^1,2Christopher A. Parendo, ¹Stein B. Jacobsen, ¹Michail I. Petaev
Earth and Planetary Science Letters 678, 119825 Link to Articles [https://doi.org/10.1016/j.epsl.2026.119825]
¹Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United Kingdom
²Department of Earth & Planetary Sciences, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208, USA
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs), the oldest dated solids in the Solar System, preserve elemental and isotopic records of the thermal evolution of the early solar nebula—but some aspects, such as the processes driving large Ca-isotope variations, remain ambiguous. Previous studies observed isotopically light Ca in some CAIs, but whether these signatures arose from evaporation or condensation remains unresolved. We report new Ca-isotope and elemental data for 19 CAIs and 2 AOAs from the Allende meteorite and apply kinetic modeling to evaluate whether evaporation or condensation can account for the observed signatures. Our data confirm that CAIs exhibiting volatility-related REE fractionation have lighter Ca-isotope compositions than those with unfractionated REEs. Modeling demonstrates that evaporation cannot produce materials with both isotopically light Ca and near-chondritic Al/Ca ratios, requiring condensation as the cause of the observed Ca-isotope variations. Notably, modeled rates indicate that condensation occurred rapidly, over ∼10-1000 days, much faster than secular cooling of the solar nebula. These results constrain CAI thermal histories and offer insight into high-temperature processes in the early Solar System.