U-TH-PB DATING: AN EXAMPLE OF FALSE ISOCHRONS
"Excerpted the Conclusion fro above link
The concerns raised by Zheng [28] regarding U-Pb isochrons are warranted. At Koongarra a 207Pb/206Pb “isochron” produced from 11 hand-picked uraninite and galena grains, plus four whole-rock samples, yields an “age” of 863 Ma, the same as a near-concordant “age” from one of the uraninite grains. Nine weathered whole-rock samples yield an “isochron age” of 1270Ma, while 113 soil samples produce an excellent “isochron” with an “age” of 1445Ma. All of these “ages” are geologically meaningless. While the apparent isochron produced by the soil samples may be identified as a mixing line, produced by the mixing of radiogenic Pb with common or background Pb in the surrounding rocks and soils, even this explanation strains credulity because the samples come from up to 17km away from known uranium mineralization, and a few of the soil samples represent different rock types. Not only then has open system behavior of these isotopes been demonstrated, but apparent “isochrons” and their derived “ages” are invariably geologically meaningless. Thus none of the assumptions used to interpret the U-Th-Pb isotopic system to yield “ages” can be valid. If these assumptions were valid, then the 232Th/208Pb “age” of 0Ma for three of the five uraninite samples should be taken seriously. Creationists should therefore not be intimidated by claims that U-Th-Pb radiometric “dating” has “proved” the presumed great antiquity of the earth, and the strata and fossils of the so-called geological column. "