The Hopewell culture was a large network of ancient Native American civilizations and settlements throughout eastern North America that came to an end around 500 CE – no one knows exactly why it happened.
But according to a new study published in the peer-reviewed academic journal Scientific Reports, the answer may be a comet exploding in the air.
What was the Hopewell culture?
Hopewell was essentially a dispersed network of settlements throughout eastern North America from around 100 BCE to 500 CE. It could be found as far north as Lake Ontario and as far south as parts of modern Florida.
These settlements were mainly on waterways and subsisted by raising crops and hunting, but also saw some sophistication in earthwork construction and the production of pottery and ornamental stone and metal.
The waterways were important, however, as they were the primary transportation routes for the Hopewell culture. This common network of trade routes is what is known as the Hopewell exchange system, and it was frequently used. Materials were traded between settlements, which then were turned into products to be traded further.
But then, it all suddenly ended.
Why did the Hopewell culture end?
This has been something many have debated over the years. A few reasons had been proposed, such as war or colder conditions. Some said the invention of the bow and arrow caused hunting to become more efficient and, consequently, lessen the amount of food available. Indeed, it would also have made warfare more dangerous, and a switch to larger settlements with walls and fortifications could have led to these changes.
But this new theory suggests that it was, in fact, a comet exploding in the air.
What is this comet?
At some point between approximately 252 CE and 383 CE, a comet impacted the Earth and exploded in the air.
There is evidence supporting this in several ways.
The University of Cincinnati researchers examined 11 different Hopewell sites in the Ohio River Valley, where they discovered a large amount of meteorite fragments – far more than what would be found in other time periods. These also included the presence of the rare metals platinum and iridium, which are often left behind in asteroid and comet impact events like this.
Not only that, but there was also the presence of a charcoal layer, which indicates that there was exposure to extreme heat.
BUT PHYSICAL evidence is just one thing: There is also oral evidence.
Although the Hopewell culture apparently died out, the people did not. Many Native American tribes descended from the Hopewells, and have passed down stories of this event that are all surprisingly simple.
“The Miami tell of a horned serpent that flew across the sky and dropped rocks onto the land before plummeting into the river. When you see a comet going through the air, it would look like a large snake,” explained UC anthropology professor Kenneth Tankersley, the study's lead author.
“The Shawnee refer to a ‘sky panther’ that had the power to tear down forests. The Ottawa talk of a day when the sun fell from the sky. And when a comet hits the thermosphere, it would have exploded like a nuclear bomb.”
These are just some of the descriptions, and they can easily be understood as referring to an impact event. In fact, as Tankersley noted, they seem similar to the witness descriptions given in the Tunguska event.
The Tunguska event was the last major asteroid impact incident to happen. Occurring in 1908 above the Podkamennaya Tunguska River in Russia, the asteroid in question was believed to have been as wide as 190 meters.
When the asteroid exploded in the air several kilometers above the area, it produced a massive 12 megaton explosion, causing widespread destruction for thousands of kilometers. That would make it about 800 times more powerful than "Little Boy," the approximately 15-kiloton atomic bomb detonated during World War II over Hiroshima, and 600 times more than "Fat Man," the 20-kiloton one detonated over Nagasaki three days later.
The death toll from the Tunguska event was extremely low, however, with only around three people thought to have been killed in it, due to how remote and sparsely populated the region was. But the damage was still evident, with about 80 million trees completely flattened by winds of around 27 km per second. Tremors and airwaves were even felt as far away as Washington and Indonesia.
The few eyewitness accounts that do exist recounted the terrifying explosion, strong winds and tremors.
"The sky split in two and fire appeared high and wide over the forest," recounted a man who was about 65 kilometers south of the explosion.
"The split in the sky grew larger, and the entire northern side was covered with fire," he said. "At that moment I became so hot that I couldn't bear it as if my shirt was on fire; from the northern side, where the fire was, came strong heat. I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, and I was thrown a few meters. I lost my senses for a moment, but then my wife ran out and led me to the house.
"After that such noise came, as if rocks were falling or cannons were firing; the Earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it," he said. "When the sky opened up, hot wind raced between the houses, like from cannons, which left traces in the ground like pathways, and it damaged some crops. Later we saw that many windows were shattered, and in the barn, a part of the iron lock snapped."
But is there other historical evidence for this aside from legends?
Yes, actually.
During this time period, accounts from astronomers in ancient China described 69 near-Earth comets.
So how did the comet destroy the civilization?
The destruction caused by this explosion would seem almost apocalyptic and would have absolutely devastated the landscape.
This, in turn, is exactly the problem.
Comets are, essentially, dirty snowballs made of cosmic dust, frozen gases and meteoroids. If one crashed into Earth's atmosphere, it would explode in what is known as an airburst and release what the study describes as a "devastating high-energy shockwave."
In the Tunguska event, this explosion caused the flattening of 80 million trees in the area.
But to a heavily agricultural society, this level of destruction would be absolutely catastrophic.
As an agricultural society, the resources the Hopewell culture settlements needed would have been destroyed by such an impact. They would lose the valuable food and supplies they need to survive the winter, for instance.
“When your corn crop fails, you can usually rely on a tree crop. But if they’re all destroyed, it would have been incredibly disruptive,” UC biologist and study co-author David Lentz said.
That this would cause a decline of and eventual end to Hopewell culture is, therefore, understandable.
There are some things the researchers still don't know, and more research needs to be done to better understand exactly what happened and how it impacted Hopewell.
But according to UC geology alumnus and study co-author Steven Meyers, the findings might lead to more interest in how cosmic events like asteroid and comet impacts helped shape the fates of prehistoric civilizations.
“Science is just a progress report: It’s not the end,” Meyers said. “We’re always somewhere in the middle. As time goes on, more things will be found.”