Radiogenic dating of meteorites
The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth.
The equation is the one which describes radioactive decay: If one of these assumptions has been violated, the simple computation above yields an incorrect age.
The wonderful property of isochron methods is: if one of these requirements is violated, it is nearly certain that the data will indicate the problem by failure to plot on a line.
(This topic will be discussed in much more detail below.) Where the simple methods will produce an incorrect age, isochron methods will generally indicate the unsuitability of the object for dating.
The amount of initial wouldn't change over time -- because it would have no parent atoms to produce daughter atoms.However, the methods must be used with care -- and one should be cautious about investing much confidence in the resulting age...especially in absence of cross-checks by different methods, or if presented without sufficient information to judge the context in which it was obtained.Age "uncertainty" When a "simple" dating method is performed, the result is a single number.There is no good way to tell how close the computed result is likely to be to the actual age.