Forbidden Archeology_ The Full Unabridged Edition - Michael A. Cremo [254]
A similar result was obtained when we reversed the order of the calculations. First we computed a uranium leaching factor using the ratio of thorium to uranium 234 and a sample age of 25,000 years. Using this uranium leaching factor, we then computed an age for sample MB3 based on the ratio of protactinium to uranium 235. This procedure yielded a date of 11,675 years rather than the expected 25,000 years.
Either way, these results are not consistent with the idea that the sample was deposited only 25,000 years ago, and that the leaching of uranium occurred fairly recently, at the end of the period of burial. According to our model, we should expect both sets of uranium series computations, done using the standard equations for radioactive decay, to yield results near 25,000 years. But they did not.
When we performed the computations assuming that leaching of uranium took place continuously rather than at the end of the period the bone sample was buried, similar results were obtained. In summary, the hypothesis that uranium leached out of the samples (either all at the end or continuously throughout the period of burial), and that the samples are therefore only 25,000 years old, is not consistent with the activity ratios reported for these samples.
At this point, one might raise the following objection. Admittedly, the date of 25,000 years suggested by Cynthia Irwin-Williams does not give good results in the above analysis. If we assume leaching of uranium 234 and uranium 235 took place, we would expect the computations for the thorium/uranium 234 and protactinium/uranium 235 ratios to yield the same results—25,000 years. But they did not. Then what about some other relatively young date? Could it be possible that using this alternative young date, good agreement might result?
We varied the assumed age for sample MB3, using the continuous leaching model, from 25,000 years through 250,000 years to see at what age the protactinium/uranium 235 age agreed best with the thorium/uranium 234 age. For assumed protactinium/uranium 235 ages from 25,000 up to 140,000 years the protactinium/uranium 235 ages disagreed with the thorium/uranium 234 ages by more than 30 percent. For a protactinium age of 180,000 years the thorium age disagreed by 20 percent, and the difference dropped as the assumed protactinium age increased. At 235,000 years the two differed by only .2 percent and at 245,000 years they differed by 3.1 percent. Thus the data reported by Szabo strongly support a date of around 235,000 years b.p. for the upper artifact-bearing layer (Unit C) at Hueyatlaco.
The same calculation was performed for sample MB8 using the continuous leaching model. The protactinium age was varied from 25,000 years through
370,000 years. We found that the thorium dates disagreed with the protactinium dates by more than 30 percent from 25,000 up to 260,000 years. At 300,000 years the two disagreed by 16 percent and this difference decreased to .32 percent at
355,000 years. Thus the activity ratios reported by Szabo strongly support an age of about 355,000 years for this sample from the site of El Horno, even if we assume, for the sake of argument, there was continuous leaching of uranium. Szabo pointed out that “sample MB8 was a tooth fragment from a butchered mastodon at El Horno, the oldest known site, and was therefore itself an artifact” (Szabo et al. 1969, p. 240).
Uranium series dating methods were also applied to bone samples from the nearby Caulapan site, yielding dates of about 20,000 years b.p. These agreed nicely with carbon 14 dates of 21,850 and 30,600 years from this site. We should note that the Caulapan carbon 14 date of 21,850 years applies to mollusk shells associated with the single artifact found at this site. Cynthia Irwin-Williams (1978, p. 22; 1981, p. 258) maintained that this was the only valid date for any Valsequillo artifact, and it should therefore be used for Hueyatlaco and El Horno as well. But the U.S. Geological Survey team could find no “geological basis by which the relation of the