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Lunar magmatic rocks are shown to be enriched in the heavy isotopes of zinc and to have lower zinc concentrations than terrestrial or Martian igneous rocks; these variations represent the large-scale evaporation of zinc, most probably in the aftermath of the Moon-forming giant impact event. Zinc supports giant-impact theory of Moon formation The heavily favoured theory for the origin of the Earth–Moon system is a giant impact between the proto-Earth and a Mars-sized body. Such a cataclysmic event would have left its mark on the isotopic composition of the Moon, because light isotopes evaporate more readily than heavier ones. Zinc in particular is a powerful indicator of the volatile histories of planets — it undergoes strong isotopic fractionation in planetary rocks, but is hardly fractionated following volcanic activity on Earth. This study compares high-precision zinc isotopic data for lunar basalts, Martian meteorites and terrestrial igneous rocks, and finds that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or Martian samples. The authors conclude that these variations are the result of large-scale evaporation of zinc in the aftermath of the Moon-forming giant-impact event. Volatile elements have a fundamental role in the evolution of planets. But how budgets of volatiles were set in planets, and the nature and extent of volatile-depletion of planetary bodies during the earliest stages of Solar System formation remain poorly understood 1 , 2 . The Moon is considered to be volatile-depleted and so it has been predicted that volatile loss should have fractionated stable isotopes of moderately volatile elements 3 . One such element, zinc, exhibits strong isotopic fractionation during volatilization in planetary rocks 4 , 5 , but is hardly fractionated during terrestrial igneous processes 6 , making it a powerful tracer of the volatile histories of planets. Here we present high-precision zinc isotopic and abundance data which show that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or Martian igneous rocks. Conversely, Earth and Mars have broadly chondritic zinc isotopic compositions. We show that these variations represent large-scale evaporation of zinc, most probably in the aftermath of the Moon-forming event, rather than small-scale evaporation processes during volcanism. Our results therefore represent evidence for volatile depletion of the Moon through evaporation, and are consistent with a giant impact origin for the Earth and Moon.

Core formation should have stripped the terrestrial, lunar, and martian mantles of highly siderophile elements (HSEs). Instead, each world has disparate, yet elevated HSE abundances. Late accretion may offer a solution, provided that ≥0.5% Earth masses of broadly chondritic planetesimals reach Earth's mantle and that approximately 10 and approximately 1200 times less mass goes to Mars and the Moon, respectively. We show that leftover planetesimal populations dominated by massive projectiles can explain these additions, with our inferred size distribution matching those derived from the inner asteroid belt, ancient martian impact basins, and planetary accretion models. The largest late terrestrial impactors, at 2500 to 3000 kilometers in diameter, potentially modified Earth's obliquity by approximately 10°, whereas those for the Moon, at approximately 250 to 300 kilometers, may have delivered water to its mantle.

Sample return missions have provided the basis for understanding the thermochemical evolution of the Moon. Mare basalt sources are likely to have originated from partial melting of lunar magma ocean cumulates after solidification from an initially molten state. Some of the Apollo mare basalts show evidence for the presence in their source of a late-stage radiogenic heat-producing incompatible element-rich layer, known for its enrichment in potassium, rare-earth elements, and phosphorus (KREEP). Here we show the most depleted lunar meteorite, Asuka-881757, and associated mare basalts, represent ancient (~3.9 Ga) partial melts of KREEP-free Fe-rich mantle. Petrological modeling demonstrates that these basalts were generated at lower temperatures and shallower depths than typical Apollo mare basalts. Calculated mantle potential temperatures of these rocks suggest a relatively cooler mantle source and lower surface heat flow than those associated with later-erupted mare basalts, suggesting a fundamental shift in melting regime in the Moon from ~3.9 to ~3.3 Ga. Ancient (~3.9 Ga) KREEP-free basalts were sourced from a relatively cool and shallow pyroxene-rich mantle distinct from later-erupted (<3.8 Ga) KREEP-bearing basalts, indicating a fundamental change in melting regimes in the Moon.

New tungsten isotope data for modern ocean island basalts (OIB) from Hawaii, Samoa, and Iceland reveal variable 182W/184W, ranging from that of the ambient upper mantle to ratios as much as 18 parts per million lower. The tungsten isotopic data negatively correlate with ³He/⁴He. These data indicate that each OIB system accesses domains within Earth that formed within the first 60 million years of solar system history. Combined isotopic and chemical characteristics projected for these ancient domains indicate that they contain metal and are repositories of noble gases. We suggest that the most likely source candidates are mega–ultralow-velocity zones, which lie beneath Hawaii, Samoa, and Iceland but not beneath hot spots whose OIB yield normal 182W and homogeneously low ³He/⁴He.

