Rewriting the History of North American Colonization

Last week, we had a story about the Kennewick Man—9,000 year old human remains dating back to approximately 7,000 B.C. that were found in Washington State. These are the oldest identified human remains in North America.

But when is the oldest dated evidence of any human life in North America? Up until recently, it was thought that humans migrated from Asia over the Bering Strait land bridge and slowly travelled down through what is now Canada and into the United States. Anthropologists dated this migration following the end of the last Ice Age, in approximately 11,000 B.C. Before that time, the land bridge was covered in ice and would impossible to navigate. Only once the glaciers melted, would this have been possible.

However, a single previous study disputed this claim. Researchers sampled 92 skeletal remains of South American origin from approximately 500 to 8600 years ago, examining mitochondrial DNA to trace backwards through the matriarchal line. Their results, surprisingly, told the tale of a group of Siberian migrants who crossed the Bering Strait 23,000 years ago, much earlier than any previous interpretations. This group of approximately 10,000 individuals (including 2,000 child-bearing women) then hunkered down on the American continent side of the strait for over 6,000 years without moving. At this point in time, the North American continent was still a gigantic 3,000 mile ice sheet, utterly impassable on foot even with today’s technology, let alone with prehistoric skills and tools. These people, dubbed the ‘Clovis’ tribe, were only able to proceed as the ice sheets melted and receded. But from that small foothold on the continent, they spread through it and then down into South America. An alternate theory avoids the Bering Strait land bridge all together and instead suggests that early explorers made their way across the strait by boat to colonize the more temperate coastlines. One thing is a genetic certainty—by 12,000 B.C., mankind had settled the land from Alaska to Chile.

Enter a mastodon tusk discovered in the 1980s in Florida found at the bottom of a river in a location that was once a pond. It showed clear marks of man-made tools, suggesting that the mastodon had been felled and butchered by humans. However, when the tusk was carbon dated, the results suggested an age of approximately 14,400 years. But the study was discounted as being inaccurate since the accepted theory of migration at that time said the date was over 1,000 years too old to be possible.

Recently, researchers (including one of the original study scientists) returned to the ‘scene of the crime’ to re-examine the site of the tusk’s discovery, armed with today’s much more accurate technology and the knowledge that migrants were now proven to have been present in other areas of North America at the time. They believed the original data was correct and aimed to confirm it.

They entered the Aucilla River, excavating stratified layers of history, silt layered over centuries of sediment. And when they got down to the layer dating back 14,400 years, they found tools that could only have come from local tribes including a double-sided flint knife that would have been one of their most advanced tools. It’s also precisely the type of instrument that would have marked the mastodon tusk confirming the theory that not-only was the area inhabited 14,400 years ago, but that tribal members were killing and butchering prey with their early tools. The original study was correct after all.

Another interesting sidebar of this recalculation of migration pathways is the timing between human population and the large-scale disappearance of regional megafauna. Originally, it was believed the disappearance of mastodons, giant sloths, giant bison and others was tied to the arrival of mankind. But with this new timeline, it appears man and beasts co-existed for at least 1,500 years before the animals disappeared, likely hunted to extinction.

Photo credit: D. Laird