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 Potosí, in what is now Bolivia—then the largest source of silver in the world. The Inca 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 The Ohio State University found it in 2003.