
"The figure above shows the decay of a group of atoms of a radioactive isotope over a period of time equal to four half-lives. After two half-lives, a quarter of the original atoms remain. Three quarters have decayed to form the daughter product. After four half-lives, only one sixteenth of the original atoms will be left and fifteen sixteenths will have decayed. If we know the half-life of an isotope and we can measure both the amount of an isotope remaining and the amount of daughter product, then we can figure out how old the mineral is.
...Using the results of isotopic dating, it has become possible to put numbers on the geologic time scale, and to extend the time scale back before the occurance of abundant fossils. "
//www.stmarys.ca/conted/webcour.../isotopic.html
So, there is a process of decay we can measure. It is known. It produces a daughter element. As long as the present state of decay existed, it can be assumed it worked the same.
How long did it exist? That is the question. I say about 4400 years. Before that, the spiritual and physical state (rather than the physical only present state) saw no decay universally. The process would have likely been one that resulted in an eternal state of matter. So, the daughter material as we now call it, was then otherwise engaged, and involved in that former process.
If we look at the daughter now, the only portion of that material that was produced by decay was the bits since the split, which left us in this physical only state. Therefore, the daughter in no way can be used under any circumstances to measure age beyond the split! (The "split" refers to a time when the former spiritual and physical universe was seperated, leaving us in this temporary physical universe)
Yes it decays now, yes at a known rate. Yes there is daughter material as we call it. No it is certainly not old! Unless, of course, someone can solidly support the past as being in this same temporary decaying physical only state. It has become quite clear this can never be done. Yet, assuming a same past is the heart and soul, and very basis of all so called dating! think about it.
And isochron dating is just a similar story.