Researchers say they have confirmed their theory that humans were active in a cavern in South Africa far earlier than initially thought, dating occupation of the Wonderwerk Cave to 1.8 million years ago, the Hebrew University of Jerusalem said in a statement Monday.
The assessment by the team of geologists and archaeologists from the university and the University of Toronto pushes back the prehistoric past dwelling in the desert cave by nearly a million years.
Whereas ancient humans are known to have been using basic stone tools, known as Oldowan, already 2.5 million years ago, that activity was out in the open. Wonderwerk, meaning “miracle” in Afrikaans, holds the earliest evidence anywhere in the world of such tool use inside a cave.
The results of their study was published in Quaternary Science Reviews.
“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,” the lead author of the study, Professor Ron Shaar of Hebrew University’s Institute of Earth Sciences, said in the statement. “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.”
Over a decade ago, members of the team, led by Toronto University researcher Michael Chazan, first estimated dwelling in the cave to have been around 2 million years ago, but the idea was rejected by most scholars, according to Liora Kolska Horwitz, of the Hebrew University’s National Natural History Collections.
In the latest study, the researchers used delicate laboratory analysis to unlock faint traces of cosmic rays and the ancient alignment of the earth’s magnetic field to date when different layers of sediment were blown into the cave, which extends 140 meters into the side of a hill, and the small fragments left over from human activity embedded in the layers.
Researchers were able to identify the period when the cave dwellers made the switch, over 1 million years ago, from using sharp flakes of stone and other such chopping tools to the use of early handaxes. They could also see when prehistoric ancestors began to make deliberate use of fire, a discovery of particular significance, the statement said, as other examples of early fire in open spaces are less reliable due to the possible role of wildfires in producing charred remains.
Wonderwerk offered up a range of fire remnants including burnt bone, sediment, and ash.
The process of dating cave deposits in the study of human evolution is challenging and the team analyzed a 2.5-meter-thick sedimentary layer that was found to contain stone tools, animal remains, and fire remnants.
They used two methods, paleomagnetism and burial dating.
Among the minerals that can be found in clay is iron, an element that is influenced by magnetic fields. Clay particles gain a magnetic alignment in line with the earth’s and researchers examining samples from the cave floor were able to deduce clues about the orientation of the earth’s magnetic field when they were buried.
“We carefully removed hundreds of tiny sediment samples from the cave walls and measured their magnetic signal,” said Shaar. “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.”
Every half a million years or so, the earth’s magnetic field changes direction, flipping from one pole to the other.
“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 said.
Another team member, Prof. Ari Matmon, director of Hebrew University’s Institute of Earth Sciences, examined quartz particles that gave clues as to when they were brought to the cave, due to certain isotopes they contain that build up when the quartz is exposed to cosmic rays on the ground outside, and then decayed over time when deposited inside the 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,” Matmon explained in the statement.
The discoveries have “far-reaching implications,” the university said in the statement, as they provided “an important step toward 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,” the statement said.