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physical metallurgy 4e volume2
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Human ancestors have been using stone and other tools since long before the emergence of Homo sapiens approximately 200,000 years ago.[20] The earliest methods of stone tool making, known as the Oldowan "industry", date back to at least 2.3 million years ago,[21] with the earliest direct evidence of tool usage found in Ethiopia within the Great Rift Valley, dating back to 2.5 million years ago.[22] This era of stone tool use is called the Paleolithic, or "Old stone age", and spans all of human history up to the development of agriculture approximately 12,000 years ago | Robert w. Cahn and Peter Haasen t editors Fourth revised and enhanced edition Prof. Robert w. Cahn .