In search of late-stage planetary building blocks

Genetic contributions to the final stages of planetary growth, including materials associated with the giant Moon forming impact, late accretion, and late heavy bombardment are examined using siderophile elements. Isotopic similarities between the Earth and Moon for both lithophile and siderophile elements collectively lead to the suggestion that the genetics of the building blocks for Earth, and the impactor involved in the Moon-forming event were broadly similar, and shared some strong genetic affinities with enstatite chondrites. The bulk genetic fingerprint of materials subsequently added to Earth by late accretion, defined as the addition of ~0.5 wt.% of Earth's mass to the mantle, following cessation of core formation, was characterized by 187Os/188Os and Pd/Ir ratios that were also similar to those in some enstatite chondrites. However, the integrated fingerprint of late accreted matter differs from enstatite chondrites in terms of the relative abundances of certain other HSE, most notably Ru/Ir. The final ≤0.05 wt.% addition of material to the Earth and Moon, believed by some to be part of a late heavy bombardment, included a component with much more fractionated relative HSE abundances than evidenced in the average late accretionary component. Heterogeneous 182W/184Wisotopic compositions of some ancient terrestrial rocks suggest that some very early formed mantle domains remained chemically distinct for long periods of time following primary planetary accretion. This evidence for sluggish mixing of the early mantle suggests that if late accretionary contributions to the mantle were genetically diverse, it may be possible to isotopically identify the disparate primordial components in the terrestrial rock record using the siderophile element tracers Ru and Mo.NASA grants NNX13AF83G and NNA14AB07A NSF-CSEDI grants EAR1160728 and EAR1265169

Replication Data for: Late accretionary history of Earth and Moon preserved in lunar impactites.

Abstract: Late accretion describes the final addition of Earth’s mass following Moon formation and includes a period of Late Heavy Bombardment (LHB), which occurred either as a short-lived cataclysm triggered by a late giant planet orbital instability or a declining bombardment during late accretion. Using genetically characteristic ruthenium and molybdenum isotope compositions of lunar impact–derived rocks, we show that the impactors during the LHB and the entire period of late accretion were the same type of bodies and that they originated in the terrestrial planet region. Because a cataclysmic LHB would have, in part, resulted in compositionally distinct projectiles, we conclude that the LHB reflects the tail end of accretion. This implies that the giant planet orbital instability occurred during the main phase of planet formation. Last, because of their inner solar system origin, late-accreted bodies cannot be the primary source of Earth’s water

Replication Data for: Late accretionary history of Earth and Moon preserved in lunar impactites.

Abstract: Late accretion describes the final addition of Earth’s mass following Moon formation and includes a period of Late Heavy Bombardment (LHB), which occurred either as a short-lived cataclysm triggered by a late giant planet orbital instability or a declining bombardment during late accretion. Using genetically characteristic ruthenium and molybdenum isotope compositions of lunar impact–derived rocks, we show that the impactors during the LHB and the entire period of late accretion were the same type of bodies and that they originated in the terrestrial planet region. Because a cataclysmic LHB would have, in part, resulted in compositionally distinct projectiles, we conclude that the LHB reflects the tail end of accretion. This implies that the giant planet orbital instability occurred during the main phase of planet formation. Last, because of their inner solar system origin, late-accreted bodies cannot be the primary source of Earth’s water

Replication Data for: Late accretionary history of Earth and Moon preserved in lunar impactites.

Abstract: Late accretion describes the final addition of Earth’s mass following Moon formation and includes a period of Late Heavy Bombardment (LHB), which occurred either as a short-lived cataclysm triggered by a late giant planet orbital instability or a declining bombardment during late accretion. Using genetically characteristic ruthenium and molybdenum isotope compositions of lunar impact–derived rocks, we show that the impactors during the LHB and the entire period of late accretion were the same type of bodies and that they originated in the terrestrial planet region. Because a cataclysmic LHB would have, in part, resulted in compositionally distinct projectiles, we conclude that the LHB reflects the tail end of accretion. This implies that the giant planet orbital instability occurred during the main phase of planet formation. Last, because of their inner solar system origin, late-accreted bodies cannot be the primary source of Earth’s water

