Americas’ ancients march back in time

Who were in fact, the first humans to reach the Americas, when did they get there and what did they find?

The dangers of sea level change are very much in the news at present, so it is a salutary lesson that 15,000 years ago, so much polar ice was locked up that the sea was about 120m lower than at present. Humans could walk across what is now the English Channel, and you could hike from New Guinea to Tasmania without crossing salt water. However, the Bering Strait was covered with ice, presenting a barrier to human movement between Siberia and Alaska.

What the DNA tells us is that all native Americans are related to East Asians. Archaeologically, we also know that Bluefish Caves in Central Alaska were sporadically visited and stone tools have been found there in association with the bones of reindeer, mammoth and horses with cut marks from butchering. Radiocarbon dates reveal settlement as early as 24,000 BP (before present).

One model for the early settlement of North America has it that the mammoth hunters of Beringia were isolated there until the climatic warming that set in from 15-14,000 BP opened two routes south between the ice sheets. Once they were safely south of the ice, there was a very rapid migration indeed. This was a time of surging population growth in environments that must have appeared familiar to the mammoth hunters of Beringia. Paisley Caves, in Oregon, dates to about 14,300 BP, and human faeces have revealed a diet of fish, water birds, bison and extinct camels and horses. At Hebior, in Wisconsin, in a spruce-dominated tundra setting, a mammoth had been trapped in the edge of a lake and dispatched with stone spears before being butchered.

Those first American hunters migrated down the west coast to reach Monte Verde in southern Chile by 15,000 BP, where wooden foundations of huts had walls covered in animal hides. Their footprints have survived and the hunters’ diet included extinct llamas and elephants along with lumps of chewed seaweed.

Archaeology is known for its surprises. The early settlement of the Americas was, it seemed, pinned down to about 15,000 years ago until excavations took place at Chiquihuite Cave in Mexico. Hundreds of stone tools in layers 3m thick have recently been dated to 33,000 BP. That early, the crossing into Alaska would have been boggy but possible, and travel south might well have involved boats along a coastal route. And why not? Humans crossed into Australia across an impressive stretch of ocean at least 17,000 years earlier than that.