It’s the 16th century. The Spanish Empire’s conquest of South America is in full swing. During this time, thousands of Incas were forced to work the silver mines of Potosi (modern day Bolivia). At the time, these silver mines were the largest source of the precious metal in the world.

New technologies were being introduced by the Spanish Empire. This led to an incredible rise in silver production. And with it, thick clouds of pollution. Wind carried the pollution more than 500 miles northwest into Peru. That’s where researchers from Ohio State University found traces hundreds of years later. Specifically, the researchers found trace pollution in an ice core on the Quelccaya Ice Cap.

This ice core marks the first detailed record of widespread human produced air pollution in South America.

“This evidence supports the idea that human impact on the environment was widespread even before the industrial revolution,” said Paolo Gabrielli, study author and a research scientist at the Byrd Polar and Climate Research Center at Ohio State.

Lonnie Thompson, co-author of the study, described the ice core as “another keyhole into the past of human activity in that part of the world.”

A mass spectrometer was used on the ice core to see what types of chemicals were present dating back to 800 AD. Several chemicals were tested for including, antimony, arsenic and bismuth. But, it was lead that researchers were really looking for. There’s actually more lead in silver ore than silver.

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

What’s next for researchers? An ice core from the Dasuopu Glacier in southwest China. This ice core is the highest altitude ice core ever drilled and could tell us more about how our ancestors lived. About 8,000 years of climate history are packed in this ice core.

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