Humans reached the Americas more than 15,000 years earlier than previously thought, according to research published today in Nature. But, the international team found, it was much later that the presence of humans affected now-extinct large animals.

Papers from researchers with the University of Oxford and the University of Zacatecas, Mexico, and a host of researchers from other universities, including in the UK the Universities of Exeter and Cambridge, provide important new insights into our understanding of the First Americans - and when they moved into the continent for the first time.

It was popularly believed people arrived in the Americas around 13,000 years ago but, this new research shows people entered the continent much earlier - over 30,000 years ago.

The Oxford team, including Professor Tom Higham and Dr Lorena Becerra-Valdivia used a powerful statistical approach to build a detailed chronological framework for the arrival and dispersal of humans into North America.

This showed that humans were likely present in the region before, during and after the Last Glacial Maximum (LGM). But more widespread occupation is likely to have begun much later, during a period of abrupt global climate warming between 14,700 and 12,900 years ago, when there was an increase in human occupation across North America.

According to Professor Higham, ‘A combination of new excavations and cutting-edge archaeological science is allowing us to uncover a new story of the colonisation of the Americas. The First Americans came from eastern Eurasia, and it looks as though there was a surprisingly-early movement of people into the continent.
‘The people that travelled into these new lands must have come by sea, because the northern parts of North America were impenetrable and sealed off from eastern Eurasia by a massive ice sheet until 13,000 years ago.
‘The discovery that people were here more than 30,000 years ago raises a range of key new questions about who these people were, how they lived, how widespread they were and, ultimately, what their fate was.’

When the timeline for humans was compared with dates obtained for extinct animals -including types of camels, horses and mammoths - the analysis showed human expansion, during this warmer period, happened at broadly the same time as their disappearance. The authors suggest that an increase in human population seems to be linked to a significant impact on the catastrophic decline of these large megafauna.

Dr Becerra-Valdivia says, ‘The results of this study allow us to understand the initial human occupation of the Americas in greater detail than ever before, and gives us the opportunity to harmonise new genetic, cultural and climatic evidence.
‘The peopling of the Americas was a complex and dynamic process and we need to combine insights from different disciplines to understand it fully. What is clear is that humans were present in the continent well before previously accepted dates. But it was only around 14,700 years ago that those people became more highly visible in the archaeological record, likely due to an increase in population.'

An international team of researchers working at Chiquihuite cave, in the Mexican state of Zacatecas, has found remarkable evidence of early occupation. Team leader Dr Ciprian Ardelean, from the University of Zacatecas and the University of Exeter, says, ‘The finds at Chiquihuite cave are extremely exciting. The archaeology is older than anything we have seen before and the stone tools are of a type that is unique in the Americas.
‘It is curious that the site was occupied so much earlier than others. It seems likely to us that the people of Chiquihuite represent a ‘failed colonisation’, one which may well have left no genetically detectable heritage in today’s First Americans’ populations.’

Head of the Oxford dating laboratory, Dr. Jean-Luc Schwenninger, who worked with the team, notes, ‘Our involvement in the dating of this extraordinary site stretches back almost ten years and, finally, to see the results published is immensely satisfying...the publication of these new discoveries and findings, which rock and challenge long established views, required extra amounts of diligence, scrutiny, patience and perseverance.’

The Last Glacial Maximum (LGM) occurred between 26,000 and 18,000 years ago. It is widely known as the peak of the Ice Age, during which global temperatures fell to their lowest for tens of thousands of years.

The two papers, entitled “The timing and impact of the earliest human arrivals in North America” and “Evidence of human occupation in Mexico around the Last Glacial Maximum” can be obtained from Nature’s press site.