Halogen abundances in chondrites are 6 to 37 times lower than previously reported, which is consistent with the low abundances of these elements found in Earth. An Earthly halogen history The heavy halogens chlorine (Cl), bromine (Br) and iodine (I) are key tracers of accretion during the formation of Earth owing to their high volatility and incompatibility. Patricia Clay and co-authors show that the abundances of these heavy halogens in carbonaceous, enstatite, Rumuruti and ordinary chondrites are much lower than reported previously. The authors also find that the Br/Cl and I/Cl ratios in all the chondrites studied show a limited range, indistinguishable from bulk silicate Earth estimates. This indicates that the depletion of halogens relative to primitive meteorites is consistent with lithophile elements of similar volatility. They conclude that the observed terrestrial halogen inventories cannot be explained by late accretion alone, but also require the efficient extraction of halogen-rich fluids from the solid Earth during the earliest stages of its formation. Volatile element delivery and retention played a fundamental part in Earth’s formation and subsequent chemical differentiation. The heavy halogens—chlorine (Cl), bromine (Br) and iodine (I)—are key tracers of accretionary processes owing to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. However, noble gas proxy isotopes produced during neutron irradiation provide a high-sensitivity tool for the determination of heavy halogen abundances. Using such isotopes, here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites are about 6 times, 9 times and 15–37 times lower, respectively, than previously reported and usually accepted estimates 1 . This is independent of the oxidation state or petrological type of the chondrites. The ratios Br/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth estimates. Our results demonstrate that the halogen depletion of bulk silicate Earth relative to primitive meteorites is consistent with the depletion of lithophile elements of similar volatility. These results for carbonaceous chondrites reveal that late accretion, constrained to a maximum of 0.5 ± 0.2 per cent of Earth’s silicate mass 2 , 3 , 4 , 5 , cannot solely account for present-day terrestrial halogen inventories 6 , 7 . It is estimated that 80–90 per cent of heavy halogens are concentrated in Earth’s surface reservoirs 7 , 8 and have not undergone the extreme early loss observed in atmosphere-forming elements 9 . Therefore, in addition to late-stage terrestrial accretion of halogens and mantle degassing, which has removed less than half of Earth’s dissolved mantle gases 10 , the efficient extraction of halogen-rich fluids 6 from the solid Earth during the earliest stages of terrestrial differentiation is also required to explain the presence of these heavy halogens at the surface. The hydropilic nature of halogens, whereby they track with water, supports this requirement, and is consistent with volatile-rich or water-rich late-stage terrestrial accretion 5 , 11 , 12 , 13 , 14 .

Highly siderophile elements (HSE), including platinum, provide powerful geochemical tools for studying planet formation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE. However, core formation could also have contributed to the mantle’s HSE content. Here we present measurements of platinum metal-silicate partitioning coefficients, obtained from laser-heated diamond anvil cell experiments, which demonstrate that platinum partitioning into metal is lower at high pressures and temperatures. Consequently, the mantle was likely enriched in platinum immediately following core-mantle differentiation. Core formation models that incorporate these results and simultaneously account for collateral geochemical constraints, lead to excess platinum in the mantle. A subsequent process such as iron exsolution or sulfide segregation is therefore required to remove excess platinum and to explain the mantle’s modern HSE signature. A vestige of this platinum-enriched mantle can potentially account for 186 Os-enriched ocean island basalt lavas. Through platinum metal-silicate partitioning coefficient measurements, the authors here show that platinum partitioning into metal is lowered at high pressure–temperature conditions. This finding implies that the Earth’s mantle was likely enriched in platinum immediately following the core-mantle differentiation.

The abundance and distribution of water within Mars through time plays a fundamental role in constraining its geological evolution and habitability. The isotopic composition of Martian hydrogen provides insights into the interplay between different water reservoirs on Mars. However, D/H (deuterium/hydrogen) ratios of Martian rocks and of the Martian atmosphere span a wide range of values. This has complicated identification of distinct water reservoirs in and on Mars within the confines of existing models that assume an isotopically homogenous mantle. Here we present D/H data collected by secondary ion mass spectrometry for two Martian meteorites. These data indicate that the Martian crust has been characterized by a constant D/H ratio over the last 3.9 billion years. The crust represents a reservoir with a D/H ratio that is intermediate between at least two isotopically distinct primordial water reservoirs within the Martian mantle, sampled by partial melts from geochemically depleted and enriched mantle sources. From mixing calculations, we find that a subset of depleted Martian basalts are consistent with isotopically light hydrogen (low D/H) in their mantle source, whereas enriched shergottites sampled a mantle source containing heavy hydrogen (high D/H). We propose that the Martian mantle is chemically heterogeneous with multiple water reservoirs, indicating poor mixing within the mantle after accretion, differentiation, and its subsequent thermochemical evolution.Mars’s mantle is chemically heterogeneous and contains multiple primordial water reservoirs, according to an analysis of the hydrogen isotopic composition of minerals in Martian meteorites.

Appendicoliths are commonly found obstructing the lumen of the appendix at the time of appendectomy. To identify factors that might contribute to their formation we investigated the composition of appendicoliths using laser ablation inductively coupled plasma mass spectroscopy, gas chromatography, polarized light microscopy, X-ray crystallography and protein mass spectroscopy. Forty-eight elements, 32 fatty acids and 109 human proteins were identified within the appendicoliths. The most common elements found in appendicoliths are calcium and phosphorus, 11.0 ± 6.0 and 8.2 ± 4.2% weight, respectively. Palmitic acid (29.7%) and stearate (21.3%) are the most common fatty acids. Some stearate is found in crystalline form—identifiable by polarized light microscopy and confirmable by X-ray crystallography. Appendicoliths have an increased ratio of omega-6 to omega-3 fatty acids (ratio 22:1). Analysis of 16 proteins common to the appendicoliths analyzed showed antioxidant activity and neutrophil functions (e.g. activation and degranulation) to be the most highly enriched pathways. Considered together, these preliminary findings suggest oxidative stress may have a role in appendicolith formation. Further research is needed to determine how dietary factors such as omega-6 fatty acids and food additives, redox-active metals and the intestinal microbiome interact with genetic factors to predispose to appendicolith formation.