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.rely heavily on the uranium/thorium/lead radiometric dating methods.Because it is not generally appreciated that the assumptions on which the radiometric estimates are based are a virtually impossible sequence of events, let us refresh our minds on the fundamentals of the method by turning to the hourglass analogy (Fig. This system of measuring time works well providing that: Since radioactive decay constants are believed to be unalterable, the requirement of an absolutely reproducible rate is hopefully met.Some evidence is also presented to show that radiometric results that are in agreement with the accepted geological time scale are selectively published in preference to those results that are not in agreement.The geological time scale and an age for the Earth of 4.5 b.y.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.

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.

Since 1955 the estimate for the age of the Earth has been based on the assumption that certain meteorite lead isotope ratios are equivalent to the primordial lead isotope ratios on Earth.

In 1972 this assumption was shown to be highly questionable.

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.

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.Since 1955 the estimate for the age of the Earth has been based on the assumption that certain meteorite lead isotope ratios are equivalent to the primordial lead isotope ratios on Earth.In 1972 this assumption was shown to be highly questionable.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.Up until 1972 these could be explained as being contaminated with radiogenic lead from uranium and thorium decay.