Humans in America 130,000 years ago

Human settlement of North America may have occurred at least 115,000 years earlier than thought, if intriguing evidence unearthed in California is correct.

In a letter published in the journal Nature, a team of researchers led by Steven Holen from the Centre for American Paleolithic Research in South Dakota, USA, reports on the discovery and dating of broken bones found near San Diego 20 years ago.

The bones belonged to a mastodon (Mammut americanum) – an extinct mammal that looked somewhat like an elephant, or a mammoth – and showed clear marks of human butchery. The site where they were found also contained unambiguous human artifacts, namely hammerstones and anvils.

The artifacts, together with cut marks on the bones indicating they had been butchered while still fresh, led scientists to conclude that the massive animal had been sliced up to be eaten. However, at the time of the discovery dating methods were insufficiently precise to indicate the age of the remains.

Revisiting the finds, Holen and his team used a type of radiometric dating that relies on gauging the ratio of uranium to thorium in calcium carbonate material. The method is particularly accurate up to 500,000 years.

When applied to the mastodon bones, the results were unexpected, establishing that the animal died 130,000 years ago (give or take 10,000). This, in light of the strong evidence suggesting that the beast had met its demise – or at least been dismembered soon after death – by human hands, was stunning.

All other paleo-anthropological evidence available dates human arrival in the Americas to around 14,500 years ago, at the end of the Pleistocene period. If accurate, the new finding extends the time of settlement by an order of magnitude.

The evidence, however, does not establish that the ancient mastodon eaters were Homo sapiens. Indeed, it would be very unlikely that they were, given that our species is generally held to have migrated out of Africa only around 60,000 years ago.

Holen and colleagues state that their “findings confirm the presence of an unidentified species of Homo”.

The San Diego site, they add “is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of the arrival of Homo into the Americas”.

In an accompanying editorial in Nature, archaeologist Erella Hovers of the Hebrew University of Jerusalem in Israel says the evidence presented by Holen and colleagues has been rigorously researched.

However, she adds, “the proposed hominin narrative derived from these data has some gaping holes that need filling”.

She concludes: “Time will tell whether this evidence will bring a paradigm change in our understanding of processes of hominin dispersal and colonisation throughout the world, including in what now seems to be a not-so-new New World.”