If true, this would completely change our view of how and when the Americas were first colonised, says Chris Stringer, head of human origins at the Natural History Museum in London, UK. But like several US experts, he is reserving judgement until the dates can be independently confirmed.

The discovery was made by an international team led by Silvia Gonzalez, a geoarchaeologist at Liverpool John Moores University in the UK. She found the fossilised footprints in 2003 in a quarry near the city of Puebla, 100 kilometres southeast of Mexico City. I walked 1 metre and started to see them, Gonzalez says. It felt like a thunderbolt.

In just two days, Gonzalez and her colleagues found hundreds of human and animal footprints preserved in a layer of ash from a nearby volcano. The footprints were made along the shore of a lake and were submerged after the water level rose, preserving them under sediments.

They are unmistakably human footprints, says team member Matthew Bennett at Bournemouth University in the UK. They meet all the criteria that were set up after the Laetoli prints were found [in Tanzania in 1976]. The sizes suggests that about one-third of them were made by children.

The earlier dates have been heavily criticised, but this study has used several state of the art techniques to produce this one date:

The key date came from shells in the lake sediments, which the team carbon-dated to 38,000 years ago. Sand grains baked into the ash and dated using optically stimulated luminescence corroborated the finding.

The researchers also used argon-argon, uranium series and electron spin resonance techniques to date the layers. The footprints are clearly older than 38,000 years, says team member Tom Higham of the carbon-dating lab at the University of Oxford, UK.

The conventional view is that humans arrived in the Americas via Beringia around 11,000 years ago, when a land bridge became available between Siberia and Alaska. There have been claims about earlier waves of settlers, who must have made the crossing over water, based mainly on sites with signs of habitation dated up to 40,000 years ago, but these claims have drawn intense criticism.

Gonzalez and her team expect the same. This will be incredibly controversial, theres no doubt about that, Higham says. They invite other researchers to scrutinise their findings, due to be published in the journal Quaternary Science Review.

We have done a year of solid work to make sure its accurate and reproducible, Higham stresses.

eScottie

Minneapolis, MN

August 2003

JUL 05, 2005 05:56 AM

nah...it was aliens. there was another one a few yards away pointing and saying "ha! look what you stepped in, quebak! stupid martian!"

[Edited on Jul 05, 2005 5:56AM]

SurfBetty

Atlantic Beach, FL

December 2003

JUL 05, 2005 06:05 AM

cool...I love stuff like this.

Science makes me happy.

frankjohnson

I'm lost

November 2004

JUL 05, 2005 06:32 AM

Hopefully now the 40,000 yr old group will be taken seriously.

comicking

Rosemount, MN

May 2004

JUL 05, 2005 06:33 AM

I'm confused. The first link takes me to a KBP Google search which resulted in several chess references. The 2nd link talks about the theories. Where is the article from?

It sounds interesting though.