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180,000 years by the first ratio; 245,000 + 40,000 years by the second. And the El Horno dates were even "worse": greater than 165,000 years by one ratio; greater than 280,000 years by the second! Cynthia ignored these new dates, calling them "impossible".’ She considered the 22,000-year '*C date for Caulapan valid for her other Valsequillo sites as well—the only valid date." "Poor Barney!" the rest of us thought. "His methods only work on young material." PARADIGM SHIFT Although the evidence for very ancient hunters was clear, we other scientists on the project had our politically correct blinders on. Since the sites "couldn't be that old", we assumed out of hand that something was wrong with Barney's methods—until we began to look more closely at the sites, especially the Hueyatlaco site, and at our own lack of results. Hard to believe, but it took seven years of negative results at the microscope before my thinking began to change. What if Barney's dates were correct? If so, I would never find that elusive correlation I was looking for between a dated volcanic ash layer on La Malinche volcano and one of the undated ashes at the Hueyatlaco site. The matching layer I was seeking would, in real- ity, lie deeply buried in the flanks of the volcano, covered over with a quarter-million years' worth of younger deposits! As I began to look at the problem with new eyes, it was obvious that, geologically speaking, the Hueyatlaco site was old. The sed- iments were all highly weathered. The volcanic glass was turning to clay. There were many buried soils in the overlying sediment pile, each one representing hundreds if not thousands of years when the landscape just sat there with little deposition or erosion. The sediment cap over the artifact- bearing layers was at least 10 metres thick and probably had been much thicker at one time. Erosion by the near- by river had cut down through that cap at least 50 metres."! A quarter-million years? That meant that if we were ever going to date the site using other than the controversial uranium-series method, we would have to stop think- ing "New World" with its comfortable “C dates and start thinking "Africa". Only in Africa, with the early hominid Mandible (jawbone) from a mammoth skeleton research going on discovered by Armenta near the small hamlet of there. would we find renillas, north shore, Valsequillo Reservoir. ’ Protruding from the bone is a flint spearpoint. the means to date __ Inset: Another view of the spearpoint in place, such old archaeo- showing the damage it caused to the bone. logic material. (Photos from Armenta estate collection) JEALOUSY AND ACCUSATION Dating her sites was only one of Irwin-Williams' concerns dur- ing those years. She also had to contend with the insane jealousy of a highly placed archaeologist in Mexico City—a man who did all he could to discredit her, Armenta and their work. In a series of moves that sound like a plot for a TV soap opera, they were accused in print of incompetence, with dark suggestions of worse things.‘ Massive excavations were made by a rival team of archaeologists only metres from her trenches.* Armenta's life- work was confiscated and moved up to Mexico City,’ and he was forbidden by law to do any more fieldwork of any kind, ever. Cynthia easily refuted the charges against them,’ but it obvious- ly was a difficult time for her, for Juan, for us all. "IMPOSSIBLE" URANIUM-SERIES DATES Meanwhile, other scientists were also trying to date the site. In 1968 Barney Szabo, a geochemist with the United States Geological Survey (USGS), wanted to try the then-new radiomet- ric method on the fossilised bones—the uranium-series method. Cynthia sent Barney a molar from the butchered mastodon at El Horno, a pelvic bone from the butchered camel skeleton associat- ed with bifacial tools at Hueyatlaco, and a bone associated with the one stone-flake scraper that made up her "site" at Caulapan. (Caulapan had already been dated at approx. 22,000 years by the 4C method, using fossilised snail shells found next to the scraper.) The dates came back.’ Irwin-Williams was delighted with the ones for Caulapan: 22,000 + 2,000 years by one U-series ratio; 20,000 + 1,500 years by the other. They agreed closely with the “C date on the fossilised snail shells: 21,850 + 850 years. But oh, the other dates! The butchered camel pelvis from Hueyatlaco dated 10 times older than the oldest date we had ever considered: greater than NEXUS - 57 Mastodon phalange (toe bone) with deep cut encircling the base, found in the El Horno excavation. (Armenta, 1978, fig. 61-1) AUGUST - SEPTEMBER 1998