Year after year, the economic history of the Roman Empire seems as impossible to reconstruct as the lost books of Livy Rom. But something close to such a record has now been retrieved from the most unlikely places – a glacier in central Greenland.
The recording is not written in Latin but on lead. The lead emissions generated by mining in northern Europe reached Greenland and were washed down during snowfall. The snow gathered to ice and kept a record dating back thousands of years.
Ice cores from Greenland have long been used to track global climate change, which is recorded in the oxygen isotopes of frozen water. The project to measure old lead emissions in ice cores was initiated by Andrew I. Wilson, an Oxford University archaeologist who researches the Roman economy. A French team tried this in the 1
Deep Greenland ice cores are hard to come by, as it can take three or four years to drill down to the bedrock. But Dr. McConnell knew of a core that had to be abandoned when the drill got stuck at the 6,500-foot level. Nevertheless, the core recorded 40,000 years of annual snowfall, and the Danish Keeper of the Core left Dr. Kirk. McConnell's lab used a section of about 1,400 feet from its upper parts dating back to 1235 BC. Correspond to. around 1257 AD
In the laboratory, the ice core was cut into bars that were just over three feet long and stood on a heating pad and were melted from below. Grooves in the pad deflected water from the central and purest part of the core to instruments known as mass spectrometers, which measured the amount of lead continuously at one-hundredth of a picogram, which is one trillionth of a gram. When the ice core melted at a rate of two inches per minute, Dr. McConnell's team found that they were able to perform 12 measurements per year during Roman times.
The dates of these ice years were verified by synchronizing with other chronologies such as those derived from tree rings and volcanic eruptions.
The continuous record of lead pollution is not as good as the figures for the Roman gross domestic product, which nobody knows, but it seems to reflect the general economic health of the Roman state.
The results, published in the Monday edition of the Proceedings of the National Academy of Sciences, show a wavering line whose peaks and valleys correspond to significant events in Roman history. The lead emissions rose in times of peace and prosperity, such as the Pax Romana, the 27 BC. It lasted until 180 AD and fell in the civil wars before the Pax and the rise of Emperor Augustus. There were also dramatic drops that coincided with the Antoninus plague of 165-180 AD, which was considered smallpox, and the Cypriot plague, which was uncertain, became lead from 250 to 270 AD
In Roman economy often used water pipes and sheathing hulls of boats. His production was also representative of a central economic activity, the use of silver in the Roman silver coin, the denarius. Silver occurs in lead ores, and the process of separating silver from lead at high temperatures has been a major source of lead in the air. In the early Roman Empire, the denarius was 100 percent silver. But under Emperor Nero, from 64 AD, the share of silver was reduced to 80 percent, and the state made a decent profit by recycling the pure silver denars into degenerate ones.
These changes coincided and may have been caused by a decline in silver production and such a decline in lead emissions is registered shortly after 60 AD in the ice core of Greenland. Under the Emperor Trajan, there was a brief return from 103 to 107 AD to make silver coins. The historical event is also reflected in a short increase in lead pollution, which ends in AD 107
Lead emissions reflected in the ice core fell from 235 to 284 AD during the Imperial Crisis, when the Empire almost collapsed under the pressure of internal discord, barbarian invasions and the Cypriot plague. Thereafter, the economy rebounded a bit as measured by lead, but entered a final phase of decline caused by the retreat of Roman legions from Britain in the early 5th century AD and the collapse of the Western Roman Empire in 476 Historians have been trying to reconstruct the gross domestic product of the Roman Empire, but have to make too many assumptions, Dr. Wilson. "I would not say that the lead pollution scale is a close representation of GDP, but it is probably the best overall health economic representative we have."
He and Dr. McConnell is now working to see if lead isotopes (lead atoms of different weights) in the ice core will help identify the geographic sources of lead production, taking into account the fact that nearby lead sources, such as the United Kingdom, would have contributed more to Greenland pollution removed like the Rio Tinto mines in Spain.