"Scientists can finally track [ancient Rome's] economic booms and recessions—thanks to the exhaust of its massive coin-making operation, preserved for centuries in Greenland’s ice sheet"

TA:

Why does the amount of lead in the atmosphere tell us something about the Roman economy? “It’s a proxy for coin production. That’s the biggest thing,” said Seth Bernard, a professor of ancient history at the University of Toronto. When the Roman government needed to pay for something, it ordered the creation of new silver coins. These coins were produced, in part, in mines on the Iberian peninsula. But these mines didn’t excavate pure silver: Instead, they unearthed an ore of silver, lead, and copper that had to be smelted into silver. This process filled the air with lead pollution.

Once in the air, these lead emissions did not stay in one place. Instead, it wafted with the winds, eventually blowing into squalls and storms over Greenland. When these storms deposited lead-tainted snow or sleet over the Arctic island, the precipitation fused with the ice sheet and became its newest layer.

...

When compared with other studies, research suggests that Western Europe may have seen higher lead emissions during the Pax Romana than at any time prior to the Industrial Revolution, nearly 1,800 years later.

This finding reverses a widely cited study from the 1990s that reached almost exactly the opposite finding.