About a billion years ago, North  America was facing imminent destruction.

Vast tectonic forces were threatening  to tear the continent apart, right through the middle. That didn’t end up happening, so we  still have a continent, which is cool.

But that time of looming apocalypse  did leave a lasting legacy which would not only shape the  geography of North America, but also the lives of its human inhabitants. So much so, that for a  time, around 9000 years ago, one Indigenous American culture used  the remnants of this geologic upheaval to become the most technologically  advanced in the world. To tell this incredible story, we’re going to hand this  episode over to our good friend, science communicator Alexis Dahl, who’s reporting from Michigan, the  one-time copper crucible of civilization. take it away Alexis [INTRO] Across the world and among different cultures,   human technology has followed  a pretty linear trajectory.

We started out in the stone age, shaping axes, spear- and arrow-heads out of stones like flint. Then, once we learned how to extract  metals from the rocks that contained them, we started casting those metals into more  effective tools, as well as protective armor. Civilization entered the bronze age.

Bronze is an alloy, which is a  metal mixed with another substance. It’s usually made from copper and tin, although  you could also swap the tin for arsenic. You shouldn’t, but you technically could.

This bronze alloy was the first  to be harnessed by early cultures. And there are lots of copper-bearing  rocks and minerals around. Green malachite, blue azurite and golden  chalcopyrite are all easy to spot, and are good sources of copper.

Tin is rarer, although it’s likely  that some of the first bronzes were accidentally created thanks to  tin contamination in these copper ores. And in some places, archeologists can identify a  transitional Copper Age or Chalcolithic, marking the very beginning of metalworking  alongside more dominant stone tools. Around the world, different cultures  figured out metalworking at different times, but the first metal tools typically date from 6  and a half to 5 and a half thousand years ago.

However, there is one unexpected  civilization that bucks this trend. In North America, archeologists have  found that copper was being turned   into tools some 9 and a half thousand years ago. That’s three thousand years before most other cultures  had metalworking figured out.

And we’re not talking about  just one or two pieces. Around Wisconsin and Michigan, tens of thousands of artifacts have been found   belonging to the creatively  named Old Copper Culture - an Indigenous American culture that thrived  around the Great Lakes for around 4000 years. Why did this group leap forward in technology while the rest of the world lagged behind?

The key lies in the geological events that laid  the foundations for the Great Lakes themselves, about 1 billion years ago. Around this time, North America was  located on a continent called Laurentia, which was at the center of an even  bigger supercontinent called Rodinia. Rodinia was still piecing itself together, and the eastern edge of Laurentia was colliding with another continent to begin  to form the Appalachian mountains.

However, in the middle of the continent,  the tectonic forces were reversed, as the flowing mantle pulled the two  halves of Laurentia apart from each other. The result was a huge rift in the crust, a lot like the East African Rift Valley today. Experts think that Africa will  be split into two continents with an ocean in between sometime  within the next 10 million years.

And that’s what Laurentia was facing too. As the crust was torn apart, lava  rose and flowed over the surface, and the existing rocks were fractured and filled with vast and complex hydrothermal  systems fed by magma down below. This so-called Midcontinent Rift System stretched for about 2000 kilometers  through central Laurentia, and if it had reached the continent’s edge would have eventually let in the sea and ripped  America’s West coast from the East, for good.

But for some reason, just as soon  as the rift got started, it stopped. Perhaps the pressure from the growing  Appalachian mountains was too great, or perhaps the tectonic forces  found an outlet somewhere else. But whatever the reason, America’s mid continent rift  system failed to reach the sea.

Instead, it left behind a U-shaped rift  valley that is now filled by Lake Superior, as well as a band of igneous  and hydrothermally altered rocks that stretch across the northern parts  of Minnesota, Wisconsin and Michigan. The volcanic fluids that penetrated these rocks carried and concentrated a bunch of  minerals and metals, including copper. The thing is, although copper can certainly  be found in the crust, it’s a reactive metal, so it'll typically combine with other compounds like sulfur, oxygen and carbonate if they’re around.

That’s how we get those copper-containing minerals like malachite, chalcopyrite, cuprite and azurite. So those were the raw materials  that most civilizations had to work with when they embarked  upon their metallurgy journey. But in the Mid-Continent Rift  System, things went differently.

Here, the hot, copper-containing volcanic liquids wound their way through thick  layers of volcanic rock, and there was nothing to react with that copper, leaving it all on its own. As the hydrothermal fluids cooled,  the copper solidified as pure, or native metal, like this. Because of the unique conditions  of the Mid-Continental Rift, this region has become home to the largest  deposit of native copper in the world.

It was so abundant, and so easy to find, that the first humans in the area  really couldn’t have missed it. And so, with pure, unadulterated copper   practically littering the  ground around Lake Superior, the people of the Old Copper Culture already had a head start on the  rest of the world’s metallurgists. But of course, not everyone  accepted this at face value.

Some of the early researchers who  found copper artifacts in this region straight up didn’t believe that Native Americans  could have produced them by themselves. They assumed that somehow Europeans had  crossed the Atlantic thousands of years ago, shaped the tools, and then exported  some of the copper back home. Okay...

