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.
Although the lead concentration in the core that Dr McConnell looked at shows many peaks and troughs, some overall patterns are clear. Emissions began to rise in around 1000BC. This corresponds to the spread of Phoenician traders and settlers from their home cities in the Levant into the western Mediterranean, and the consequent exploitation of galena mines in Iberia.
The rise and fall of Rome is also visible. An increase in lead concentration coincided with Rome’s victories in the Punic wars, against Carthage, the largest Phoenician colony, during in the third and second centuries BC. This was followed by a fall during the civil strife of the first century BC, a rise again when Augustus abolished the Republic and brought the pax Romana of the Empire, and another fall during the third century AD, when the state was engulfed once more by civil war, and also suffered invasion from the east.
The decline in lead pollution was enhanced by Rome’s switch from the silver denarius, which had been increasingly debased with copper, to a gold standard. Even allowing for that, though, the European dark ages, during which Spain was occupied by the Visigoths, are clearly visible in the record—as is the point when civilisation starts to return with the rise of the Frankish state that, under Charlemagne, became the “Holy Roman Empire”, and with the takeover of Spain by the Umayyad caliphate.