Creationist view of radiometric dating
If the samples have been undisturbed closed systems since formation, the data will fall on the same line (the isochron from which the diagram is named).
The slope of this line is a function of the age of the rock. The reason scientists normalize with another stable isotope of the same element as the daughter is because most chemical or physical processes that occurs normally in nature does not differentiate between different isotopes of the same element when the difference in mass is as small as it is between isotopes of the same element that is used in radiometric dating.
That is, you can see if the sample comes from rocks that have been disturbed (or contaminated) or not just by looking at the results.
Now, creationists will claim that scientists are just somehow assuming that if samples show an age that does not fit their preconceptions, the sample must be contaminated or leaky. To see why, we need to look deeper into radiometric dating methods.
Both of these are divided or normalized by a stable isotope of the same elements as the daughter element.
So on the x-axis, we have parent/(another stable isotope of the same element as the daughter) and on the y-axis we have daughter/(another stable isotope of the same element as the daughter).
Those isotopes that are not stable decay into daughter nuclei.
There are many different kinds of radiometric dating and not all conclusions we will reach can be extrapolated to all methods used.
Also, different radiometric dating techniques independently converges with each other and with other dating techniques such as dendrochronology, layers in sediment, growth rings on corals, rhythmic layering of ice in glaciers, magnetostratigraphy, fission tracks and many other methods. There exists different versions, or isotopes of many elements.
A very common claim of young earth creationists in trying to reject the evidence for an old earth is to loudly proclaim that radiometric dating methods “makes assumptions” and that these “assumptions” are somehow fatally flawed or not supported by evidence.
These claims generally land in three different categories: (1) radiometric dating assumes that initial conditions (concentrations of mother and daughter nuclei) are known, (2) radiometric dating assumes that rocks are closed systems and (3) radiometric dating assumes that decay rates are constant.
A very important tool in radiometric dating is the so called isochron diagram and it holds the key to refuting the central creationist claims about radiometric dating.