¹Sandrine Péron, ¹Sujoy Mukhopadhyay
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.01.002]
¹Department of Earth and Planetary Sciences, University of California, Davis, Davis, CA 95616, USA
Copyright Elsevier

Accretion of volatile elements is a critical step to make a planet habitable. It is often assumed that terrestrial planets initially captured solar gases from the nebula, which are partially ingassed into their interior during the magma ocean phase, and then chondritic and/or cometary volatiles are delivered during the main accretion phase or after. Recent krypton isotopic measurements of the Martian meteorite Chassigny have however shown that chondritic volatiles were acquired on Mars in the first Myr of Solar System formation before nebular capture. Yet, Martian mantle is heterogeneous, with multiple reservoirs as evidenced with the hydrogen isotopic composition of shergottites, and it is unclear if this is also the case for noble gases. In this study, we investigate the noble gas (Ne, Ar, Kr, Xe) isotopic and elemental composition of the chassignite NWA 8694, which constitutes a link between chassignites and nakhlites, via laser step-heating in order to assess potential heterogeneities of the Martian mantle. Similar to Chassigny, we found evidence for high Ar, Kr and Xe abundances, potentially at least one order of magnitude higher than in the Earth’s mantle, in the NWA 8694 mantle source based on a low 40Ar/36Ar ratio. We also found a chondritic component and a Martian atmospheric component in NWA 8694, the latter with fractionated Ar/Kr/Xe elemental ratios compared to Mars’ atmosphere. This Martian atmosphere component was possibly introduced through aqueous alteration by surface fluids, as observed in MIL nakhlites. The chondritic component corresponds to the composition of the NWA 8694 mantle source and hence confirms previous observation in Chassigny. A chondritic Martian mantle is in stark contrast with the presence of solar Kr and Xe in the Martian atmosphere. This suggests that chondritic volatiles were delivered to terrestrial planets in the first Myr of Solar System formation in presence of the nebula. Solar gases in the atmosphere could have been captured from the nebula afterwards or delivered by material similar to comets. If captured from the nebula, it would require the solar gases to be trapped either in polar ice caps or the regolith so as not to be lost via hydrodynamic escape after the nebula dissipates. Alternatively, delivery of solar gases associated with comets could occur after cessation of hydrodynamic escape on Mars, but the one comet (67P/C-G) that has been measured so far does not show a pure solar-like Xe and Kr isotopic composition.

¹Jiawen Zhao, ¹Koichi Mimura
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.01.003]
¹Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan
Copyright Elsevier

The abiotic supply of phospholipid precursors on the early Earth constitutes a critical stage in cellular evolution. Glycerophosphate (GP) and acylglycerol (AG) are potential precursors to the bonding of polar heads and lipidic chains attached to the glycerol backbone in phospholipids. A deeper understanding of the synthesis of GP and AG on early Earth is essential for unraveling the origin of life. In this study, we performed shock experiments to simulate the impact of extraterrestrial bodies on both wet and dry surfaces of early Earth to investigate the synthesis of GP and AG. These experiments were conducted in the temperature transition zone between negligible alteration and complete decomposition of organic materials. Despite GP and AG synthesis involving dehydration, our experiments revealed they can synthesize under both wet and dry conditions by impact shock. This suggests that the process occurs universally in both wet and dry environments and presents a feasible pathway for phosphorylation and acylation on the early Earth. Moreover, the crater created by the impact may evolve into “warm little ponds” that collect the synthesized GP and AG for further evolution. The dry-wet cycles in the ponds not only facilitate the assembly of vesicles but also provide opportunities for further evolution. Our findings indicate that impacts from extraterrestrial bodies may have contributed to cellular evolution by supplying phospholipid precursors on the early Earth.