Fig. 2.

(Top) Mean [²³⁸U] and ²³²Th/²³⁸U ratios (Middle) from LA ICP-MS for 17 eggshells from YFT1 magnified image of the radial cross-section of one eggshell polished in an epoxy mount (Bottom), showing the structural transitions in the eggshell corresponding with changes in U and Th concentrations. Abbreviations for structural changes in the red inset image are as follows: V, vertical crystal layer; P, palisade layer; and C, cone layer. Location of the inset image is shown in the red box in the image of the polished eggshell mount (Lower Left); (Lower Right) original eggshell fragment before sample preparations, from LG 1 at YFT1. For all individual LA profiles and sample images, reference SI Appendix.