Figure 2.

Age-probability diagrams and auxiliary plots of ⁴⁰Ar/³⁹Ar analytical data. (Top to Bottom) mols ³⁹Ar, percent radiogenic ⁴⁰Ar of total argon (⁴⁰Ar*), Ca/K ratio, and a display of individual ages. The age probabilities are calculated assuming a unit gaussian error for each analysis, followed by summation across all samples of probabilities within narrow age intervals. The dashed line in the age-probability plots represents the case where all analyses are included, whereas the solid line results from elimination of analyses falling more than two SDs beyond the mean. The omitted analyses (one from each of the four samples) are identified by ○ in the auxiliary plots above the probability diagrams. The names of samples are given at the top, with laboratory identification numbers in parentheses.