Dating is not necessary to demonstrate that evolution is a fact.Chronological sequence is all that is really required.The slope of the line determines the date, and the closeness of fit is a measure of the statistical reliability of the resulting date.Technical details on how these dates are calculated are given in Radiometric dating. As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.
When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, C is not stable.
Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air.
On Earth, natural rubidium comprises two isotopes: 72% is the stable isotope, Rb, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.
However, human beings love to see factual precision, and we want to know how old something is.
Please remember that all dating methods, even those termed "absolute," are subject to margins of error. That is a very small amount of possible error range. Modern studies almost always use two or more methods to confirm dating work and to build confidence in the results obtained.