Figure F3. ²³¹Pa/²³⁵U vs. ²³⁰Th/²³⁴U ratios of samples investigated. In the case of an age concordance, the ratios fall on the solid line; this concordia curve was calculated using Equations 1 and 2 with an initial ²³⁴U/²³⁸U = 1.14. Numbers in frames refer to sample number. Horizontal lines are isochrons and associated numbers indicate ages.