The above is a fossilized human footprint found in Mexico. Researchers have dated it to 40,000 years ago. From Footprints rewrite history of first Americans
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.
The finds were dated by a variety of methods:
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, US.
Interesting stuff if the dates hold.
