¹Coral K. Chen, ²Meng Guo, ¹Jun Korenaga, ³Simone Marchi
Earth and Planetary Science Letters 666, 119493 Link to Article [https://doi.org/10.1016/j.epsl.2025.119493]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06520, United States of America
²Asian School of the Environment, Nanyang Technological University, 600259, Singapore
³Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, United States of America
Copyright Elsevier

As an important reservoir for incompatible elements, the growth of the continental crust profoundly influenced the composition of the mantle and the atmosphere. The co-evolution of the continental crust, mantle, and atmosphere throughout Earth history can be traced through the transfer of argon and potassium between these three reservoirs. While many argon-constrained crustal growth models have been proposed, none of them consider the effect of late accretion (bombardment by leftover planetesimals in the several hundred million years after the Moon formed) in detail. Our model is the first of its kind to simulate both the volatile delivery and the atmospheric erosion by impacting planetesimals. Whereas the relative fraction of impactor-derived argon in the present-day atmosphere depends on the assumed impactor composition and the starting atmospheric mass, the present-day atmospheric argon originates largely from mantle degassing and crustal processing. For a range of impact parameters, our model results indicate that the early rapid growth of continental crust is required to satisfy the argon budget of the mantle and atmosphere.

¹William M. Lawrence, ¹Geoffrey A. Blake,¹John Eiler
Proceedings of the National Academy of Sciences of the USA (PNAS) 122, e2423345122 Link to Article [https://doi.org/10.1073/pnas.2423345122]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125

Macromolecular organic solids found in primitive meteorites were the main source of carbon delivered to forming planets in the early Solar System. However, the conditions under which this material formed and its subsequent incorporation into growing planetesimals remains a subject of vigorous debate. Here, we show that C isotope variations among these organics in most carbonaceous chondrites are strongly correlated with mass-independent O isotope anomalies exhibited by their host meteorites. As the latter signature has been argued to track abundances of nebular water generated from photochemical processing of CO gas, the C isotope variability of refractory organic solids may relate to this same process. We propose a framework in which CO photolysis simultaneously produces H2O and generates a pool of C+ ions that serve as precursors for C-rich organic solids, with their C isotope compositions suggesting formation over a relatively narrow and warm range of temperatures in the protoplanetary disk (~200 to 400 K). Two populations of organic precursors with different C isotope compositions became associated with distinct dust reservoirs prior to their delivery to the carbonaceous-chondrite-forming region, which likely resided at lower temperatures (<170 K). This finding places detailed constraints on the location and distribution of chemical reactions that generated both water and organic-rich reservoirs in the early Solar System.