Radiometric dating assumptions
Lead204 is present in small quantities in most samples of lead, and this isotope is not itself the product of a radioactive decay process.Hence, by measuring the amount of lead-204 in a rock, geologists can estimate the amount of lead originally present.However, I hope that it will help to quell anxieties when I point out that a large number of independent methods have been applied to a vast array of different rocks.The result of this enormous array of tests is a consensus. The process rate must always have been the same" (Morris 1974a, 138).Minerals can be tested for their capacity to absorb extra argon under experimental conditions designed to resemble their natural environment, and geologists can screen out, in this way, minerals that are liable to give erroneous results.
They continue by using special techniques of their own to assign to the earth an age of a few thousand years.
Here it is possible to use two decay processes, the decay of uranium-238 into lead-206 and the decay of uranium-235 into lead-207.
Furthermore, the amount of lead originally present can be computed by considering another isotope of lead.
A second, independent, astronomical method is to use standard techniques to measure some parameters of stars (mass, luminosity, compositor, and surface temperature), from which a well-confirmed theory of the life histories of stars enables physicists to compute their. Finally, considerations of radioactive decay make it possible to calculate the time at which certain heavy elements were formed.
These techniques are somewhat similar to the radiometric methods of dating rocks, which I shad consider in a little more detail.