¹C.L. Kirkland, ²M. Brown, ³P. Sutton, ¹T.E. Johnson
Earth and Planetary Science Letters 691, 120201 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120201]
¹Timescales of Mineral Systems Group, School of Earth and Planetary Sciences, Curtin University, Perth, WA, 6845, Australia
²Laboratory for Crustal Petrology, Department of Geological, Environmental, and Planetary Sciences, University of Maryland, College Park, MD, 20742-4211, USA
³School of Engineering and Physical Sciences, University of Lincoln, Lincoln, LN6 7TS, UK
Copyright Elsevier

The pock-marked surface of the Moon provides a stark reminder of the impact flux endured by the early Earth. Notwithstanding, the role of exogenic (impact-driven) processes in the generation and evolution of Earth’s continental crust has attracted relatively little attention compared to endogenic processes driven by loss of heat from the planet’s interior. Here we explore various isotope time series inferred to track crust production within the context of changing local mass density for the Solar System over the duration of its orbit through the Milky Way galaxy. Using a global dataset of zircon Hf isotopes during the Archean, we find an enhanced probability of a step change in composition during entry into the galactic spiral arms, on a periodicity of ∼190 Myr. Fluctuations in zircon oxygen isotopes between normal and non-normal distributions also reveal periods of less normality corresponding to spiral arm entry, implying the production of a greater volume of buoyant lithosphere due to an enhanced flux of energetic impacts. Additionally, the age distributions of post-Archean terrestrial hypervelocity impact craters and lunar impact-melt clasts show elevated probabilities during the predicted phases of spiral-arm crossing. For a Sun–spiral-arm recurrence interval of ∼190 Myr, the local Galactic rotation model predicts a radial epicyclic period of approximately ∼150 Myr, which is also resolved in the zircon Hf change-point record for the ancient Earth. Both frequencies have been related to periodic disturbance of the Oort cloud and modifications to the impact flux in the inner Solar System. Together, these correlations suggest that some episodes of production and reworking of continental crust during the Archean were triggered by large impacts, some of which were probably comets. That there seems to be a fundamental connection between events on Earth and the galactic tide supports a role for periods of catastrophism through Earth’s history.

¹Xi Deng, ¹Jinting Kang, ²Pei-Yi Li, ²Yun Jiang, ¹Haolan Tang, ³Yang Xiao, ^1,4Fang Huang
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.07.022]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
²Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³Sichuan Chuangyuan Weipu Analytical Technology Co., Ltd, Chengdu 610300, China
⁴Deep Space Exploration Laboratory, Hefei 230026, China
Copyright Elsevier

Rubidium (Rb) is a moderately volatile element (MVE), and its isotopic system has been widely applied to constrain evaporation and condensation processes during solar nebular evolution and planetary accretion. Tektites, natural glasses formed by the rapid melting and quenching of terrestrial crustal materials during hypervelocity impacts of extraterrestrial bodies, serve as critical geological archives for quantifying impact-driven volatile loss, particularly for MVE. Here, we report high-precision Rb isotopic data for tektites from the Australasian, North American, Central European, and Ivory Coast strewn fields, obtained via both micro-drilling (in-situ) and bulk dissolution analyses. In-situ edge–center–edge profile analyses of three australasites reveal negligible Rb concentration variations (<10%) and remarkable isotopic homogeneity, with δ87Rb ranging from –0.16 ± 0.01‰ to –0.09 ± 0.03‰ (2SD). The absence of resolvable elemental or isotopic zoning across these profiles rules out diffusion-limited evaporation as the dominant control on Rb behavior during tektite formation. Bulk δ87Rb for all analyzed tektites range from –0.22 ± 0.05‰ to –0.12 ± 0.03‰, yielding a weighted mean of –0.16 ± 0.06‰ (2SD, n = 14). This uniformity indicates no resolvable Rb isotopic fractionation and is consistent with the composition of the upper continental crust (δ87Rb = –0.14 ± 0.01‰). To further evaluate the volatility behavior of MVE under Earth-surface conditions, we perform thermodynamic modeling at ambient atmospheric pressure and oxidizing conditions. The model predicts a volatility sequence of Zn ≫ Rb ≥ K, consistent with the well-documented large Zn isotopic fractionations in tektites and the absence of measurable isotopic shifts in Rb and K. Collectively, these results may imply that Rb isotope fractionation is effectively suppressed during impact-induced evaporation under the oxidized, near-surface conditions of Earth.