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November 30, 2005

Be Even More Cautious About 1.3 Million Year Old "Footprints" from Mexico

Perhaps you remember the supposed 40,000-Year-Old "Footprints" found in Mexico that I wrote about back in July. Well, perhaps not. At that time, I said, we need to be cautious. In fact, my post was titled, "Be Cautious about the 40,000-Year-Old 'Footprints' for Mexico." Now there is a new press release from the University of California, Berkley that raises even more questions.

Alleged footprints of early Americans found in volcanic rock in Mexico are either extremely old - more than 1 million years older than other evidence of human presence in the Western Hemisphere - or not footprints at all, according to a new analysis published this week in Nature. The study was conducted by geologists at the Berkeley Geochronology Center and the University of California, Berkeley, as part of an investigative team of geologists and anthropologists from the United States and Mexico.

[snip]

. . . Paul Renne, director of the Berkeley Geochronology Center and an adjunct professor of earth and planetary science at UC Berkeley, and his colleagues in Mexico and at Texas A&M University report in the Dec. 1 issue of Nature a new age for the rock: about 1.3 million years.

"You're really only left with two possibilities," Renne said. "One is that they are really old hominids - shockingly old - or they're not footprints."

My bet is that they are not footprints.

The news release also has the following observation,

If the depressions were footprints, they could not have been made by modern humans, he noted, since even in Africa, Homo sapiens did not appear until about 160,000 years ago. Given the age of the volcanic rock and lacking other evidence of early human ancestors in the Americas 1.3 million years ago, the researchers wrote in their paper, "we consider such a possibility to be extremely remote."

Renne used the argon/argon dating technique. And there are other problems besides the date,

Many rocks retain evidence of their orientation at the moment they cool in the form of iron oxide grains magnetized in a direction parallel to the Earth's magnetic field at the time of cooling. Because the Earth's field has repeatedly flipped throughout the planet's history, it is possible to date rock based on its magnetic polarity.

Feinberg [a UC Berkeley graduate student] found that the rock grains in the volcanic ash had polarity opposite to the Earth's polarity today. Since the last magnetic pole reversal was 790,000 years ago, the rock must be at least that age. Because the Earth's magnetic polarity changes, on average, every 250,000 years, the argon/argon date is consistent with a time between 1.07 and 1.77 million years ago when the Earth's polarity was opposite to that of today.

Moreover, Feinberg found that each individual grain in the rock is magnetized in the same direction, meaning that the rock has not been broken up and reformed since it was deposited. This makes extremely unlikely the possibility that the original ash had been weathered into sand that early humans walked through before the sand was welded into rock again.

"Imagine two-millimeter-wide BBs cemented together where they're touching," Feinberg said. "The paleomagnetic data tell us that these things did not move around at all since they were deposited. They haven't been eroded and redeposited anywhere else. They fell while they were still hot, which raises the question of the validity of the footprints. If they were hot, why would anybody be walking on them?"

When Abnormal Interest calls for caution, one should be cautious.

Update December 1, 2005

afarensis has an update that gives the proponents response to Renne's team's work.

Posted by Duane Smith at November 30, 2005 9:06 PM | Read more on Paleoanthropology |

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Comments

Rats, you beat me to it...

Posted by: afarensis at December 1, 2005 3:58 PM

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