That difficulty aside, they were selected because they contain very little uranium and thorium and are therefore unlikely to contain significant radiogenic lead.
“This (work) shows unequivocally for the first time that there is indeed a real problem in the uranium/lead evolution in meteorites, in that in each of these meteorites there is now insufficient uranium to support the lead isotope composition.
“It therefore follows that the whole of the classical interpretation of the meteorite lead isotope data is in doubt, and that the radiometric estimates of the age of the Earth are placed in jeopardy.” In plain language, the radiometric estimates for the age of the earth are lacking real foundations.
The radiometric dating method is basically an extrapolation of the form shown in Fig. If the decay constant is known with great accuracy, an extrapolation over one or two thousand years may be regarded as quite reasonable. It should be obvious that the further one projects present rates, the more likely one is to be quite wrong. era started about 1955 with the publication of a classic paper by Patterson In spite of cautions and scepticism advised by the authors this number has been widely and enthusiastically accepted and is usually quoted as if the evidence was decisive and conclusive. Lead-206 and lead-207 are known daughter products from the decay of uranium-238 and uranium-235, respectively.
It has assumed something of the status of a universal constant to which all other data must be fitted, thus it has become common practice to assume that data which does not fit this result is either wrong or unintelligible. Lead-204, a minor isotope of common lead, has no radioactive parent and is believed to be primordial lead.
It might be argued that although radiometric dating has a few problems, the large body of concordant data using different isotopes shows that the dates are of the right order.