There was a split; Bill Topping (I think that’s his name) first turned in the direction of an ET cause, but at some point (perhaps as the “new guy” added members to the team) parted company. :’) Not sure what you mean about 40K-50K too young for RC dates — the RC limit is around 50K, beyond which the level of 14C is too low. However, there were some 14C “spikes” which caused older stuff to appear younger, as the ratio was thrown off. That is discussed in the book. Other radiometric stuff is discussed as well. The earlier waves of bombardments are discussed quickly, but I suspect those will someday be fleshed out.
Redating North American sites
The 39,000 yr B.P. date proposed for the Gainey site is consistent with the prevailing opinion among many archaeologists about when the Americas were populated. It is also commensurate with dates for South American sites and with a Mousterian toolkit tradition that many see as the Paleoindian precursor. The proposed date for the Gainey site also falls closer in line with the radiocarbon date for a Lewisville, Texas, Paleoindian site of 26,610 ± 300 yr B.P.22,23 and radiocarbon dates as early as c. 20,000 yr B.P. for Meadowcroft Rockshelter.24 Since the Lewisville and Meadowcroft sites were likely exposed at the same time to thermal neutrons, we estimate that their dates should be reset to c. 55,000 yr B.P. and c. 45,000 yr B.P., respectively.
It is likely that Paleoindians occupied low latitudes during the full glacial and migrated to more northerly areas as the ice front retreated. Therefore the pattern of dates makes sense from the archaeologist's point of view. Dates for North American sites should generally be reset by up to 40,000 years, depending on latitude and overburden.
Geologists believe that before c. 15,000 yr B.P. the Wisconsinan glaciation covered the more northerly locations where Paleoindian sites have been found.25 The ice sheet would have shielded the landscape and any artifacts from an irradiation. (The Gainey thermoluminescence date of 12,400 yr B.P. is probably a result of the heat generated by the nuclear bombardment at that time, which would have reset the TL index to zero.) The modified dates for Paleoindian settlements suggest that the timetable for glacial advance sequences, strongly driven by conventional radiocarbon dates, should be revisited in light of the evidence presented here of much older occupations than previously thought."
THAT of course from 2001. I don't know if Topping and/or Firestone are still willing to defend his/their theory re the anomalous carbon dates, but some of that information has been included in the article at the head of this thread -- FWIW.