CompuServe Messages

Hi, Jon– I would expect _slightly_ older datings from the outer edges of an igneous intrusion than in the center, but not because of some isotopic fractionation. The outer regions should generally be the first to cool and solidify, being exposed to a nice heat sink in the form of surrounding rocks. Are these people claiming greater radiodate differences than this? One method of separating heavy water from water is to distill it (keeping only the last water to condense) over and over and over and over… ad nauseum. The amount of water discarded relative to the product is awesome and the efficiency is appalling. Distillation can distinguish isotopes, but it is an extremely weak distinction, and would be even weaker for the heavier atoms used in radiodating. D2O and H2O differ in weight by a "hefty" ratio of about 20/18, where K40 and K39 would be a quarter as distinguishable by weight (40/39). It surely cannot be much compared to the basic isotope ratios that radiodating depends on, unless there were reason to expect many repetitions of the distillation. This distillation effect would have to alter ratios of stable isotopes just as easily if the weight difference is similar. If I see constant (within the intrusion) ratios of stable isotopes, I see no reason to imagine radioisotope ratios were variable. If I read an aged chart of nuclides correctly, original K40/K41 anomalies should be accompanied by much stronger K39/K41 anomalies (both appear to be stable isotopes). –Doug