Nucleochronologies and the Mean Age of the Elements

The equations for a nucleosynthetic chronology are shown to be separable with the equations for extremely long-lived and stable nuclei yielding the mean age of the elements. This result is independent of the time-dependent production model used. This mean age is a lower bound on the age of the elements. The age of the elements is critically model-dependent. The short-lived isotopes are shown to yield the formation interval for the solar system which also is essentially model-independent. The short-lived and intermediate-lived isotopes taken relative to stable isotopes are shown to yield information on the rate of r-process nucleosynthesis with time and thus may provide the distribution of supernovae in time within the Galaxy.