When and where did humans invent metal smelting? Scientists have found the answer to this long-debated question in the history of technology. Metallurgy does not have a single origin but probably arose at various locations at about the same time. The experts reached this conclusion after re-examining the 8,500-year-old copper slag and analysing the chemical composition of other copper artefacts from the Stone Age settlement of Çatalhöyük in the Near East.