Dating in the cradle

The new research published today in Nature by an international research team – including researchers from the Department of Archeology and History at the University of La Trobe and the School of Earth University of Melbourne Science – is the first to provide a comprehensive chronology of human evolution within the cradle of humanity. in South Africa.

Led by the University of Cape Town, the research also highlights the climatic conditions of our early ancestors in the region.

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, who has conducted research and excavations on many sites, said that "if the South African record was the first to show that Africa was the starting point of the Man, the complexity of the caves and the difficulty of dating them meant that the South African record remained difficult to interpret. "

"In this study, we show that runoff stones in caves can act almost like the volcanic layers of East Africa, forming simultaneously in different caves, allowing us to directly link their sequences and fossils to a regional sequence, "said Professor Herries. .

Professor Jon Woodhead of the University of Melbourne said the research results show that

"The Cradle Caves only date from six specific periods, about 3.2 to 1.3 million years ago,"

Dr. Robyn Pickering, Principal Researcher at the University of Cape Town, said: "Unlike previous dating work, which often focused on a cave, sometimes even a cave chamber, we provide direct ages for eight caves and one cave. model the age of all the fossils of the whole region.

"Now we can relate the results of different 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 site in the world for early humans and is home to nearly 40% of all known ancestor fossils, including the famous skull of Australopithecus africanus nicknamed Mrs Ples.

With the help of an ultramodern uranium lead dating developed at the University of Melbourne, researchers analyzed 28 layers of Flowstone detected between fossil-rich sediments in eight caverns located in the cradle. 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," said Dr. Pickering.

"We know that large flows only grow in caves during wet periods, when it rains more outside the caves. By dating the flow stones, we identify these periods of increased rainfall. So we know that during the in – between, 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, human fossils are only preserved during the drier periods kept in caves, thus distorting the record of human evolution.

This new document, funded in part by the ARC DECRA and Future scholarships of Dr. Pickering and Prof. Herries, is the result of more than a decade of work and brings together a team of 10 scientists from Australia, South Africa and the United States. Much of the analysis of dating has been done at the University of Melbourne, which remains a world leader in this type of analysis. These results bring the cradle back to the forefront and open up new opportunities for scientists to answer complex questions about the history of humanity in the region.

"Robyn and his team have greatly contributed to our understanding of human evolution," said paleoanthropologist Professor Bernard Wood, of the George Washington University's Center for Advanced Studies in Human Paleobiology. -United. l & # 39; study.

"This is the most important step forward since the discovery of the fossils themselves. Fossil dates matter a lot. The value of the evidence in Southern Africa has been multiplied by the present exemplary study of its temporal and depositional context ".