For example, a method based on a parent isotope with a very long half-life, such as C method can only be used to determine the ages of certain types of young organic material and is useless on old granites.
Some methods work only on closed systems, whereas others work on open systems.
There were other estimates but the calculations were hotly disputed because they all were obviously flawed by uncertainties in both the initial assumptions and the data.
By many experiments over the past three decades, geologists have learned which types of rocks and minerals meet these requirements and which do not.The point is that not all methods are applicable to all rocks of all ages.One of the primary functions of the dating specialist (sometimes called a geochronologist) is to select the applicable method for the particular problem to be solved, and to design the experiment in such a way that there will be checks on the reliability of the results.Sometimes these decay schemes are used individually to determine an age (e.g., Rb-Sr) and sometimes in combinations (e.g., U-Th-Pb).Each of the various decay schemes and dating methods has unique characteristics that make it applicable to particular geologic situations.he question of the ages of the Earth and its rock formations and features has fascinated philosophers, theologians, and scientists for centuries, primarily because the answers put our lives in temporal perspective.Until the 18th century, this question was principally in the hands of theologians, who based their calculations on biblical chronology.It is based on the radioactivity of Ar, however, is an inert gas that escapes easily from rocks when they are heated but is trapped within the crystal structures of many minerals after a rock cools. This correction can be made very accurately and has no appreciable effect on the calculated age unless the atmospheric argon is a very large proportion of the total argon in the analysis.The geochronologist takes this factor into account when assigning experimental errors to the calculated ages. First, there must be no argon other than that of atmospheric composition trapped in the rock or mineral when it forms.These are also the methods most commonly criticized by creation “scientists.” For additional information on these methods or on methods not covered here, the reader is referred to the books by Faul (47), Dalrymple and Lanphere (35), Doe (38), York and Farquhar (136), Faure and Powell (50), Faure (49), and Jager and Hunziker (70), as well as the article by Dalrymple (32).The K-Ar method is probably the most widely used radiometric dating technique available to geologists.