¹Jesse T. Gu, ¹Rebecca A. Fischer, ¹Lucy Jacobsen, ¹Michail I. Petaev
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.01.013]
¹Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
Copyright Elsevier

Moderately volatile elements are depleted in the Earth relative to chondrites, but it remains uncertain to what extent these depletions of siderophile volatile elements are controlled by volatility versus core formation. Here, we report new metal–silicate partitioning experiments on Pb at pressures and temperatures up to 65 GPa and 5520 K, respectively. Combined with other moderately volatile elements, we use core formation models to show that homogeneous volatile accretion results in an overabundance of volatile siderophile elements relative to lithophile elements in the bulk Earth. Late volatile addition with metal–silicate equilibration at higher pressures and temperatures could potentially resolve this discrepancy by lowering bulk Earth abundances of volatile siderophile elements to be within uncertainty of the lithophile volatility trend. However, uncertainties in core formation parameters, element volatilities, volatile loss mechanisms, and the lithophile volatility trend complicate this interpretation. Our data support a relatively larger role for volatile depletion than for core formation in establishing the Pb content of the bulk silicate Earth.

^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.