0.714 0.712 0.710 0.703 0.706 0.704 0.702 0.700 0.10 0.15 8TRbSr FIGURE 20.19 Relative abundance determinations...
0.714 0.712 0.710 0.703 0.706 0.704 0.702 0.700 0.10 0.15 8TRbSr FIGURE 20.19 Relative abundance determinations for a sample obtained in the lunar highlands. (Data from D. A. Papanastassiou and G J. Wasserburg, Proc. Seventh Lunar Sei Conf Pergamon Press, New York, 1976.) Example 20.4.1. Data for one sample obtained in the lunar highlands, based on the beta decay 14 of rubidium-87to strontium-87.3gRb → ISr + e-+5, are shown in Fig. 20.19 From Eq. (20.1) and Fig. 20.19 where λ = 0.0146 x 10-9 yr-1 for #Rh Solving for t, we find that the age of the sample is 4.39 x 10 yr It is important to point out that this procedure assumes that the initial ratio Sr/Sr is a constant throughout the sample, whereas the initial ratio Rbmay vary somewhat (ie.. the sample is not perfectly homogeneous). This is because Sr and Sr are chemically identical, allowing them to be bound up in minerals in the same proportions, whereas the proportion of RbSr need not be constant throughout. 3838 TABLE 20.2 Results from the Analysis of Basalt 10072, Returned from the Sea of Tranquility by the Apollo 11 Astronauts in 1969. (Data from D. A. Papanastassiou, D. J. DePaolo, and G J Wasserburg. "Rb-Sr and Sm-Nd Chronology and Genealogy of Mare Basalts from the Sea of Tranquility, Proceedings of the Eighth Lunar Science Conference, Pergamon Press, New York, 0.1847 0.1963 0.1980 0.511721土18 0.51 1998 ± 16 0.512035 ± 21 0.512238 ± 17 0.5 1 3788土15 0.514154 17 0.2715 0.2879