Long before factories, electricity and cars, humans found ways to besmirch blue skies.
Deep layers of ice from high in the Andes chronicle air pollution in South America starting around 1540, some 240 years before the Industrial Revolution. The likely source of the smog was silver mining spurred by Spanish conquistadores, scientists report February 9 in the Proceedings of the National Academy of Sciences.
Previous lake sediment records from South America had hinted at the ancient adulteration but were murky on the timing. Glacial ice cores, on the other hand, offer a year-by-year record of air pollution fallout dating back centuries.
Researchers led by earth scientist Lonnie Thompson of Ohio State University cored the Quelccaya Ice Cap in Peru and tracked pollution back to A.D. 793. The researchers noted an uptick of toxic trace elements including lead, chromium and molybdenum after around 1540. Before then, the researchers found little sign of pollution and much of what they found could be attributed to windblown dust and volcanic eruptions.
The date of 1540 falls just after the Spanish conquest of the Inca Empire in 1532, during an upswing in silver production. The mining and metal smelting involved probably produced the smog, the researchers report. But they also note that colonial pollution pales in comparison to the smog of the 20th century.