Humanity may only now be beginning to truly grasp the massive disease-causing, climate-altering effects of our air pollution, but the problem, new research finds, goes back a lot further than many have realized.

It turns out, say scientists writing in the Proceedings of the National Academy of the Sciences, that humans have been polluting the atmosphere at least as early as the 16th century, a good 200 years before the start of the Industrial Revolution. The credit goes to Spanish conquistadors, who developed mountaintop silver mines in present-day Bolivia and who, in 1572, developed a new technology that allowed them to up production, shooting plumes of lead dust into the air for what may have been the first time in human history.

(Oh, and just to pile on to a depressing bit of history, they did it by means of slave labor.)