for National Geographic News
In July a team of English researchers reported the discovery of human footprints in Mexico that appeared to be 30,000 years older than when most scientists believe humans arrived in the Americas.
Researchers commonly accept that humans came to the Americas some 11,500 years ago. But new dating of the Mexican find suggests that the features are in fact 1.3 million years old.
If the new dates are correct, the footprints could be among the most incredible hominid traces ever discoveredor, more likely, not footprints at all.
"One-point-three million years is a lot older than I expected," said Paul Renne, director of the Berkeley Geochronology Center at University of California, Berkeley.
"I repeated the experiment nine times using different samples, usually single chunks of this basaltic rock, and they all gave the same unambiguous results."
Silvia Gonzalez, a geoarchaeologist at England's Liverpool John Moores University, and a team of colleagues first discovered the features in 2003. The researchers found them embedded in basaltic lava on the floor of an abandoned quarry near Puebla in central Mexico.
The team identified the indentations as footprints and dated them at 40,000 years old.
But if Renne's new dates are correct, the prints may be those of an incredibly ancient hominid, made well over a million years before the Americas are believed to have been inhabited.
Or they may simply be indentations in the rock.
Renne reports his new dating results in this week's Nature.
The First American?
Renne visited the site in June 2004 and noted that it shows the effects of many impacts over time.
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