First published: 3 October 2007 (GMT+10)
Re-featured on homepage: 20 May 2021 (GMT+10)
In 2005 when British scientists reported the discovery of human footprints in a layer of volcanic ash in Mexico, it caused a sensation.1
That’s because they dated the footprints at 40,000 years old—a direct challenge to the ‘traditionally accepted’ view that humans only arrived in the Americas around 11,000 years ago.
However, subsequent paleomagnetic analysis and radioactive dating of the volcanic ash by American geologists put the date at 1.3 million years old.2
Director of the Berkeley Geochronology Center in California, Paul Renne said ‘You’re really left with two possibilities. One is that they are really old hominids—shockingly old—or they’re not footprints.’3
Renne suggests that the markings are impressions left by machines or animals that have passed through the quarry in recent times. Renne himself has seen vehicle tracks on the surface, and cows and other animals grazing nearby.
Interestingly, the British team documented over 250 footprints, most of which they claim are human. They also reported footprints of a dog, a cat and cloven hoofed animals.4 Some of the images that the team have published on their website look convincing as human footprints (figure 1 and 2), especially when they occur as a track of left-right steps (figure1) rather than isolated prints.
Geoarchaeologist Silvia Gonzalez, one of the British team who discovered the footprints, said they were in ash that was now as hard as concrete, and they had been uncovered without excavation. Previously quarry workers had removed up to 3m of lake sediment that had been deposited on top of the ash layer.
But there is one other possibility that Renne did not mention. It is possible that the date produced by his laboratory does not represent the true age.
In a nutshell, the dispute rides on the dating. Which date is correct—the British date or the American one?
Paleoanthropologist Tim White, professor of integrative biology at UC Berkeley, who knows Renne well, is standing behind the Berkeley date. ‘The evidence Paul has produced by dating basically means that this argument is over’, he stated.
Perhaps he was wondering how 40,000-year-old footprints would require a complete rethink of the timing, route and origin of the first colonization of the Americas. That would be quite a task for someone like White, who has been working in the field most of his professional life.
So White asserted that the issue is settled. But then he added, ‘Unless indisputable footprints can be found sealed within the ash.’
In other words, he will go with the Berkeley radiometric date—for the moment—unless human footprints can be proved, in which case he will discard the date.
Surely the dating game is not as fickle as that. Actually, the dating is a problem whether they are footprints or not.
It is not as if the British team pulled a date out of the air. They engaged the best laboratories in Britain and Australia, and used multiple dating methods on a range of different samples.5,6 Check this:
- Radiocarbon dating using Accelerator Mass Spectrometer on mollusc shells and organic balls by the Oxford Radiocarbon Accelerator Unit.
- Electron Spin Resonance dating on a mammoth molar by the Australian National University.
- Optically Stimulated Luminescence dating on sediments and ash by Oxford University.
- Argon-Argon dating on ash and lava by Open University.
- Uranium Series dating on animal bones by Bristol University.
Such an impressive list of tests would have cost a lot of money, and be surely enough to convince any sceptic. Who would possibly dispute that the 40,000 years date was soundly based?
None other than the head of the Berkeley Geochronology Center in California. Renne clearly does not trust the dating done by the British team.
Nor does the British team trust the Berkeley work. Silvia Gonzalez said that one possible reason for the large discrepancy in dating may be due to the mixed nature of the volcanic ash: ‘This ash has got a very particular mineralogy that is very difficult to date.’2
This simply illustrates that radiometric dating is not objective science. It is not like measuring the length of something, or its weight. Scientists don’t argue about the chemical composition of a rock, because measurements like that are objective, experimental science.
However, they do argue over calculated dates because every calculation is based on assumptions about the past, assumptions that cannot be checked because we do not have a time machine. And if the dates are unappealing then it is a simple matter to challenge the assumptions.
There is no objective tool that can measure age.
Like the head of the Berkeley Geochronology Center, creationist scientists are sceptical of radiometric dating too. We won’t accept any number that disagrees with the eyewitness, historical account of biblical history. You can’t get anything more reliable than that.
- McAloon, C., Footprints in Mexico create scientific stir, Associated Press, Live Science, 5 Jul 2005. Return to text.
- Controversial footprints, earliest man or modern machine, 25 Sep 2007. Return to text.
- Sanders, R., Alleged 40,000-year-old human footprints in Mexico much, much older than thought, University of California, Berkley, 30 November 2007. Return to text.
- González, S., Huddart, D., Bennett, M.R., González-Huesca, A., Human footprints in Central Mexico older than 40,000 years, Quaternary Science Reviews 25(3–4):201–222, section 2, 2006; Original site mexicanfootprints.co.uk no longer exists. Return to text.
- González, S., Huddart, D., Bennett, M.R., González-Huesca, A., Human footprints in Central Mexico older than 40,000 years, Quaternary Science Reviews 25(3–4):201–222, section 3, 2006; Original site mexicanfootprints.co.uk no longer exists. Return to text.
- González, S., Huddart, D., Bennett, M.R., González-Huesca, A., Human footprints in Central Mexico older than 40,000 years, Quaternary Science Reviews 25(3–4):201–222, section 4, 2006; Original site mexicanfootprints.co.uk no longer exists. Return to text.