Discovery of oldest footprints gives clues to Mexico's climate

Jan 02, 2014 by Harriet Jarlett
Discovery of oldest footprints gives clues to Mexico's climate
Tracks in situ.

The oldest human footprints in North America have been dated for the first time and could help scientists to understand what Mexico's climate was like 7000 years ago.

The new climate data, published in the Journal of Archaeological Science, comes from two sets of footprints found in the Chihuahuan desert in north-eastern Mexico.

The first of these sets was discovered in 1961 after workmen stumbled across them while building a road. At the time they were removed and placed in a museum where, despite being described in detail, their provenance was lost.

A team of researchers, from John Moores University in Liverpool, who were interested in where these prints came from began interviewing local people to see if they could find more. Eventually, in 2006, another track was found in a quarry.

'When we discovered these new prints, they were preserved in the same material as the ones in the museum. So we presumed it was a rediscovery of these lost footprints as opposed to a new discovery,' explains Dr Nick Felstead now of Durham University, lead researcher on the project.

To see if the two sets of prints were from the same track the teams needed to work out their age. So, they used oxygen and in the surrounding material to work out when our ancestors made the prints.

'The age of the prints in the museum had been given a best-guess at being around 10 to 15,000 years old, but they had never actually been dated,' says Felstead. 'The two sets of dates came back at 10.5 thousand years and seven thousand years old, so by age alone we knew they were separate; they couldn't have been same trackways.'

At 10.5 thousand years old, the museum footprints pre-date the oldest evidence of humans previously known in the area – a 9000 year old piece of human faeces.

Having dated the two sets of footprints the scientists decided to look at what the climate was like when these humans laid down these trackways.

The prints were preserved in sediments known as travertine – a mineral that precipitates out when water percolates through limestone rocks - so the scientists knew the area must have been far wetter than it is today. The water which formed the travertine also contains minute traces of uranium, and it was this that enabled the team to date the footprints. Over time uranium decays and turns into thorium, by measuring the ratio of uranium to thorium the scientists were able to determine how old the footprints were.

'It's in the middle of the Chihuahua desert, everyone always thinks that deserts are hot, arid and hostile but these show us that during the Holocene, the desert was just coming out of a period of glaciation and had only just started to dry out,' Felstead says. 'It's a window into a time when the desert was wet enough to support a much greater range of life.'

Explore further: Egypt archaeologists find ancient writer's tomb

More information: Journal of Archaeological Science DOI: 10.1016/j.jas.2013.11.010

Related Stories

Scientists discover first dinosaur trail in Victoria

Aug 10, 2011

Two sandstone blocks discovered by palaeontologists have provided the most extensive evidence of dinosaur footprints in Victoria. Found at Melanesia Beach, near Cape Otway, they represent 85 per cent of the ...

Thousands of dinosaur footprints uncovered in China

Feb 07, 2010

Archaeologists in China have uncovered more than 3,000 dinosaur footprints, state media reported, in an area said to be the world's largest grouping of fossilised bones belonging to the ancient animals.

Recommended for you

Egypt archaeologists find ancient writer's tomb

Apr 19, 2014

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Crowd-sourcing Britain's Bronze Age

Apr 17, 2014

A new joint project by the British Museum and the UCL Institute of Archaeology is seeking online contributions from members of the public to enhance a major British Bronze Age archive and artefact collection.

Roman dig 'transforms understanding' of ancient port

Apr 17, 2014

(Phys.org) —Researchers from the universities of Cambridge and Southampton have discovered a new section of the boundary wall of the ancient Roman port of Ostia, proving the city was much larger than previously ...

User comments : 0

More news stories

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.