The wars that Carthaginians and Romans fought on Spanish soil between the 3rd and 2nd centuries before this era were recorded on ice. Greenland, more than 4,000 kilometers from the main battles, arrived (and arrives) small lead particles transported by the wind. A group of researchers has used variations in the concentration of this metal trapped in successive annual icy layers to detect the signal of the Punic wars. But also the black plague, the Industrial Revolution or the cars of the twentieth century. The whole history of Europe, especially the economic one, is written on ice.
For years, different scientific groups have been boring Antarctica, Greenland or any other large frozen mass to extract ice cylinders. With a logic similar to that of tree rings, these columns grow year by year with the depositions of water and snow. And mixed are also small organic particles, minerals or produced by humans and dragged there by the wind. These cylinders are not usually very wide, about five centimeters in diameter, but some have a depth of several kilometers (they are cut into sections). To determine its chronology, it is enough to find the signal of a volcanic eruption with a known date and they already have a precise time clock.
It is what a group of scientists has done, but not with one of these ice cylinders but with thirteen distributed between Greenland and the northern end of Russian Siberia. Separated some 2,200 kilometers from east to west and another 1,600 from north to south, it is the largest map of emissions trapped in the Arctic so far. The researchers focused on lead concentrations for two reasons. On the one hand, it is an element that is rarely found in the air in a natural way, so the possible variations would indicate some human activity. On the other hand, lead has been essential in economic history: it was present in Roman coins and has been key in the metallurgy of silver.
The highest concentration of lead in the ice of antiquity was during the 'Pax Romana'
"It's the first year-to-year record of Europe's industrial emissions over the past 1,500 years," says the director of the ice core laboratory at the Desert Research Institute in Nevada, and principal author of the article, Joe McConnell. . "Therefore, it provides new relevant information that allows historians to quantify how ancient and medieval societies responded to events such as epidemics, famines and wars," he adds.
The work, published in PNAS, begins in the 500 of our era and retakes the history where it had left another similar published last year that started 3,000 years ago with the emergence of Phoenician cities and its expansion throughout the Mediterranean. In the latter, the records in the ice, measured in nanograms (millionth part of a gram) per square meter and year, show a precise temporal evolution of the first Republic and then the Roman Empire. In the last republican years, the concentrations of lead declined while they multiplied by four in the first two imperial centuries, were the times of prosperity of the Pax Romana. "Since most of the emissions during these periods came from the mining and smelting of lead and silver ores (such as the galena argentifera), we can consider the emissions of lead as an indicator of global economic activity," McConnell said at the time.
The study just published begins to count on the Roman decline. Lead pollution trapped in the ice would not recover the levels of ancient Rome until well into the Middle Ages, in the time of Pepin the Brief and his successor, Charlemagne (eighth and ninth centuries) growing slowly until the thirteenth century. With the black plague of the following century, the concentration of the metal in the Arctic goes down halfway. In the middle of the 1500 it would lower another 25%. It is likely that here the importation of American silver by the Spaniards had something to do with it.
"It is very difficult for the South American pollution to cross the equator, so these emissions would not be seen in the Arctic," recalls the DRI's American researcher. In any case, he doubts that American silver will lower the European price and, therefore, reduce mining activity in Europe.
The presence of the metal in the ice multiplied up to 300 and did not go down until the approval of the first laws that protected the air quality
Splashed with contractions related to events such as cholera epidemics, the Napoleonic wars or the revolts that surrounded the bourgeois revolutions of 1848, the upward trend of pollution remained. Even after 1870, when the great countries abandoned the silver standard to move to the gold standard, the concentration of lead continued to rise. Although the contribution of silver metallurgy dropped, a new source came on the scene: the lead from the combustion of the car engine. From this time is also a marked translation of records. The ice cores located to the west trap more lead than the others. It coincides with the awakening of the US as an economic power.
"We have a global increase of between 250 and 300 times of lead pollution from the early Middle Ages to 1970," says DRI researcher and co-author of the study, Nathan Chellman, in a note. In this last year, the US government approved the US Clean Air Act, the first standard in the world that protected air quality. Since then, the amount of lead in the most recent layers of ice has been reduced by 80%, but it is still 60 times greater than in Roman times.
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