Figure F5. ²³⁴U/²³⁸U ratios vs. ²³⁰Th/²³⁴U. The solid line indicates the change of ²³⁴U/²³⁸U with time in the case of a closed system for uranium; the dashed line indicates the change of ²³⁴U/²³⁸U in the case of a recent loss of uranium (with ²³⁴U/²³⁸U = 1.14). Because of the analytical uncertainties, it is not possible to determine whether a closed system for uranium existed for the individual samples investigated or not.