Playing footsie with the evidence? -- On the Mexican "footprints"

[Jacques Cinq-Mars]

All,

Instead of the promised (HERE) formal response to the Renne & al.’s paper (HERE), it appears that Sylvia Gonzalez et al. have chosen to maintain the “Mexican footprints” debate at a BBC level of scientific discourse:

'Footprints' debate to run and run

By Martin Redfern
BBC NEWS - Published: 2006/01/16 18:55:52 GMT


It was a sensational discovery - human footprints said to be 40,000 years old, preserved by volcanic ash in an abandoned quarry in Mexico.

The announcement, in July last year, created a flurry of excitement, but was then promptly dismissed by a second team of researchers who re-dated the rocks at 1.3 million years old, impossibly ancient to bear human traces.

The original claim has not gone away, however.

The first widespread evidence for the human occupation of North America came from the town of Clovis in New Mexico.

The beautiful fluted stone-spearpoints made by the Clovis people are found on many sites and date back 11,500 years or so. They are believed to have been left by people who crossed a land bridge that once existed between Siberia and Alaska.

But there is an increasing body of evidence for earlier occupation of the Americas, dating back to a time when the overland route through the ice would have been impossible.

'Car park'

The best evidence probably comes from Monte Verde in Chile and dates back at least 12,500 years. But to have reached so far south by then, people must have entered the continent earlier still.

There have been many claims of earlier dates, but few have been substantiated. So the announcement of 40,000-year-old footprints from Mexico was greeted with scepticism and caution.

It came from a team led by Silvia Gonzalez, a Mexican working at Liverpool's John Moores University.

You can certainly read on HERE, but please, don’t give too much attention to the BBC’s overview of very early New World prehistory. Nor should you expect too much, I suppose, from the promised on site assessment by the BBC Radio 4 team. Who are these people?

Also, you should have a look at John Hawks’take on this non-news (HERE). I particularly like the respect he has for geochronologists.

Jacques

[Daryl Habel]

All,

Instead of the promised (HERE) formal response to the Renne & al.’s paper (HERE), it appears that Sylvia Gonzalez et al. have chosen to maintain the “Mexican footprints” debate at a BBC level of scientific discourse:

'Footprints' debate to run and run
By Martin Redfern
BBC NEWS - Published: 2006/01/16 18:55:52 GMT
It was a sensational discovery - human footprints said to be 40,000 years old, preserved by volcanic ash in an abandoned quarry in Mexico......
(SNIP)

You can certainly read on HERE, but please, don’t give too much attention to the BBC’s overview of very early New World prehistory. Nor should you expect too much, I suppose, from the promised on site assessment by the BBC Radio 4 team. Who are these people?

Also, you should have a look at John Hawks’take on this non-news (HERE). I particularly like the respect he has for geochronologists.

Jacques

The promised Quaternary Science Reviews article documenting the 40,000-year-old "footprints" in Mexico has been published in this month's issue:

Quaternary Science Reviews
Volume 25, Issues 3-4 , February 2006, Pages 201-222

Human footprints in Central Mexico older than 40,000 years

Silvia González, David Huddart, Matthew R. Bennett and Alberto González-Huesca

Abstract
The timing, route and origin of the first colonization to the Americas remains one of the most contentious topics in human evolution. A number of migration routes have been suggested and there are different views as to the antiquity of the earliest human occupation. Some believe that settlement happened as early as 30 ka BP, but most of the currently accepted early sites in North America date to the latest Pleistocene, related to the expansion of the Clovis culture, while the oldest directly radiocarbon dated human remains are 11.5 ka BP. In this context new evidence is presented in this paper, in the form of human footprints preserved in indurated volcanic ash, to suggest that Central Mexico was inhabited as early as over 40 ka BP.

Human and animal footprints have been found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in the Valsequillo Basin, south of Puebla, Mexico. This ash layer was produced by a subaqueous monogenetic volcano erupting within a palaeo-lake, dammed by lava within the Valsequillo Basin during the Pleistocene. The footprints were formed during low stands in lake level along the former shorelines and indicate the presence of humans, deer, canids, big felids, and probably camels and bovids. The footprints were buried by ash and lake sediments as lake levels rose and transgressed across the site. The ash has been dated to at least 40 ka BP by OSL dating of incorporated, baked lake sediments.

For access to the abstract and article:CLICK HERE.
I haven't read it yet, so I don't have any idea whether the article addresses the questions raised by the Renne et al. paper.
Dar

[SteveF]

They do briefly address Renne et al at the end.  They argue that the footprints are footprints, note the absence of sedimentological support for Renne and go on to admit that the dating methods used by both teams appear accurate (though they cast some doubt upon the palaeomag - clearly the most significant of the Renne arguments they need to attack) and therefore further work is required to solve this dilemma.  They have a major grant to do so. 

Jim Rose has an editorial on the subject that is well worth reading.

I have some thoughts on my new, embryonic, blog:

http://pleistoceneperson.blogspot.com/