Radiometric dating of rocksfossils
Before 1955, ages for the Earth based on uranium/thorium/lead ratios were generally about a billion years younger than the currently popular 4.5 billion years. old Earth is reviewed and deficiencies of the uranium/lead method are discussed.The basic theory of radiometric dating is briefly reviewed.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.Lead-206 and lead-207 are also believed to be present in primordial lead since there is insufficient uranium to account for all the lead.Just how much lead-206 and 207 were present at the beginning, nobody knows. As a uranium ore ages, the ratio of lead-206 to lead-204 increases as does the ratio of lead-206 to lead-207.Despite this, the momentum gained in the two decades prior to 1972 has made 4.5 b.y.a popularly accepted “universal constant” even though the foundations on which it was based have been virtually removed.
Therefore, since the lead isotope ratios for the majority of meteorites are the same as present day common lead ratios and may also be assumed to represent primordial lead, the billion year age chronology disappears.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.That difficulty aside, they were selected because they contain very little uranium and thorium and are therefore unlikely to contain significant radiogenic lead.However, it is even more surprising to learn that the lead isotope ratios chosen by Patterson Most meteorites have lead isotope ratios similar to those of present day common lead.