Nucleosynthetic Zn isotope anomalies reveal the heritage of Earth’s volatiles

Determining the provenance of volatile elements in Earth is key for understanding the processes that led to its habitability. Based on volatile element abundances and H and N isotope data it has been argued that Earth’s volatile element inventory largely stems from the addition of volatile-rich outer solar system (CC) material to a volatile-poor protoEarth made of inner solar system (NC) material [1-2]. However, recent work has shown that an inner or outer solar system origin of Earth's volatiles cannot be distinguished by these approaches [3]. Nucleosynthetic isotope anomalies might offer a direct way of identifying the origin of the volatile materials accreted by Earth [4], however, until now, no such anomalies have been identified for volatile elements. Here, we report the detection of isotope anomalies for the moderately volatile element Zn. Using a comprehensive set of meteorites we show that Zn exhibits the same fundamental isotopic dichotomy between NC and CC materials as non-volatile elements. Terrestrial Zn has an isotopic composition between NC and CC bodies, demonstrating that Earth accreted Zn from both, the inner and outer Solar System. Extending this finding to other volatile elements, and combing the Zn data with anomalies in non-volatile elements yields a coherent picture of the fraction and nature of CC materials in Earth, and thus their relevance for its habitability.

[1] Braukmüller et al., 2019 Nat. Geosci. 12 [2] Marty, 2012 EPSL 313–314 [3] Piani et al., 2020 Science 369 [4] Burkhardt et al., 2021 Sci. Adv. 7