This New York Times article discusses a recent archaeological findings that suggests that early humans heat-treated their tools much earlier than once thought; a technique used to make tools harder and stronger. The new evidence suggests that heat-treating tools occured at least 72,000 years ago, quite a difference from the old estimate of 25,000 years. The archaeologists found no evidence of burning in the studied supporting their argument that the tools were intentionally heat-treated. In addition;
they conducted tests on some of the artifacts, including one that showed that flaked surfaces had a glossiness that occurs only when the stone has been heated, proving that the stones were heated first and then worked into tools.