If the minerals in a rock have remained geochemically undisturbed since their formation, it is possible for the ages obtained by different radiometric methods (for example, the decay of ⁴⁰K to ⁴⁰Ar, ⁸⁷Rb to ⁸⁷Sr, ²³⁸U to ²⁰⁶Pb, ²³⁵U to ²⁰⁷Pb, and ²³²Th to ²⁰⁸Pb) to agree within the levels imposed by the accuracy of their known half-lives (see decay constant). If all the methods employed give a reasonable level of agreement, then the age is concordant. See radiometric dating.