Human activity, from burning fossil fuels and fireplaces to the contaminated dust produced by mining, alters Earth's atmosphere in countless ways. Records of these impacts over time are preserved in everlasting polar ice that serves as a sort of time capsule, allowing scientists and historians to link Earth's history with that of human societies. In a new study, ice cores from Antartica show that lead and other toxic heavy metals linked to mining activities polluted the Southern Hemisphere as early as the 13th century.