But the timelines, as well as the  chemistry, reveal the true story. It’s likely that the Old Copper Culture   people first found the copper  nodules in glacial deposits, formed from the erosion of ancient rocks, because these soft, secondary deposits  are loose and easy to dig through. They later delved directly into  the source rocks themselves, with surface mining on Isle Royale and  around Copper Country here in Michigan.

The ancient humans turned the copper they  found into arrowheads and spearheads, as well as knives, axes, awls and fishhooks, through a combination of hammering,  grinding and molten casting. Researchers have used radioactive  isotopes to figure out just how old these copper artifacts are. Dating of the wood and rope  attached to spear points, as well as charcoal and bone found in Copper  Culture burial sites, reveals a surprising trend.

The Old Copper Culture is,  like, really really old. Isotopic evidence suggests that  members of the Old Copper Culture started extracting their metal  as far back as 9500 years ago. The oldest reliably dated artifact found to date  is an 8500 year-old spear point from Wisconsin, and much of the evidence clusters around  dates between 7000 and 5000 years ago.

Researchers think this corresponds to the  peak of the copper industry in this area. But then, something unexpected happened. Unlike other civilizations who made  the move from stone to metal tools, the Old Copper Culture didn’t  stick with their choice.

It seems that they all but abandoned copper  for practical objects by about 3000 years ago, opting instead to use the metal for  jewelry like beads and bracelets, while switching back to stone for their tools. Which sounds absolutely wild. If you have metal tools, in what universe do you go  back to the literal Stone Age?

Some researchers have suggested  that this unconventional shift came about as a result of social changes. Archeological evidence shows that  Old Copper Culture populations were becoming larger, with more social hierarchy. This would have increased the demand for  ornamental objects to reinforce that hierarchy.

Thus, more copper was needed to make  pretty things for Copper Culture elites, and less would have been available  to make boring things, like tools. But this might not have been the only reason. An experimental study in 2019 revealed  that, for all their apparent innovation, the Old Copper Cultures’s copper tools actually… weren’t all that great.

The scientists created their  own copper and stone arrowheads from the same stuff as the ancients used, and then used them on soft  plastic to simulate animal flesh. They found that the copper tools weren’t  any better than their stone equivalents, especially when considering the time  taken to make them in the first place. Stone arrowheads started out sharper, and after being used for the same amount of time, became no blunter than their copper cousins.

So maybe social demand for  pretty copper came into play, but it was only possible because the copper  tools weren’t great in the first place. But, why should this be the case  here in the New World North America and not elsewhere? The answer may lie in the extraordinary  purity of the copper in this area.

This incredibly pure copper may have  been something of a double-edged sword. These native copper nuggets were remarkable in  forming without any other elements mixed in, so those North American metalworkers  wouldn’t have needed to do anything other than heat them and reshape them. In contrast, other cultures  experimenting with copper would have had to smelt their metal away  from other compounds and impurities mixed in.

This would have been an imperfect  process, especially in primitive furnaces, so it's inevitable that some impurities  would have remained in the finished metal. And in the case of metals like copper, impurities tend to make a metal stronger. That’s basically the whole idea behind alloys.

You can imagine a pure metal as being made  of balls that are all the same size -- if you apply a force, layers of balls  can easily slide over one-another. But if you mix in other elements, it’s equivalent to throwing  in a handful of larger balls. They will catch and snag your sliding layers, making them less likely to move and  making the resultant metal more rigid.

Ultimately, that’s why the first really  successful metal age was the Bronze age, since the intentional alloying of  two softer metals -- copper and tin – made something that was much  stronger and more useful. But even before that, civilizations  were accidentally alloying their copper by not fully purifying it. However here, around Lake Superior,  the copper was already pure… and therefore soft.

Too soft, it seems, to survive in the long run. The remarkable copper nuggets  ended up being a curse in disguise. They may have been easy to find and  work, but they make terrible tools.

And there just wasn’t any motivating  force for the Old Copper culture to develop smelting technology  to move on to bronze. These people developed remarkable technology  in the context that they lived in. It’s not really their fault  that they hit a dead end.

Despite the eventual disappearance  of the Old Copper Culture, the legacy of these rare  metal deposits has lived on. Starting in the mid-1800s, a wave of  miners immigrated to Copper Country from places like England, Finland, and Canada, extracting millions of tons of metal in the  first mineral rush in United States history. And it's a heritage people  around here take very seriously.

I mean, we have Copper Island, Copper Harbor, and of course Copper Country as a whole. It’s a whole thing. And it’s all thanks to a fledgling rip in  the center of a billion-year old continent.

I’ve loved telling you about this  nugget of Michigan’s history. Savannah tell the people at home  how they can get some copper I will tell them. If you want to become a Rocks Box  subscriber or just learn more, you can head over to Scishow.rocks  or use the link in the description.

If you’re not into a monthly  shipment, don’t worry, we also have a selection of  specimens a la mine cart, too. Also, thanks to Alexis for showing  us around Michigan’s Copper Country. You can find her here on YouTube using  the other link in the description. [ OUTRO ]