Ancient metal mines sullied global skies.

As Socrates took in the latest tragedy at his local theater, little did he realize that Athenian smelters were sending showers of fine metallic dust into the sky. Yet deep ice drilled from Greenland now provides clear evidence that a variety of heavy metals polluted the global atmosphere during ancient times-and in quantities far larger than expected.

Sungmin Hong of Domaine University in Saint Martin d'Heres, France, and his colleagues measured the copper concentrations in ice that dates back through the last 7,000 years to the beginning of the Bronze Age. As the Greenland glacial cap builds up year by year, each layer, like a ring of a tree, retains a chemical signature of the precipitation and dust that settle out of the atmosphere.

Unmistakable signs of copper emissions from smelting started showing up in Greenland around 2,500 years ago, during the Golden Age of Greece, the researchers report in the April 12 Science. Copper concentrations in the ice rose during the heyday of the Roman Empire, dropped during the Middle Ages, and then climbed again with the start of the Industrial Revolution. The researchers also compiled records of copper mining and smelting around Europe and Asia to estimate how emissions into the atmosphere changed with time. These data dovetail with the measurements made in Greenland, they report.

Although most people consider air pollution an invention of modern society, the new results "provide strong evidence that pollution was a global problem even in ancient times," comments Jerome O. Nriagu, an environmental geochemist at the University of Michigan in Ann Arbor.

In previous studies, Hong and his colleague Claude F. Boutron, as well as another team, had documented lead pollution reaching Greenland and northern Europe during Greek and Roman times (SN: 3/26/94, p. 198). But the copper results indicate that many by-products of smelting were wafting across the Northern Hemisphere and perhaps the globe.

In a preliminary analysis of Antarctic ice, Todd Hinkley of the U.S. Geological Survey in Denver and his colleagues found hints of air pollution from smelting going back as far as 4,000 years. Because Greenland lies closer to the location of these early societies, he suspects that Arctic ice will show clearer signs of the first widespread industrial activities. The health effects of these pollutants remain unclear. During Roman times, officials banned mining near some cities in Italy, perhaps because of the noxious vapors from smelting, which some Roman writers mentioned, says Nriagu.

As a result of inefficient techniques, early metallurgy emitted by-products in much higher concentrations than did practices adopted in the 19th century. Analysis of glacial ice can provide unique insight into how much metal the ancient world used, says Boutron. "Archaeologists have a lot of problems being quantitative for this early period. Here is a new, promising way to get quantitative data for archaeologists."