In other words there was originally 4 parts per million Parentium-123 and 0 parts per million Daughterium-123.
Since there is now only 1/4 of the original amount of Parentium-123, we know that two half-lives of Parentium-123 have elapsed.
In the early 1950s, scientists established theories for using the decay of radioactive potassium (Ar) as a clock for dating certain types of rocks.
Called “noble” because it rarely bonds with other elements, argon (Ar) is one of the six noble gases.
FT thermochronology is widely used for reconstruction of low-temperature thermal histories in upper crustal rocks.The others include helium (He), neon (Ne), krypton (Kr), xenon (Xe), and radon (Rn).As one of the most abundant isotopes in the earth’s crust, K is an ideal candidate to use as a “rock clock.” Out of a wide array of available test methods, K decays.However, a whole-rock domain of a certain minimum size remains as an effectively closed system during the thermal event, and can be used to date the initial crystallisation of the rock. Isotopic evolution then occurs along near-vertical parallel paths (due to the extreme amplification of the y axis).The effects of metamorphism on mineral and whole-rock systems can also be demonstrated on the isochron diagram, Fig. During the thermal event, isotope ratios are homogenised to the whole-rock value.
Furthermore, Parentium and Daughterium are so different in chemical properties that they don't otherwise occur together.