¹Guillaume Leseigneur, ²Manuel Reinhardt, ¹Fatma Yesil Sahan, ³Uwe Meierhenrich
Earth and Planetary Science Letters 690, 120141 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120141]
¹Max-Planck-Institute for Solar System Research; Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²University of Göttingen, Geoscience Center, Department of Geobiology; Goldschmidtstraße 3, 37077 Göttingen, Germany
³Institut de Chimie de Nice (ICN), UMR 7272 CNRS, Université Côte d’Azur; 28 Avenue Valrose, 06108 Nice, France
Copright Elsevier

The isoprenoid alkanes pristane and phytane are widely detected in meteorites. As isoprenoids are considered markers of Earth’s biosphere, their presence in meteorites has led to a prevailing consensus that they represent terrestrial contamination, thereby calling into question the indigeneity of the entire meteoritic hydrocarbon inventory. Indeed, these chiral molecules are ubiquitous in biological systems, where their stereogenic centers are fixed and of the same absolute configuration. In this study we separate, for the first time, the different relevant chiral configurations of pristane and phytane in a meteorite sample, and we show that the isoprenoid alkanes detected in the Murchison meteorite are racemic. On Earth, racemization of these molecules has only been observed in oil shales and crude oils subjected to a certain degree of thermal maturation. In light of previous findings, these results strongly suggest that the Murchison meteorite was contaminated exclusively by petroleum pollutants present in Earth’s atmosphere, and categorically exclude any contribution from the biosphere at the fall site. Consequently, this work establishes a foundation for systematic investigations into the chirality of isoprenoids in other meteorite samples and the different sources of atmospheric petroleum pollution.

¹Line Colin, ¹Stéphane Labrosse, ¹Chloé Michaut, ²Adrien Morison
Earth and Planetary Science Letters 690, 120164 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120164]
¹Laboratoire de Géologie de Lyon: Terre, Planète, Environnement, Ecole Normale Supérieure de Lyon, Université de Lyon, Université Claude Bernard Lyon 1, Lyon,France
²Research Software Engineering, MVLS SRF, University of Glasgow, Glasgow,United Kingdom
Copyright Elsevier

The Moon presents a striking asymmetry between the nearside, which concentrates the lunar mare and shows a thin crust, and the farside, composed of thick anorthosite terranes. One proposed explanation for this asymmetry is a mantle overturn, driven by the instability of a dense, ilmenite-rich layer at the top of cumulates near the end of lunar magma ocean solidification. However, thermal instabilities may arise before the crystallization of this dense layer. In particular, material exchange by melting and crystallization at the magma ocean-cumulates boundary facilitates flow through the boundary and hence the onset of convection in the cumulates. Accounting for this flow-through interface, we investigate the onset and duration of a thermal overturn using linear stability analysis and direct numerical simulations. Our results show that a thermal overturn can initiate well before the end of magma ocean solidification, lasting from ten thousand years to tens of millions of years. The dominant convective mode corresponds to a spherical harmonic of degree one and could affect crustal growth and stabilization if the top interface is sufficiently flow-through and the Rayleigh number not too large. Taking into account the thermal evolution of the core, this early overturn could generate an early lunar dynamo.