The Spanish conquest of the Incas is a sad chapter in history, one that has just gotten another gloomy footnote. By looking through the cores of ancient ice, scientists have determined that the first case of mass air pollution was caused by the silver mines of Spanish conquistadors.

After the fall of the Inca in 1532, levels of pollution spiked until the revolution in the 1800's. The mountaintop mines of Potosí in Bolivia were the world's richest silver source, and countless enslaved workers died removing it.

VOA News reports, "the sad conditions and fate of tens of thousands locals exploited in the silver mining operations during the colonial period," Ohio State University environmental scientist Paolo Gabrielli said, "Their work conditions must have been truly terrible. Many died because of the strenuous physical efforts but it was also not infrequent that underground mine galleries collapsed, burying and killing hundreds of people."

Though Silver was extracted by the Inca, it was primarily in open mines, removing veins high in silver content close to the surface. This all changed when the Spanish arrived and introduced a new refining proces that involved the pulverizing of silver ore into a powder, which released lead and metallic dust into the atmosphere. The powder was then mixed with mercury and heated, allowing the mercury to evaporate into the atmosphere.

The finings of the scientis were published in the "Proceedings of the National Academy of Sciences." In the report the scientists said they removed their core from the glacier at an altitude of about 18,000 feet.

The age of the ice was easily and accurately determined because there is a clear alteration between rainy and dusty seasons, making the ice show its age like rings on a tree. The samples were cut from ice that formed over 1,200 years ago.

Daily Mail reports that Dr Paolo Gabrielli said: 'This evidence supports the idea human impact on the environment was widespread even before the industrial revolution.'

Dr Gabrielli said: 'The fact we can detect pollution in ice from a pristine high altitude location is indicative of the continental significance of this deposition. Only a significant source of pollution could travel so far, and affect the chemistry of the snow on a remote place like Quelccaya.'