Footprints of 'first Americans'

[Troubleshooter]

http://news.bbc.co.uk/2/hi/science/nature/4650307.stm

Human settlers made it to the Americas 30,000 years earlier than previously thought, according to new evidence.

A team of scientists came to this controversial conclusion by dating human footprints preserved by volcanic ash in an abandoned quarry in Mexico.

They say the first Americans may have arrived by sea, rather than by foot.

...snip...

The team used several methods to date a variety of material from the site near Puebla, Mexico, in order to be sure they were right about the age.

"We have materials that have been dated below the footprint layer, the footprint layer itself and on top of the footprint layer. Everything is making sense," said Dr Gonzalez.

The researchers used radiocarbon dating on shells and animal bones in the sequences and dated mammoth teeth by a technique called electron spin resonance. The sediments themselves were dated by optically stimulated luminescence.

...more...