windows between 3.2 and 1.3 million years ago.
“Streams are the key,” says Pickering. “We know that they can only grow in caves during wet times when there is no more rain outside the cave. When we meet with stone stones, we choose these times of increased precipitation. Therefore, we know that in the intervals when the caves were open, the climate was drier and more like what we are currently experiencing. ”
This means that early hominins living in the Cradle experienced great changes in the local climate, from more humid to drier conditions, at least six times between 3 and 1 million years ago. However, only drier times are preserved in the caves, distorting the history of the early evolution of man.
Until now, the lack of methods for dating the cradle fossils has made it difficult for scientists to understand the relationship between hominin species in Eastern and Southern Africa. Moreover, the South African record was often considered indisputable compared to East Africa, where volcanic ash layers allow for high-resolution encounters.
Professor Andy Harris, co-author of research at the University of La Trobe in Australia, notes that “while the South African record was the first to show Africa as the source of people, the complexity of the caves and the difficult acquaintance with them meant that the South African record is still difficult interpret. "
“In this study, we show that flowing stones in caves can act like the volcanic layers of East Africa, simultaneously forming in different caves, which allows us to directly link their sequences and fossils in a regional sequence,” he says.
Dr. Pickering began dating the Cradle Caves back in 2005 as part of his Ph.D. study. 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 USA. The results bring the cradle back to the foreground and open up new opportunities for scientists to answer complex questions about human history in the region.
“Robin and her team have made a great contribution to our understanding of human evolution,” says leading paleoanthropologist Professor Bernard Wood of the Center for Advanced Study of Human Paleobiology at George Washington University in the United States, who is not the author of the studies.
“This is the most important progress to be made since the fossils themselves were discovered. Dates of fossils are important. The value of South African evidence has been multiplied by this exemplary study of its temporal and sedimentary context. ”
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Robin Pickering et al., U-Pb flow rates limit the South African early hominin record for dry climatic phases, Nature (2018). DOI: 10.1038 / s41586-018-0711-0