First steps into brave New World

One of the fossilised footprints discovered on the shoreline of Lake Valsequillo. Pictures / Liverpool John Moores University

LONDON - Humans "discovered" America 25,000 years earlier than previously thought.

Incontrovertible evidence announced yesterday, that mankind colonised the New World at least 40,000 years ago, will totally change key aspects of humanity's early migration story.

The new evidence - 269 human footprints preserved in ancient volcanic ash - has been discovered by Mexican and British archaeologists near the Mexican town of Puebla, 120km south-east of Mexico City.

The discovery is one of the most important archaeological finds of recent decades.

The layer of volcanic ash in which the footprints are preserved has been dated by two completely different dating techniques to between 38,000 and 39,000 years ago.

The fact that the two different dating techniques - radio carbon and OSL (optically stimulated luminescence) - have been used makes the dates extremely reliable.

Until now the earliest definite archaeological dates for a human presence in America is around 15,000 years ago in various parts of North and South America.

Because the newly discovered footprints prove that humans were in southern Mexico 38,000 to 39,000 years ago, and because human migration takes many centuries and even millennia to occur, it is virtually certain that humans arrived in America earlier than around 40,000 years ago.

The discovery also has immense implications for Asian pre-history. At present the earliest date for a human presence in the extreme east of Asia (eastern Siberia) is 35,000 years ago - but even that is 2000km west of where Asia used to connect with North America (what is now the Bering Straits).

When combined with existing knowledge of prehistoric climate, the new discovery suggests that humans may have entered the Americas during a slightly less cold phase - within the Ice Age - which occurred around 50,000 years ago.

They would either have walked over the ice-bound Bering Strait or island-hopped in primitive boats from East Asia to Alaska via the Kuril and Aleutian chains of islands, hundreds of kilometres south of the strait.

This would mean that the migration into the Americas occurred at about the same time as the normally accepted date of the early Aboriginal colonisation of Australia - and some archaeologists now believe that the first Americans were Australoid peoples closely related to the early Aborigines.

Given that the new evidence proves they were there about 40,000 years ago, it is also now conceivable for the first time that humans entered the Americas even earlier - perhaps during a much warmer spell (a true interglacial period) around 70,000 years ago.

The Mexican discovery means that archaeologists will now have to take more seriously two controversial and as yet unproven proposals: that a site in Brazil and another in Chile might date from 50,000 and 33,000 years ago respectively.

The Mexican footprints were made by at least four to six individuals (probably two adults and between two and four children) in at least three episodes, several weeks or even months apart.

In all three episodes, the adults and children were walking barefoot along the shoreline of a large lake (now a reservoir called Lake Valsequillo).

Each episode of footprints was sealed and therefore preserved by ash from successive eruptions of a nearby volcano, Mt Tolukuilla.

The humans were probably foraging for freshwater shellfish while the volcano was between eruptions.

The ash layer is between 2m and 4m thick, and the footprints have been found in the top 20cm, under 2m to 3m of lake sediments.

The discovery - announced in London - was made by archaeologists Dr Silvia Gonzalez and Professor Dave Huddart of Liverpool John Moores University and Professor Matthew Bennett of Bournemouth University.

"The discovery of the footprints in Mexico is, I believe, important because it shows that humanity's spread across the world was much faster than previously thought," said Gonzalez.

"What's more, this increased speed of migration shows that our ancestors adapted to new environments much quicker and more easily than we had imagined."

"The new discovery also gives additional support to the idea that the very early first Americans may well have been of Australoid type closely related to the Australian Aborigines."