I don't object to having some hard evidence that there are real agreements between different methods on the geologic column, if someone can provide it. Each ring has its own characteristic radius in a given mineral in this case biotite. This radius measures the kinetic energy, hence the probability of emission of the corresponding a-particle and also the half-life of the parent nuclide according to the Geiger-Nuttall law. I even read something about geologists trying to choose crystals without impurities by visual examination when doing radiometric dating. Rubidium decays to strontium. This would also make deeper rocks tend to have older radiometric ages.
Thus such mixings cannot be detected by a mixing test.
It's the responsibility of the geologist to show that such mixings have not occurred. I don't know how we can be sure that a crystal will exclude argon or other daughter substances except by growing it in the laboratory under many conditions. We can also say that certain formations tend to give reliable dates and others do not, depending on whether the dates agree with K-Ar dates. For isochrons, which we will discuss later, the conditions are different. Age estimates on a given geological stratum by different radiometric methods are often quite different sometimes by hundreds of millions of years. How do their ages agree with the assumed ages of their geologic periods? A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years.