Traces of copper at what was thought to be the birthplace of metallurgy turn out to have been made by accident. The finding overturns long-held ideas about where and how metallurgy was invented.

Archaeologists have been divided on metallurgy's origin for decades. Did it emerge many times over in different parts of the world? Or did it start in just one place, from which it spread throughout the world?

Many adherents to the latter theory believed that the 8,500-year-old burial site of Çatalhöyük in central Turkey was the most likely candidate for a single origin of metallurgy. There are distinctive traces of fired copper at the site, which have been taken to be slag, a by-product of smelting, for more than 40 years.

But reanalysis of the copper remains suggest that they were burnt accidentally, not in a systematic attempt to make solid metal from ore, finds a study in the Journal of Archaeological Science. The copper was contained in the grave in the form of a green dye, not as a pure metal or alloy.

"From the beginning of our study it was clear that the small handful of 'slag' samples were only semi-baked," said study author Miljana Radivojevic of the McDonald Institute for Archaeological Research at the University of Cambridge.

"This indicated a non-intentional, or accidental copper-firing event, but the 'eureka' moment of how and why that happened arrived quite late."

The scientists found evidence of charring in the grave, suggesting that the copper substance was not slag after all, but burnt dye.

Thilo Rehren of the UCL Institute of Archaeology, also a study author, said: "The invention of metallurgy is foundational for all modern cultures, and clearly happened repeatedly in different places across the globe.

"As we have seen, not every piece of semi-molten black and green stuff from an excavation is necessarily metallurgical slag."

The results put to rest the claim that Çatalhöyük was the sole origin of metallurgy, the authors say, instead arguing it had many independent origins in civilisations across the world.