Mankind Has Been Pumping Out Air Pollution for at Least 500 Years

It's easy to think of air pollution as a foible of modern society, but don't be too quick to consider our pre-industrial ancestors eco-friendly. It turns out humans probably started muddying the skies five hundred years ago.

That's according according to a new finding just published in the Proceedings of the National Academy of Sciences: The Spanish Empire can take credit for the most widespread pre-industrial air pollution in the Southern Hemisphere, which hails from Bolivian silver mines erected by conquistadors in the late 16th century. The discovery suggests that the hotly debated age of humans—the self-styled Anthropocene—may cut deeper into history than we realized.

"This evidence supports the idea that human impact on the environment was widespread even before the industrial revolution," study co-author Paolo Gabrielli of the Byrd Polar and Climate Research Center said in a statement.

During its conquest of South America, the Spanish Empire forced countless Incas to work in silver mines, located in the mountains of Potosí (in what is now Bolivia). While the Inca already knew how to refine silver, the introduction of new Spanish technology in 1572 boosted production many times over. Soon, the mines started belching plumes of lead dust into the air. For the first time ever, the taint of industry rose over the Andes.

Researchers first caught whiff of the dust in 2003, when excavating a section of the Quelccaya Ice Cap, located some 500 miles northwest of Potosí in Peru. Climatologists often refer to the ice, which formed over the course of 1,200 years as snowfall atop the Peruvian Andes was compressed and compacted, as the Rosetta Stone for Earth's climate history. Pockets of air trapped within the ice cores extracted there are like precious microcosms, each one a chemical record of natural—and anthropogenic—changes to our atmosphere.

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Researchers used mass spectrometry to measure concentrations of various chemicals in the ice, dating back to 800 AD. They were particularly interested in lead, since historical records described how the Spanish silver refining process involved grinding lead-rich ore into a fine powder. Sure enough, lead concentrations began spiking in the core at the very same time that records indicate silver mining took off. The researchers pegged Potosí as the source of the pollution by comparing the Quelccaya ice with peat bog cores from Tierra Del Fuego, sedimentary lake records, and other mines.

Several weeks ago, geologists proposed that the age of humans began in the mid 20th century, with radioactive fallout and the mass production and disposal of plastics serving as stratigraphic markers. Whether the news that we've been mucking up the skies far longer will sway the Anthropocene Working Group, which itself seems to assimilate new information at a geologic pace, remains to be seen.

"Our results indicate the difficulty in defining an unequivocal onset of the Anthropocene," Gabrielli told me in an email. "They suggest that this new epoch emerged discontinuously through space and time during human history."

However the Anthropocene ends up shaking out, Gabrielli's findings add to the growing litany ways humans of old transformed ecosystems. Indeed, we probably helped drive extinct a large chunk of Earth's megafauna—mammoths, giant wombats and the like—before the rise of agriculture. And the transition from hunting to homesteading wasn't so innocent, either: Farming probably began increasing greenhouse gas levels and impacting the Earth's climate eight thousand years ago.

We have, in other words, been messing with this planet since about the first time we set foot on it.

Update: This story has been updated to more accurately reflect the timeline and context of the air pollution record.