concordant age 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.
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