A heterogeneous mantle and crustal structure formed during the early differentiation of Mars.

Highly siderophile element abundances and Os isotopes of nakhlite and chassignite meteorites demonstrate that they represent a comagmatic suite from Mars. Nakhlites experienced variable assimilation of >2-billion-year-old altered high Re/Os basaltic crust. This basaltic crust is distinct from the ancient crust represented by meteorites Allan Hills 84001 or impact-contaminated Northwest Africa 7034/7533. Nakhlites and chassignites that did not experience crustal assimilation reveal that they were extracted from a depleted lithospheric mantle distinct from the deep plume source of depleted shergottites. The comagmatic origin for nakhlites and chassignites demonstrates a layered martian interior comprising ancient enriched basaltic crust derived from trace element-rich shallow magma ocean cumulates, a variably metasomatized mantle lithosphere, and a trace element-depleted deep mantle sampled by plume magmatism.

Copper isotope composition of hemocyanin.

BACKGROUND: Copper is a metal that plays a central role in biology, for example, as co-factor in various redox enzymes. Its stable isotopic composition is being used as tracer of its transport in living organisms and as a biomarker for diseases affecting its homeostasis. While the application of copper stable isotopes to biological studies is a growing field, there are presently no biological standards that are systematically analyzed in the different laboratories, as it is the case for geological samples (e.g., by using widely available basalt samples). It is therefore paramount for the community to establish such standard. Copper also binds oxygen in the respiratory protein, hemocyanin, in the hemolymph of mollusks and arthropods and is thus critical to respiration for these species. METHODS: Here, the Cu isotope composition of hemocyanin of different modern species of mollusks and arthropods (Megathura crenulate Keyhole limpet, Limulus polyphemus Horseshoe crab and Concholepas concholepas Chilean abalone), as well as theoretical constraints on the origin of these isotopic fractionations through ab initio calculations are reported. RESULTS: The isotopic fractionation factors for Cu(I) and Cu(II), both in hemocyanin and in seawater, predict an enrichment in the lighter isotope of Cu in the hemocyanin by over 1 permil compared to seawater. The hemocyanin of Chilean abalone and Horseshoe crab have Cu isotope compositions (δ65Cu = +0.63 ± 0.04‰ and +0.61 ± 0.04‰, respectively, with δ65Cu the permil deviation of the 65Cu/63Cu ratio from the NIST SRM 976 standard), similar to that of the octopus reported in literature (+0.62‰), that are undistinguishable from seawater, suggesting quantitative Cu absorption for these organisms. Conversely, the Keyhole limpet is enriched in the lighter isotope of Cu, which is in line with the ab initio calculation and therefore Cu isotopic fractionation during incorporation of Cu into the hemocyanin. CONCLUSIONS: Because these hemocyanin standard samples are widely available, they could serve in the future as inter-laboratory standards to verify the accuracy of the Cu isotopic measurements on biological matrices.

Baseline distribution of stable copper isotope compositions of the brain and other organs in mice.

Copper (Cu) stable isotopes are useful for understanding pathways and tracing changes in Cu homeostasis, such as those induced by various diseases (e.g. liver cirrhosis, numerous forms of cancer, and neurodegenerative diseases). However, this utility relies on a baseline understanding of the natural distribution of Cu isotopes between organs of healthy organisms, which is not well-known at present. Here, the distribution of natural Cu isotopes in the brain, liver, red blood cells, plasma, kidneys, and muscle of 14 mice (7 males and 7 females) from three different genetic backgrounds is assessed. We show that the Cu isotopic composition of most mouse organs is isotopically distinct from one another. The most striking feature is the heavy isotope enrichment of the kidney (δ65Cu = 1.65 ± 0.06‰, 2SE), brain (δ65Cu = 0.87 ± 0.03‰, 2SE) and liver (δ65Cu = 0.71 ± 0.24‰, 2SE) compared to blood components, i.e. red blood cells (RBCs) (δ65Cu = 0.30 ± 0.06‰, 2SE), and plasma (δ65Cu = -0.61 ± 0.08‰, 2SE), with δ65Cu being the per mil deviation of the 65Cu/63Cu ratio from the NIST SRM 976 standard. Differences in genetic background do not appear to affect the isotopic distribution of Cu. Interestingly, male and female mice appear to have different Cu concentrations and isotopic compositions in their brain, plasma, muscle, and RBC. By demonstrating that organs have distinct isotopic compositions, our study reinforces the notion that Cu stable isotopes can be used to trace changes in homeostasis in diseases affecting Cu distribution, such as Alzheimer's disease, liver cancer, and possible chronic kidney failure.

Iron Isotopic Composition of Biological Standards Relevant to Medical and Biological Applications.

Iron isotopes are fractionated by multiple biological processes, which offers a novel opportunity to study iron homeostasis. The determination of Fe isotope composition in biological samples necessitates certified biological reference materials with known Fe isotopic signature in order to properly assess external reproducibility and data quality between laboratories. We report the most comprehensive study on the Fe isotopic composition for widely available international biological reference materials. They consist of different terrestrial and marine animal organs (bovine, porcine, tuna, and mussel) as well as apple leaves and human hair (ERC-CE464, NIST1515, ERM-DB001, ERM-BB186, ERM-BB184, ERM-CE196, BCR668, ERM-BB185, ERM-BB124). Previously measured Fe isotopic compositions were available for only two of these reference materials (ERC-CE464 tuna fish and ERM-BB186 pig kidney) and these literature data are in excellent agreement with our data. The Fe isotopic ratios are reported as the permil deviation of the 56Fe/54Fe ratio from the IRMM-014 standard. All reference materials present δ56Fe ranging from -2.27 to -0.35%0. Combined with existing data, our results suggest that animal models could provide useful analogues of the human body regarding the metabolic pathways affecting Fe isotopes, with many potential applications to medicine.

Olivine-rich achondrites from Vesta and the missing mantle problem.

Mantles of rocky planets are dominantly composed of olivine and its high-pressure polymorphs, according to seismic data of Earth's interior, the mineralogy of natural samples, and modelling results. The missing mantle problem represents the paucity of olivine-rich material among meteorite samples and remote observation of asteroids, given how common differentiated planetesimals were in the early Solar System. Here we report the discovery of new olivine-rich meteorites that have asteroidal origins and are related to V-type asteroids or vestoids. Northwest Africa 12217, 12319, and 12562 are dunites and lherzolite cumulates that have siderophile element abundances consistent with origins on highly differentiated asteroidal bodies that experienced core formation, and with trace element and oxygen and chromium isotopic compositions associated with the howardite-eucrite-diogenite meteorites. These meteorites represent a step towards the end of the shortage of olivine-rich material, allowing for full examination of differentiation processes acting on planetesimals in the earliest epoch of the Solar System.