Source: (8-14-09)
Just as raising temperature can change the properties of iron and other metals, early humans heated stone to make it easier to flake.

The process transformed a stone called silcrete into an outstanding raw material for tool manufacture.

Doctoral student Kyle Brown, who led the research at the University of Cape Town in South Africa, said: "Our illumination of the heat treatment process shows that these early modern humans commanded fire in a nuanced and sophisticated manner.

"We show that early modern humans at 72,000 years ago, and perhaps as early as 164,000 years ago in coastal South Africa, were using carefully controlled hearths in a complex process to heat stone and change its properties, the process known as heat treatment."

Previously, the first use of heat treatment was thought to have been in Europe 25,000 years ago. The technique was not believed to have been invented until long after the ancestors of modern humans had left Africa and settled in Europe and Asia.