The airburst

Many indigenous tribes of eastern and central North America have legends about a catastrophic explosion in mid-air in the distant past.

"The Miami tell of a horned serpent that flew across the sky and dropped rocks onto the land before plummeting into the river," said University of Cincinnati anthropologist Kenneth Tankersley, himself a member of the Piqua Tribe of Alabama.  "The Shawnee refer to a 'sky panther' that had the power to tear down a forest.  The Ottawa talk of a day when the Sun fell from the sky."

Tankersley led a team of researchers who believe they know why these legends exist.  Some time between 252 and 383 C.E., they say, a comet hit the upper atmosphere over eastern North America and exploded.  The impact rained micrometeorites over most of the continent -- and, they say, would have scorched an area the size of New Jersey.  The results would have looked like the aftermath of the Tunguska Event of June 1908, in which a similar airburst flattened an estimated eighty million trees in an area of over two thousand square kilometers.

The tipoff was similar to what the father-and-son team of Luis and Walter Alvarez found in the clay layer marking the Cretaceous-Tertiary boundary, and which caused them to suspect an asteroid collision as the cause of the Cretaceous Extinction: a layer of material that is high in two rare heavy metals, platinum and iridium.  Iridium, especially, is far more common in asteroids and comets than it is on Earth, and its presence in a dust layer is suspicious, to say the least.

The impact, Tankersley et al. theorize, is part of what led to the decline and eventual collapse of the Hopewell Culture, an interconnected network of tribes that extended from what are now Manitoba and Ontario all the way down to northern Florida.  They were characterized by a particular style of pottery, jewelry, and arrowheads, but even more by the distinctive mound-building that we still see traces of in Ohio, Indiana, and elsewhere.

An 1848 map of the Chillicothe Earthwork in Ohio [Image is in the Public Domain courtesy of the Smithsonian Institution]

Something, however, triggered this confederation of cultures to go into rapid decline.  By 500 C.E. mound-building had ceased completely, and there's evidence that the trade routes that linked the different member groups were no longer being used.  The constituent tribes themselves appeared to decrease dramatically, and it took centuries for the population to rebound.

The cause, say Tankersley et al., is an airburst -- which would have destroyed completely any communities within a hundred or so miles, but would have caused extensive damage much farther away, likely triggering crop failures.  Given the fact that in most pre-technological cultures, one bad harvest was all that it took to trigger famine and starvation, something like this would have been catastrophic.

It's fascinating that like the Cascadia rupture and subsequent tsunami that made its way into the legends of the indigenous people of the Pacific Northwest, an entirely different cataclysm seems to have been recorded in the oral histories of the people of central and eastern North America.  The day the sky exploded -- with the result that an entire civilization collapsed.

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