In ancient and medieval times, the chief source of lead came from melting galena, a lead-silver ore, to create silver coins. “When you try to extract silver, you additionally extract lead, something like 100,000 times as much lead as silver,” says McConnell. Then, from the beginning of the Industrial Revolution before the 1970s, lead entered the atmosphere primarily through fossil fuel burning; oil and coal contain the alloy. At every point in history, winds transported this contamination to the Arctic, where it settled, becoming encapsulated in ice with every snow.
But humanity’s once-prolific use of lead could really be a boon for historians. Lead pollution accumulated from Arctic ice cores can disclose, at year-to-year detail, the financial ups and downs of medieval Europe, as stated by the writers of a new study, published Monday in Proceedings of the National Academy of Sciences.
McConnell hopes his work will likely be of significance uncovering such historical information. “The concept is to provide a proxy or index of industrial output that historians will become very excited about.”
“[The study] largely confirms what we knew (or suspected) about silver production in the medieval and early modern periods, although at several points it appears to bring the historic record into sharper focus,” states Lawrin Armstrong, medieval economic historian at the University of Toronto. Buthe adds, he was surprised at the dramatic increase in lead pollution between 625 to 1000. “If this analysis is correct, silver coins (or ingots for the settlement of larger obligations ) played a more significant role in the ancient medieval market than I and most other financial historians imagine.”
From the early Middle Ages into the 1970s, lead pollution in the Arctic climbed between 250 and 300 times. About 1850, the pace at which that pollution was dumped jumped, representing all of the coal people started burning then. But direct contamination was increasing before then. “I’d always heard the Middle Ages was a flat period, not an economically vibrant period,” says McConnell. “[But] you notice very vigorous growth… especially between 500 AD and 1300.”
When a center of ice is drained from Arctic landscapes, it is basically a tree ring of atmospheric chemistry. So scientists can scrape the layers to reveal the past’s contamination. McConnell had been doing this for years, attempting to analyze the lead pollution impacts of the Industrial Revolution. But historians approached him about going back farther. Since direct contamination pre-1850 largely came from making those silver coins, the medievalists thought it could possibly serve as a quantitative measure of the economy way into yesteryear. (Formerly, they had been grain prices or relationship trees used in medieval construction, but”direct is a very objective record and a lot more complete,” says McConnell.)
“Lead is nice because the background levels are really low,” says Joe McConnell, a hydrologist at the Desert Research Institute and lead author of this new study. Even though volcanoes and desert dust naturally release some lead in the air, human actions are the source of the overwhelming bulk of direct that’s made its way to the sky.
For millennia, people were all-in on lead. It was used to brew wine, make silver coins, and to channel water in pipes. Even 50 decades ago, it was added to gasoline and included in house paint. Then, finally, authorities enacted stringent regulations to suppress the neurotoxic metal, where there is not any safe dose.
While direct pollution increases, normally, across the period that the scientists looked at, there are lots of ups and downs year-to-year or decade-to-decade. Lead pollution improved in time with known historical events, such as new mine discoveries, or if new technology debuted. And the metal decreased during times of famine, war, plague, or climate disruptions. During the Ice Age, which began around 1300 and introduced cold weather and crop failures, lead pollution plummeted. Emissions slowed much more throughout the Black Death, when a third of the European people died from the plague.
To create this particular record, McConnell and his team used 13 dated ice cores from Greenland and the Russian Arctic. The scientists also measured the direct concentrations from every and then used an atmospheric model to approximate the source of the pollution.