GREENLAND’S icy mountains are not an obvious place to search for an archive of economic history, but a study just published in the Proceedings of the National Academy of Sciences shows that they provide one. Joseph McConnell of the Desert Research Institute, in Reno, Nevada, and his colleagues have tracked economic activity in Europe and the Mediterranean over the centuries by measuring variations in the amount of lead in a core of Greenlandic ice. Lead is a good proxy for economic activity because it is a by-product of silvermaking (lead and silver often occur in the same ore, known as galena), and therefore of the money supply. Extracting silver from galena involves boiling off the lead. Winds from Europe carried to Greenland enough lead pollution from this process for it to be preserved in the layers of snow that, compacted, form the island’s ice cap.