Historical copper trapped in ice
Historical copper trapped in ice
February 8, 2017 by Jan Berndorff
View of the Nevado Illimani glacier in Bolivia from La Paz. Credit: Paul Scherrer Institute/Theo Jenk
South America's mining industry supplies half the world with copper. The world's largest mines are located in the Andes. Yet just when copper production began there has remained unclear, until now. Very few artefacts from the early high cultures in Peru, Chile, and Bolivia have been preserved. Now, however, researchers of the Paul Scherrer Institute PSI in Villigen, Switzerland, are on the trail of this mystery. Through analysis of ice from the Illimani glacier in the Bolivian Andes, they found out that by around 700 BC, copper was already being mined and smelted in South America. Their findings are published in Scientific Reports, an online journal of the Nature Publishing Group.
In South America, copper has been mined and smelted for around 2700 years. This has now been determined by researchers of the Laboratory of Environmental Chemistry at the Paul Scherrer Institute PSI in Villigen, Switzerland, through analyses of glacier ice from Bolivia. Copper mining in South America has enormous importance: Chile and Peru are the two largest copper producers in the world; Chile alone accounts for more than 30 percent of global copper production. Yet the beginnings of this essential industrial sector have remained obscure. The only certain evidence came from the time of the Moche culture, which flourished on the northern coast of Peru between 200 and 800 AD. Numerous copper objects from this culture, such as jewelry and ritual tools, have been found. From earlier times, however, there are few finds and no written records.
The ice of a glacier is, in principle, a kind of archive; in its layers, as in the growth rings of a tree, records of the region's climate development and air quality are stored away. Each year, a new layer of frozen precipitation is deposited on top. And every time, dust particles that were floating in the air at the time are embedded in the new layer. After drilling deep into the glacier and extracting a long column of ice, scientists can bring it—with great care and under refrigeration—into a laboratory for analysis. In just this way the team of Anja Eichler, the study's first author, and project leader Margit Schwikowski took a 139 m-long ice core that had been drilled during a 1999 expedition, at an altitude of around 6,300 m on the Illimani glacier in Bolivia, and analysed the deposits of metallic dust in particular.
The PSI researchers Anja Eichler (left) and Margit Schwikowski, two authors of the study, in the cold room, where the ice core from Illimani was cut. Credit: Paul Scherrer Institute/Markus Fischer
In a cold room of the PSI, the researchers continuously melted the ice core layer by layer, with a device they had developed themselves, and analysed the meltwater with a mass spectrometer. This instrument can separate different chemical elements from each other and determine their respective mass. Thus we worked our way back in time to roughly 4500 BC— the ice corresponding to this time was at a depth of around 134 m, Anja Eichler reports. And we determined that the first elevated copper concentrations that must trace back to human activity occurred around 700 BC. Living to the northwest of the glacier at that time were people of the Chavin culture, the first civilisation in the Peruvian Andes, while the Chiripa culture, a relatively simple society, lived in the immediate vicinity of Lake Titicaca. This is known from archaeological excavations. Hence it is possible that both practiced copper metallurgy, smelting copper ore to obtain pure copper for the production of artefacts. Copper particles emitted during this process made their way, on the wind, up to the glacier and were deposited there in the corresponding ice layers, says Margit Schwikowski. These particles added to the natural copper from mineral dust and thus produced the particularly high copper concentrations.
Read more at: https://phys.org/news/2017-02-historical-copper-ice.html#jCp
Science:
http://www.democraticunderground.com/122850626