¹Haoyu Li,¹Ren T. C. Marquez,^1,2Gerrit Budde,³Haolan Tang,⁴Alexander N. Krot,⁵Marina A. Ivanova,⁶Johan Villeneuve,¹ François L. H. Tissot
Proceedings of the National Academy of Sciences 123, 29 Open Access Link to Article [10.1073/pnas.2529765123]

¹The Isotoparium, Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912
³National Key Laboratory of Deep Space Exploration/State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
⁴Hawaii Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, HI 96822
⁵Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991, Russia
⁶Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, UMR7358, Nancy F-54000, France

The 26Al-26Mg systematics in calcium–aluminum-rich inclusions (CAIs)—the oldest known Solar System solids—has traditionally been used to provide high-resolution temporal constraints on the early Solar System evolution. More recently, the study of variations in the initial Mg isotope composition has emerged as a means to probe for potential compositional heterogeneity in the nascent solar nebula. Here, we report high-precision magnesium isotope data for a collection of 19 CAIs that captures the diversity of refractory inclusions. The data reveal widespread Mg isotope heterogeneity prior to 26Al decay, covering a large range from −0.285 to +0.088‰. Combined with literature data, the distribution of Mg isotope heterogeneity in CAIs forms a continuum and no longer defines distinct populations. Our findings therefore suggest a continuous CAI formation process that captured a rapid temporal change in the composition of infalling material from the parental molecular cloud of the Solar System.