A contentious issue in the history of technology may have been settled by scientists from Germany and the UK who have demonstrated that pre-historic people may have invented metal smelting more than once. Researchers at Heidelberg University and in London and Cambridge suggest that what we today know as metallurgy may have had its origins in several distinct locations but all at about the same time, circa 8,500 years ago. The conclusion is based on an examination of the chemical components of copper slag and other copper artifacts from the Stone Age settlement of Çatalhöyük in the Near East.

We usually divide the history of civilization into the Stone, Bronze and Iron Ages. However, we were already materials scientists at the beginning of the Neolithic and processing copper metal some 10,000 years ago in the Fertile Crescent from the "Levant" through East Anatolia to the Zagros Mountains in Iran. Of course, this was humans using pure, native copper, rather than true metallurgy, says Ernst Pernicka, Scientific Director of the Heidelberg Curt Engelhorn Centre for Archaeometry in Mannheim. Copper is present naturally as both metal and ore and prehistoric humans perhaps saw it as a rather special stone. Conversely, the production of metal from ores ushered in new eras in our history so it is crucial to know when we began to convert material from the earth into this special stone through metal smelting.

A small quantity of copper slag from Çatalhöyük had until now been seen as the earliest evidence for pyrometallurgical extraction of copper from ore. The settlement existed from 7,100 to 6,000 BCE and is the most significant site in the Near East that offers us insights into the development of human habitats. The copper slag is present in layers circa 6,500 BCE and so pre-dates known copper smelting by approximately 1,500 years. "The find seemed to point to the birthplace of metallurgy, with the technology slowly spreading from there in all directions," explains Pernicka.

However, the new studies suggest that the slag may simply be a by-product of a domestic fire; crushed green or blue minerals were originally deposited in the burial and reduced during a post-depositional fire, the team reports. The extreme heat of the fire slagged the green copper ores, which were used as pigment. Indeed, this slag differs chemically from a bead of folded sheets made of pure copper from the Stone Age. This sheds new light on the Çatalhöyük copper slag and puts the earliest example of copper smelting to 5,000 BCE in Southeast Europe and Iran. The current findings hint at this development having taken place several times during pre-history. [M. Radivojevi? et al., J Archaeol Sci (2017); DOI: 10.1016/j.jas2017.07.001]

"Accepting multiple origins of metallurgy enables us to advance the focus of our research onto those parameters, which these progenitor cultures and metalliferous regions share, in order to identify the essential conditions leading to the invention and innovation of the controlled smelting of metal," the team concludes.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.