A new analysis of burned antelope bones from caves in Swartkrans, South Africa, confirms that Australopithecus robustus and Homo erectus built campfires roughly 1.5 million years ago—as many as a million years earlier than previously thought. The bones were first described in 1988 by paleontologist Bob Brain of the University of Cape Town. Brain suspected that they had been burned by humans because the degree of charring indicated temperatures of more than 1,100 degrees Fahrenheit, while natural grass fires on the savanna burn no hotter than 700 degrees. But Brain had no way to prove it.
Then Anne Skinner, a chemist at Williams College in Massachusetts, used a technique called electron spin resonance to examine the size of the free radicals left in the bones: The higher the temperature at which the bones were burned, the smaller the radicals would be. Not all the antelope bones had been burned to ...
