Near-Earth comet explosion may have triggered end of Native American Hopewell culture

Hopewell archaeological sites stretching across the Ohio River Valley were exposed to fires and extreme heat.

The reason for the rapid decline of the Native American Hopewell culture around 1,600 years ago has puzzled archaeologists for over a century. Now, researchers have uncovered evidence that falling debris from a near-Earth comet created a colossal explosion over North America, devastating Hopewell villages and the surrounding landscape.

Dr Kenneth Tankersley, anthropology professor at the University of Cincinnati, uses a magnet to demonstrate how micrometeorites collected across Hopewell sites contain metals such as iron. Photo: Michael Miller.

According to a study, published in the Nature journal Scientific Reports, researchers from the University of Cincinnati (UC) conducted investigations at eleven Hopewell archaeological sites stretching across the Ohio River Valley. The team found an unusually high concentration and diversity of meteorites, including micrometeorites and pallasites (stony meteorites).

Dr Kenneth Tankersley, UC professor of anthropology and the study’s leader author, said: ‘These micrometeorites have a chemical fingerprint. Cosmic events like asteroids and comet airbursts leave behind high quantities of a rare element known as platinum. The problem is platinum also occurs in volcanic eruptions. So we also look for another rare element found in non-terrestrial events such as meteorite impact craters — iridium. And we found a spike in both, iridium and platinum.’

Sampling of habitation surfaces at all eleven sites revealed a layer of charcoal, suggesting a total area of 9,200 square miles were exposed to fire and extreme heat.

Radiocarbon and typological dating analysis established that the event took place between AD 252 and 383, a period when 69 near-Earth comets were observed and recorded by Chinese astronomers.

‘What’s fascinating is that many different tribes have similar stories of the event,’ said Dr Tankersley.

Through their oral histories, various Algonquin and Iroquoian tribes, descendants of the Hopewell, speak of a calamity that struck the earth.

University of Cincinnati anthropology student Louis Herzner, bottom, and anthropology professor Kenneth Tankersley use a scanning electron microscope to study iron and silicon-rich microspherules collected at ancient Hopewell sites. Photo: Larry Sandman.

‘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,’ continues Dr Tankersley.

Further cultural evidence is presented by a comet-shaped mound constructed at a Hopewell site called the Milford Earthworks – the epicentre of the cosmic explosion – as well as discoveries of jewellery and pan flute instruments interred in burials, that had been crafted from metal forged from fallen meteorites.

According to David Lentz, UC biology professor and co-author of the study, the raining debris and extensive fires would have been ‘very injurious to agriculture’.

‘People didn’t have good ways to store corn for a long period of time. Losing a crop or two would have caused widespread suffering.’

Walnut and hickory trees – good winter food sources – would also have disappeared.

The research team is currently studying pollen trapped within sedimentary layers from the Ohio River Valley in order to uncover more about the ecological impact of the airburst.

They hope this research will lead to greater interest in how cosmic events affected prehistoric human societies.