In order to use these methods, we have to start out with a system in which no daughter element is present, or else know how much daugher element was present initially so that it can be subtracted out.
We also need to know that no parent or daughter has entered or left the system in the meantime.
For potassium 40, the half-life is about 1.3 billion years.
In general, in one half-life, half of the parent will have decayed.
We are told that of all the radiometric dates that are measured, only a few percent are anomalous.
This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points.
If these conditions are not satisfied, the error can be arbitrarily large.I believe that there is a great need for this information to be made known, so I am making this article available in the hopes that it will enlighten others who are considering these questions.Even the creationist accounts that I have read do not adequately treat these issues.In two half-lives, half of the remainder will decay, meaning 3/4 in all will have decayed.In general, in n half-lives, only 1/(2^n) of the original parent material will be left.