Carbon dating based assumptions
This serves as strong evidence for the reliability of radiometric dating methods. These isotopes differ in the number of neutrons they have in their nuclei.
Those isotopes that are not stable decay into daughter nuclei.
Those that did the decaying are called parent nuclei.
If you have a rock that contains radioactive isotopes, these will decay over time.
This tells scientists that the sample has been disturbed and cannot be dated with this particular method.
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.
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.
The initial conditions are just read off the graph; it is not just assumed.