We tend to associate industrial pollution with the modern era, but human civilizations have been contaminating the planet for thousands of years. By drilling deep into Greenland's ice sheet, an interdisciplinary team of researchers has chronicled the industrial waste produced by the ancient Greeks and Romans over a 1,900-year period, linking pollution to economic booms, wars, and even plagues.
An indelible aspect of the ancient Greek and Roman economies involved the mining and smelting of lead and silver ores. The resulting emissions drifted up into the atmosphere, travelled thousands of miles, and eventually settled onto Greenland's frozen surface. In a cyclical process that lasted for centuries, snow and ice covered this lead pollution, creating numerous sedimentary layers, and by consequence, a geological record extending for hundreds of feet into the ice.
Armed with the assumption that these layers of lead could be read like a history book, archaeologists, economists, and historians from the Desert Research Institute (DRI), the University of Oxford, and other institutions, analysed a 423.67m-long (423 meters) ice sample taken from the North Greenland Ice Core Project (NGRIP). The resulting analysis, published yesterday in Proceedings of the National Academy of Sciences, shows that ice cores can be used to estimate the amount of pollution produced by ancient civilizations, and by consequence, infer levels of ancient economic productivity. Likewise, the researchers were able to match the ebbs and flows of industrial pollution to known historical events, such as imperial expansion, wars, and plagues.
Analysing an ice core.Photo: PNAS
For the study, the researchers counted the ice layers like the rings of a tree, creating an annualized chronological account of pollution trapped within Greenland's ice sheet. More than 21,000 measurements of lead and other chemicals were done to build an accurate and continuous, 1,900-year-long record of the ancient pollution. Simulations of atmospheric transport were also used to match the sediments found in the ice core to their likely place of origin.
The record starts around 1100 BC during the late Iron Age, extends through Antiquity and late Antiquity, and finally ends in the early European Middle Ages around 800 AD. This roughly coincides with the rise and fall of the Greek and Roman civilizations.
Continuous ice core analysis.Image: PNAS
"Because most of the emissions during these periods resulted from mining and smelting of lead-silver ores, lead emissions can be seen as a proxy or indicator of overall economic activity," explained Joe McConnell, lead author of the new study and professor of hydrology at DRI, in a statement.
Armed with this continuous, high-resolution record of lead pollution, the researchers looked for links to significant historical events. As the new study shows, pollution rates began to rise around 900 BC, a time when the Phoenicians, an ancient East Mediterranean civilisation, were expanding their trading routes into the Western Mediterranean. Soon after, the Carthaginians and Romans increased their mining activities, particularly in the Iberian Peninsula - a development that jibes well with the Greenland ice core data. Emissions dropped noticeably during the last eight decades of the Roman Republic (509 BC to 27 BC), a tumultuous political period known as the Crisis Years. The highest levels of sustained lead pollution coincided with the height of the Roman Empire - the Pax Romana economic and cultural boom that lasted from the the 1st to 2nd century AD.
"The nearly four-fold higher lead emissions during the first two centuries of the Roman Empire compared to the last decades of the Roman Republic indicate substantial economic growth under Imperial rule," said coauthor Andrew Wilson, a professor of the archaeology of the Roman Empire at Oxford University.
In addition to matching the waxing and waning of lead pollution with wars, imperial expansion, and political instability, the researchers were also able to link falling pollution rates with plague, including the the Antonine Plague, which lasted from 165 AD to 180 AD. "The high lead emissions of the Pax Romana ended exactly at that time and didn't recover until the early Middle Ages more than 500 years later," explained Wilson.
Not surprisingly, this study involved a diverse team of specialists, including archaeologists, ice-core specialists, atmospheric scientists, and economic historians. Interdisciplinary research is on full display here, providing a fascinating study as a result.