Although separated by several thousand kilometers, southern and eastern Africa were, in a sense, a stone’s throw from each other ancient times. New evidence suggests that human ancestors in southern Africa fashioned teardrop-shaped stone hand axes 1.6 million years ago, nearly twice as long ago as many researchers thought and about the time such tools are known to have first appeared in eastern Africa.
Ryan Gibbon and his colleagues dated hand axes and related stone implements, collectively known as Acheulean artifacts, using measures of the relative decay of radioactive forms of aluminum and beryllium in quartz grains from the soil and gravel bearing the artifacts. Exposure to cosmic radiation causes quartz to produce these substances, which then decay after enough sediment covers the quartz.
Acheulean finds have been dated to 1.7 million years ago in Ethiopia. Less-advanced stone tools have been dated to as early as 2.5 million years ago in eastern Africa.
Over two days in 2005, Gibbon’s group identified 465 stone tools brought out of a diamond-mining pit bordering South Africa’s Vaal River, near the town of Windsorton. Those implements included 10 hand axes, two hand axes with large chopping edges known as cleavers and two elongated, three-sided tools called picks. The researchers have since recovered another 100 hand axes, 30 cleavers and 40 picks from the Windsorton pit. Sand and gravel from five diamond-mining pits provided samples for dating, says Gibbon, an archaeology graduate student at the University of the Witwatersrand in Johannesburg.
Findings at Windsorton, published online December 20 in the Journal of Human Evolution, raise the question of whether human ancestors developed Acheulean tools independently in southern and eastern Africa at around the same time, developed the tools in only one area from which the tool-making tradition spread rapidly to distant regions.
Gibbon suspects that Homo ergaster, a species regarded as a direct ancestor of modern humans, made the Windsorton hand axes. A nearby South African site has yielded H. ergaster fossils, but no fossils of any member of the human evolutionary family have been found in the Windsorton vicinity. Fossil finds have linked H. ergaster to Acheulean tools in eastern Africa.
Stanford University archaeologist Richard Klein suspects that Acheulean tool making originated in eastern Africa about 1.7 million years ago and reached northern parts of what’s now South Africa shortly afterward. “I doubt it arose more than once,” he says.
“East Africa has always been considered the place of origin of stone tools and subsequent technological developments, but I wouldn’t be surprised to discover that significant stone-tool advances took place in the Vaal River basin and then spread to the rest of Africa,” Gibbon says.
His team’s findings support a preliminary age estimate of 1.6 million years that other researchers have reported for Acheulean artifacts from South Africa’s Wonderwerk Cave, located about 100 kilometers northwest of Windsorton. Anthropologist Michael Chazan of the University of Toronto and his coworkers dated quartz grains from artifact-bearing soil and further verified the ages by identifying reversals of Earth’s magnetic field with known ages in the cave’s sediment. Their study appeared in the July Journal of Human Evolution.
Additional dating of Wonderwerk Cave deposits has confirmed that Acheulean activity there began 1.6 million years ago, with even older stone tools dating to 2 million years ago, Chazan says.
Still, the precise timing of Acheulean origins in eastern and southern Africa remains uncertain. “There could easily be a time lag between the two regions on the order of 100,000 years, in either direction, that we are not yet able to detect,” Chazan remarks.