Scientists have debunked the claim that prehistoric peoples living in central Turkey 8,500 years ago invented copper smelting, putting an end to one fierce controversy.
It was known all along that the copper beads found in 8,500-year-old graves at the famous Late Neolithic site of Çatalhöyük were made by hammering native metal found in nature, not by smelting. But 15 bits of supposed "metallurgical slag", supposedly the "earliest evidence" for metal smelting in the world, are now shown to have been accidentally produced in a conflagration that half-melted green pigments that had been placed in a grave.
Smelting involves isolating metal from ore-bearing rock by intense heating. Professor Ernst Pernicka, of the University of Heidelberg, confirms that the native-copper beads found at Çatalhöyük and this "slag" were not chemically related.
That further supports the theory that the artifacts were made by manipulating local rocks and the "slag" wasn't from smelted copper ornaments put into the grave, but from copper-rich pigment that burned with the dead.
"Not every piece of semi-molten black and green stuff from an excavation is necessarily metallurgical slag. Yes, there are native copper beads in Çatalhöyük and no, they don't count as 'copper production' because they are just stones collected and hammered into shape, no melting involved!" Professor Thilo Rehren of the UCL Institute of Archaeology Rehren told Haaretz. "The native copper beads are part of a Neolithic (Stone Age) technology of collecting and hammering minerals and stones. And therefore they don't constitute metallurgy."
Fifty years ago, the analytical technology didn't exist to check whether these 15 semi-baked bits in an 8,500 year-old grave were made of native copper or the result of metallurgy, Rehren explains. Now such technology exists, enabling the re-assessment of the earlier assumptions, including by the same team seven years ago.
Burying the dead in the house
The metallurgists had realized all along that the handful of Çatalhöyük "slag" samples were only semi-baked. That indicated a non-intentional, accidental copper firing event. But the 'eureka' moment of how and why that happened arrived quite late, says Miljana Radivojevic of the University of Cambridge, lead author of the paper published this month in the Journal of Archaeological Science.
"When our pigment specialist (Duygu Camurcuoğlu of the British Museum) mentioned earlier examples of green and blue copper pigments in graves and our excavation specialist (Shahina Farid of the UCL Institute of Archaeology) reported firing events involving charred bones and materials in shallow graves, the penny started to drop," she told Haaretz.
"The people of Çatalhöyük had the habit of burying some of their dead within their houses, in shallow graves and even in benches around the inner walls. Some of these burials contained packs of green and blue pigment, crushed malachite, as Duygu Camurcuoglu, one of our co-authors has been able to demonstrate from some more recent finds from the site," Rehren told Haaretz.
For some long-lost reason, several of the houses in Çatalhöyük had been set ablaze in what seem to have been massive, intentional conflagrations. The "slag" was formed by incidental baking of green pigments that had been placed in the grave beneath the building, which was set on fire 8,500 years ago. The green pigments, not that the ancients necessarily realized it, were copper-rich.
As the blaze rose to 600 degrees and beyond, it reached as much as 90 centimeters into the soil and charred human bones buried under the floor of the house. It also half-melted pigment bits into metal – in other words, slag began to form, but only on the outside of these pigment pieces.
No metal was intentionally or otherwise produced and was certainly not made into jewelry or any other artifacts, say Rehren and Radivojevic.
So, the oldest known proven smelting remains are in Belovode, Serbia, from around 7,000 years ago, Radivojevic told Haaretz. There Radivojevic and the team did identify intentionally-produced copper slag, which has been analytically confirmed as the source for at least 16 heavy copper implements found across the Balkans.
In their elements
Prehistoric men were aware of at least seven elemental metals: gold, silver, copper, tin, lead, mercury, and iron, the last of which requires the highest smelting temperature. Of these, gold, silver and copper were mostly used in their "native" form.
The prehistoric smiths created decorative objects from native metal by intensive hammering combined with heating (or annealing), at temperatures no higher than those required for cooking, around 200 degrees.
All the copper objects found at Çatalhöyük dating to around 6,700 B.C.E. were made of native metal, meaning naturally-occurring rock rich in copper.
Native copper is bright red, like copper metal. Other forms of mineral copper, such as malachite, were also picked up for their aesthetic appeal for making jewelry, or used as a pigment. Indeed, to this day, in some areas of the Levant and Middle East, that greenish-blue hue remains popular, and is associated with good luck.
"We need to be clear," Radivojevic wrote to Haaretz. "There is no evidence for extractive copper metallurgy of any kind at the site of Çatalhöyük, and our research presents a definitive explanation how this contentious ‘slag’ had formed."
Generally, the excavations at Çatalhöyük, wihch began in 1958, have been very rich. It was a huge site in the Neolithic and Chalcolithic ages, but was abandoned some time in the Bronze Age. In 2012, it was declared a UNESCO heritage site. The numerous finds of the ancient settlement, which housed thousands of people at a time, include figurines that are preumably of deities, bull heads, an extraordinary mural that some people call "the earliest known map," and some of the oldest preserved textiles in the world. And beads.
Actually, most of the copper metal artifacts found at Çatalhöyük were beads of a type common in Anatolia going back almost 11,000 years. "Archaeologists unearthed many of these in other prehistoric Turkish, Iraqi and Iranian sites in the past century," Radivojevic says. These beads were all made of native, not smelted, copper."
"The invention of metallurgy is foundational for all modern cultures, and clearly happened repeatedly in different places across the globe," Rehren sums up. Some think copper smelting originated in what is today Iran, and spread through the region and to Europe. Copper artifacts have been found in the region that date to about 7,000 years of age.
A copper awl broadly dated from the Middle Chalcolithic period (5200-4600 B.C.E.) was found in a woman's grave at Tell Tsaf, in the Beit She’an Valley, in 2014, though precise dating is yet to be investigated.
Israel was evidently not the spot where smelting per se developed; however, the earliest examples of alloyed metal come from the Nahal Mishmar hoard, discovered in a cave near the Dead Sea and permanently displayed in the Israel Museum in Jerusalem. More than 400 objects, amongst which crowns and scepters, were made of then-unique alloys of copper with arsenic and antimony, and with a craftsmanship unparalleled at the time of production, almost 6,000 years ago.
Their color, however, remains until today the most spectacular display of aesthetical preferences of that period: besides bright red copper, it included silver (copper–arsenic) and purple (copper-antimony) objects, say Radivojevic and Rehren. Some of the metal for making these items probably originated in the Caucasus, more than 1,000 kilometers away. In other words, international trade was booming even then.
The million-shekel question remains whether smelting was discovered once and disseminated, or discovered multiple times. This paper has firmly promoted the latter.