THE mystery over when humans first populated the Americas continues to deepen. The latest date for rocks near Puebla, Mexico, which were said to bear fossilised human footprints, contradicts the suggestion made in July that humans reached the Americas 40,000 years ago. If people had indeed arrived this early then we would have to rethink everything we know about the history of early human migration.
Silvia Gonzalez of Liverpool John Moores University, UK, surprised the world鈥檚 media in July at a Royal Society exhibition in London by suggesting that markings found in a layer of ancient volcanic ash near Puebla were 40,000-year-old footprints. This would mean that people arrived in the Americas at least 30,000 years earlier than previously thought (快猫短视频, 9 July 2005, p 19).
But the markings are unlikely to have been made by humans after all, because new argon dating reveals the rocks are 1.3 million years old. The first humans did not evolve in Africa until a million years later (Nature, DOI: 10.1038/nature04425).
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Paul Renne of the University of California, Berkeley, who led the new dating study, says that he is surprised the markings were considered to be human footprints. 鈥淭he prospect of making such an exciting discovery can colour one鈥檚 judgement,鈥� he says. Renne also says that when Gonzalez announced her findings, her team had argon-dating results consistent with a 1-million-year age for the marks, but had dismissed them because of a large margin of error.
When contacted by 快猫短视频, Gonzalez said she would prefer to reply formally to Renne鈥檚 Nature paper rather than comment now. She plans to publish her team鈥檚 results in a peer-reviewed journal in January. 鈥淚t is indeed surprising that Nature is publishing this before our own formal publication, but such is science these days,鈥� she says.
