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It is probably because of this type of evidence for extensive mixing in the alteration zone that Patterson “In view of the evidence for extensive mixing, it would seem contrary to the facts to postulate differing frozen lead/uranium ratios that have existed for billions of years.
The requirements of the assumptions in the lead ore method are so extreme it is unlikely that it should give a correct age.” So they took a different approach.
Up until 1972 these could be explained as being contaminated with radiogenic lead from uranium and thorium decay.
In 1972, however, Gale showed unequivocally that there is by no means sufficient uranium and thorium to account for what could previously have been called radiogenic lead.
These ratios for many lead ores are plotted in Fig. The lowest ratios are taken to be the most ancient ores, formed at the beginning, billions of years ago and separated from further radiogenic enrichment. They show that widespread contamination and differentiation from various sources of lead have occurred during the more than one thousandfold concentration into the present lead ore deposits. There is no discontinuity whatever between results lying in the time clock zone and those lying in the alteration zone. Since there is no reason why the alteration zone should not extend into what is classified as the time clock zone (apart from a belief in 4.5 b.y.), the majority of the data can be explained as indicating a history of geochemical alteration.
In 1955 a symposium on radiometric dating was held from which the following was given in the summary: “Radioactive ‘dating’ has been perhaps the most widely publicised of geochemical techniques, but of several known dating methods based on radioactivity, only C-14 dating has developed to the point where it yields consistently reliable ages.
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.
“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.
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In case the significance of these results is ignored, a few sentences from the Gale “ …