It began long before industrial revolution.

• Position: Pollution - Silver refinery - Brief article

In the 16th century, during its conquest of South America, the Spanish empire forced countless Incas to work extracting silver from the mountaintop mines of Potosi--what now is Bolivia--then the largest source of silver in the world. The Incas already knew how to refine silver but, in 1572, the Spanish introduced a new technology that boosted production many times over and sent thick clouds of lead dust rising over the Andes for the first time in history.

Winds carried some of that pollution 500 miles northwest into Peru, where tiny remnants of it settled on the Quelccaya Ice Cap. There it stayed--buried under hundreds of years of snow and ice--until researchers from Ohio State University, Columbus, found it in 2003. They now report discovery of a layer within a Quelccaya ice core that dates to the Spanish conquest of the Incas, which contains bits of lead and bears the chemical signature of the silver mines of Potosi.

The core provides the first detailed record of widespread human-produced air...