The Rb-Sr ratios in various rock samples from the same lava flow might differ, but all should plot as a straight line on the graph if the lava was isotopically homogeneous (each rock sample had the same initial Sr ratio) and each rock remained closed to gain or loss of rubidium and strontium since crystallization.
In the ideal case, multiple samples from the same lava flow should plot perfectly along a line with slope e Ar give lines whose slopes supposedly reflect the ages of lava flows.
Results indicate a strong correlation between stratigraphic position of the fossil teeth and numerical age determination based on Sr content.
Furthermore, this method is equally effective for both of the fossil shark genera analyzed in the study.
Do analyses of the radioactive isotopes of rocks give reliable estimates of their ages?