Determining the date of human deposits in ancient caves is one of the greatest challenges in paleo-anthropology. It is, in effect, a study of human evolution. Few sites in the world preserve a continuous archaeological record spanning millions of years, but the Wonderwerk Cave – located in South Africa’s Kalahari Desert – is one of those rare sites. And Israelis at the Hebrew University of Jerusalem (HUJI), with colleagues at the University of Toronto, have been involved in this endeavor.
Meaning “miracle” in the South African language of Afrikaans, Wonderwerk Cave has been identified as potentially the earliest cave occupation in the world and the site of some of the earliest indications of fire use and tool making among prehistoric humans.
The new research, just published in the journal Quaternary Science Reviews under the title “Magnetostratigraphy and cosmogenic dating of Wonderwerk Cave: New constraints for the chronology of the South African Earlier Stone Age,” was led by Prof. Ron Shaar at HUJI’s Institute of Earth Sciences.
“The precise ages of the Wonderwerk sediments are crucial for our understanding of the timing of critical events in hominin biological and cultural evolution in the region, and its correlation with the global paleontological and archaeological records,” they wrote.
The team confirmed the record-breaking date of this spectacular site. “We can now say with confidence that our human ancestors were making simple Oldowan stone tools inside the Wonderwerk Cave 1.8 million years ago,” declared Shaar. “Wonderwerk is unique among ancient Oldowan sites, a tool-type first found 2.6 million years ago in East Africa, precisely because it is a cave and not an open-air occurrence.”
The geologists and archaeologists were able to successfully establish the shift from Oldowan tools (mainly sharp flakes and chopping tools) to early handaxes over a million years ago, and to date the deliberate use of fire by our prehistoric ancestors to a million years ago in a layer deep inside the cave. This is a particularly significant because other examples of early use of fire come from open-air sites where the possible role of wildfires cannot be excluded. In addition, Wonderwerk contained a full array of fire remnants – burnt bone, sediment, tools and the presence of ash.
To overcome the dating challenge, the team analyzed a 2.5-meter-thick layer of sediment that contained stone tools, animal remains and fire remnants using paleomagnetism and burial dating. “We carefully removed hundreds of tiny sediment samples from the cave walls and measured their magnetic signal,” recalled Shaar.
Magnetization occurred when clay particles that entered the cave from outside settled on the prehistoric cave floor, thereby preserving the direction of the earth’s magnetic field at that time. “Our lab analysis showed that some of the samples were magnetized to the south instead of the north, which is the direction of today’s magnetic field. Since the exact timing of these magnetic “reversals” is globally recognized, it gave us clues to the antiquity of the entire sequence of layers in the cave,” Shaar added.
Prof. Ari Matmon, director of HUJI’s the Institute of Earth Sciences, relied on a secondary dating method to further confirm when the earliest “humans” may have occupied the site. “Quartz particles in sand have a built-in geological clock that starts ticking when they enter a cave. In our lab, we are able to measure the concentrations of specific isotopes in those particles and deduce how much time had passed since those grains of sand entered the cave,” he explained.
The dating of prehistoric human activity at Wonderwerk Cave has far-reaching implications, the authors said. The co-directors of the Wonderwerk Cave project – Prof. Michael Chazan at the University of Toronto and Liora Kolska Horwitz at HUJI’s National Natural History Collections – explained that the findings at Wonderwerk “are an important step towards understanding the tempo of human evolution across the African continent. With a timescale firmly established for Wonderwerk Cave, we can continue studying the connection between human evolution and climate change, and the evolution of our early human ancestors’ way of life.”
On the southern edge of the Kalahari Desert, Wonderwerk Cave is also a place of great spiritual significance to local communities, attesting to the cave’s cultural importance for both past and present peoples. The Wonderwerk Cave Research Project is committed to protecting the site and to working with neighboring towns to develop the educational and cultural potential of this unique place.