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| replicas of copper arrowheads and knives crafted by people of North America's Old Copper Culture |
Copper’s allure has endured for millennia. Both ancient and modern mines for the extremely useful metal abound in North America’s Lake Superior region; long before modern miners extracted the ore from deep underground, local Indigenous communities dug it from shallow pit mines.
In fact, the south side of Lake Superior was home to 5,000 copper mines that date to at least 3,500 BCE. And, the extraction of copper yielded millions of pounds from that time period, yet only a very small portion of this copper can be found in Native American artifacts.
According to David Pompeani, a geologist at the University of Hawaii at Manoa, the age of these ancient mines had been a "long-standing enigma,” as earlier studies employed archaeological relics to determine when mine sites were active, but later mining at the same locations frequently destroyed the archaeological record.
In order to overcome this, he and his colleagues adopted a different strategy: rather than looking for artifacts, they searched for traces of mining that had been preserved in the environment.
So, the scientists looked to study sediments from two tiny inland lakes close to historic mines on the remote Isle Royale in Lake Superior, Michigan, for a new article in Anthropocene1.
Such sediments behave much like tree rings because they are impacted by annual fluctuations.
And, each layer represents a snapshot of the year as a whole, including weather-related incidents, wildfires, and pollutants.
Pollution from pre-industrial copper mining was mostly caused by lead impurities in copper deposits. Lead is a reliable substitute for recording human impact, as it is not a metal that is readily obtained naturally.
It took a lot of labor to harvest copper before sophisticated machinery.
First, Native Americans hammered it out of the rock, a laborious task that sent up dust and tiny shards of metal and stone.
Then, they most likely used bonfires to warm the rock, softening the copper and liquefying the lead that was simple to melt.
These fires vaporized the lead and spread it across the vicinity, dispersing particles over the ground and lakes.
The researchers discovered evidence of a lead pollution peak in lake sediments that occurred around 6,000 years ago during the Archaic period.
This corroborated archaeological data from the same time period and suggested a concurrent peak in large-scale copper mining.
The study demonstrates that the lead is a trustworthy conduit to understand copper mining.
Additionally, this validates some of the earliest-known large-scale mining operations in the globe and offers a fresh perspective on the functioning of Indigenous cultures.
There is a misconception that hunter-gatherers couldn't coordinate a mining operation. However, the lake sediment shows that they mined to the extent that it was visible in the environment throughout the Archaic era. Similar analyses of environmental pollution in small lakes could be utilized to look into global human implications.
Study:
Vall, K., Murphy, C., Pompeani, D. P., Steinman, B. A., Schreiner, K. M., Bain, D. J., DePasqual, S., & Wagner, Z. (2022). Ancient mining pollution in early to middle Holocene lake sediments from the Lake Superior region, USA. Anthropocene, 39(100348), 100348. https://doi.org/10.1016/j.ancene.2022.100348
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