Human footprints rewrite history of the Americas

Kulapavana · July 8, 2005

Source: NewScientist.com news service

Published: July 5, 2005 Author: Robert Adler

Footprints rewrite history of first Americans

Human footprints discovered beside an ancient Mexican lake have been dated to 40,000 years ago. If the finding survives the controversy it is bound to stir up, it means that humans must have moved into the New World at least 30,000 years earlier than previously thought.

“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.

Sand and shells

But when were they made? It has taken the team two years, using a panoply of high-tech dating techniques, to determine that the prints are about 40,000 years old.

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.

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.

“Accurate and reproducible”

Gonzalez and her team expect the same. “This will be incredibly controversial, there’s 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 it’s accurate and reproducible,” Higham stresses.

How people got to Mexico 40 millennia ago is a matter for speculation. Bennett suspects that they migrated along the Pacific coasts of Asia and North America. But when it comes to the dates and footprints, he says, “those are not speculation at all".

The footprints remain where they were found. The team has used laser scans and rapid prototyping equipment to create highly accurate three-dimensional copies, accurate to a fraction of a millimetre, which can be viewed at the Royal Society's Summer Exhibition in London, UK, which ends on 7 July.

July 8, 2005

being rewritten (or should I say re-speculated). Just last week the material scientists got approval to study the 9,000 year-old bones of the "Kennewick Man" discovered in the mud of the Columbia River nine years ago:

<h3>Scientists finally study Kennewick Man</h3>

After a legal battle that lasted nearly eight years, scientists will finally get to study the ancient skeleton known as Kennewick Man.

The remains were found in July 1996 along the shores of the Columbia River in Washington State.

Estimated to be more than 9,000 years old, the Kennewick skeleton is one of the oldest, most complete specimens ever found in North America.

Eight anthropologists sued to study the bones after the US government seized them on behalf of Native American tribal groups, who claim Kennewick Man as an ancestor and want to rebury his skeleton.

Since early 2004, when the US Ninth Circuit Court of Appeals ruled in the anthropologists' favour, scientists have been negotiating with government agencies on a study protocol, said Paula Barran, a lawyer for the plaintiff scientists.

"We've been chomping at the bit to get this thing done," she said.

On Wednesday 6 July, a team of researchers will gather at the Burke Museum of Natural History and Culture in Seattle for a 10-day "measurement and observation trip".

The scientists want to figure out how chemical, biological and geological processes, as well as human actions, have altered Kennewick Man's skeleton since he died.

Finally getting to it

The scientists leading this week's study met briefly at the Burke Museum in December 2004 to examine the skeleton's condition and to outline an initial study plan, explained Thomas W Stafford Jr, a Colorado-based geochemist who will participate in the investigation.

First, a group led by Smithsonian Institution anthropologist Douglas Owsley will lay out the 300-plus bone fragments "so we can see the whole skeleton in anatomical correctness", Dr Stafford told the BBC News website.

Then, Dr Stafford's group will look for mineral stains and accumulation of sediment and calcium carbonate, which should tell them how the body was positioned in the ground.

"Was he a drowning victim, was he buried on purpose with arms folded in a certain way?" Dr Stafford said.

Scientists with other expertise will try to deduce Kennewick Man's cause of death, medical problems he had while alive and whether bone breakages happened during life or after death.

Throughout the process, Dr Stafford said, Dr Owsley's group "will do, from beginning to end, the definitive measurements and photographs".

Later analyses

Some of Dr Stafford's own work will wait until after Seattle. He will take with him a few remnants of bone that were used for radiocarbon dating several years ago.

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KENEWICK MAN: TIMELINE

7,200 BC - Kennewick Man lives and dies

28 July 1996 - Kennewick Man skeleton found in Columbia River

13 September 1996 - Kennewick bones granted to American Indians for reburial

17 October 1996 - Eight scientists begin legal battle to study Kennewick Man

4 February 2004 - Appeals court sides with scientists

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"I don't plan on taking any samples from the skeleton itself right now," he said.

Back in his lab, Dr Stafford will analyse the bones' protein composition, to see if there is enough for further radiocarbon dating to establish firmly Kennewick Man's true age.

"I may also be able to find that there's DNA preserved that hadn't been found before," he told BBC News.

A DNA sample would reveal which ancient and modern populations are most closely related to Kennewick Man, Dr Stafford added, but "if there's no DNA, then the fallback will have to be the physical measurements".

C Loring Brace, one of the plaintiffs and an anthropologist at the University of Michigan, US, thinks that the physical measurements will show that Kennewick Man was related to prehistoric inhabitants of Japan who may have migrated to the Americas separately from the people who gave rise to today's Pacific Northwest Indians.

But "just saying it is one thing," Dr Brace added. "I want to get my callipers on it, get the set of measurements, and run them through our database to see what they tell me."

The tribes who claimed Kennewick Man as an ancestor still do not want the remains studied, though.

"Our goal, our position has never changed," said Debra Croswell, a spokeswoman for the Confederated Tribes of the Umatilla Indian Reservation, one of the four tribes involved in the final court decision.

"We still want this individual reburied as soon as possible."

Dr Stafford does not agree: "If somebody else wants to look at it next week, next year, they should be able to come in just like we came in. This thing should be open. There should be no final opinion for maybe even years."