A closer look

You might think human-caused atmospheric ruin started with the Industrial Revolution, but the Romans beat us to it by two millennia. Deep within the Greenland ice sheet, scientists unearthing stratified layers of frozen snow found highly toxic spikes of trapped lead aerosols. These poisonous chemical signatures perfectly match the massive, open-air silver smelting operations of the Roman Empire, proving their insatiable greed was quite literally altering global air quality.