Origin of 182W Anomalies in Ocean Island Basalts

Ocean island basalts (OIB) show variable 182W deficits that have been attributed to either early differentiation of the mantle or core‐mantle interaction. However, 182W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated 182W and 183W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high‐precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported 182W deficits for these samples, but also demonstrate that none of these samples have resolvable 183W anomalies. These data therefore rule out a nucleosynthetic origin of the 182W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late‐accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the 182W composition of the bulk mantle to its modern‐day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of 182W deficits in OIB from the addition of either core or late‐accreted material, but only if these materials have a non‐carbonaceous (NC) meteorite‐like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)‐like materials to either Earth's core or late accretion.Plain Language Summary: Some ocean island basalts (OIB) may contain a record of processes and characteristics of the deepest parts of Earth's mantle, including at the boundary between the iron‐rich core and mantle. Like some prior studies, we measured tungsten isotopes within OIB from Hawaii and Samoa, and report that tungsten isotopes in these OIB differ in their characteristics compared to what is observed in modern rocks that are most representative of the upper part of Earth's mantle. One explanation for these tungsten isotope anomalies is that they are a signature of chemical interaction between the core and lower mantle, suggesting that the core 'leaks' into the lower mantle. Another possibility proposed here is that these tungsten isotope anomalies reflect ancient crust that contained dense, meteorite‐like materials, which sank to the bottom of the mantle during Earth's early history. Using isotopes of another element, molybdenum, we show that the source(s) of these tungsten isotope anomalies do not contain a significant number of materials that originated from the outer Solar System before being added to Earth during its formation.Key Points: 182W deficits in ocean island basalts are confirmed, but correlated 182W–183W anomalies present in prior datasets are not confirmed. 182W deficits may reflect core‐mantle interaction or an overabundance of late‐accreted materials, but not nucleosynthetic effects. Mo isotope data similar to BSE estimate; W‐Mo data rule out significant contribution of CC‐like material to Earth's core or late accretion.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659https://doi.org/10.35003/YCUKO

Gamete Recognition Gene Divergence Yields a Robust Eutherian Phylogeny across Taxonomic Levels

The extraordinary morphological diversity among extant mammals poses a challenge for studies of speciation, adaptation, molecular evolution, and reproductive isolation. Despite the recent wealth of molecular studies on mammalian phylogenetics, uncertainties remain surrounding both ancestral and more recent divergence events that have proven difficult to resolve. Multi-gene datasets, especially including genes that are highly divergent, often provide increased support for higher-level affinities within Mammalia; however, such analyses require vast amounts of genomic sequence data and at times, intensive, high-performance computational effort. Furthermore, despite the large-scale efforts dedicated to comprehensive, multi-gene phylogenetic analyses using a combination of mitochondrial, nuclear, and other sequences (e.g., tRNA, ultra-conserved elements, and transposable elements), many relationships across Mammalia remain highly controversial. To offer another approach and provide a phylogenetic solution to this longstanding issue, here we present a phylogenetic tool based on a single reproductive molecular marker, zonadhesin (gene: Zan), one of two known mammalian speciation genes, which encodes the rapidly evolving sperm protein zonadhesin that mediates species-specific adhesion to the egg and thereby promotes reproductive isolation among placental mammals (Eutheria). Topological comparison of Zan Maximum Likelihood phylogenies to a nearly complete mammalian supertree confirmed Zan’s striking phylogenetic utility and resolution at both deeper and more terminal nodes in the placental mammalian phylogeny. This single gene marker yielded an equivalent and/or superiorly supported topology in comparison to a supertree generated using DNA sequences from a supermatrix of 31 genes from 5911 species (extinct and extant). Resolution achieved with this new phylogenetic approach provides unique insights into the divergence of both early and recent mammalian radiations. Finally, and perhaps most importantly, the utility of zonadhesin as a singular molecular marker was especially useful in clades where sufficient taxon sampling is impossible to achieve, and where only a subset of members of the mammalian species tree is available. The eutherian relationships presented here provide a foundation for future studies in the reconstruction of mammalian classifications, including reproductive isolation, hybridization, and biodiversification of species

Distinct evolution of the carbonaceous and non-carbonaceous reservoirs: Insights from Ru, Mo, and W isotopes

Recent work has identified a nucleosynthetic isotope dichotomy between carbonaceous (CC) and non-carbonaceous (NC) meteorites. Here, we report new Ru isotope data for rare iron meteorite groups belonging to the NC and CC suites. We show that by studying the relative isotopic characteristics of Ru, Mo, and W in iron meteorites, it is possible to constrain the processes leading to the distinct isotope heterogeneities in both reservoirs. In NC meteorites, internally normalized, mass-independent isotope ratios of Mo and Ru are correlated, but those of Mo and W are not. In CC meteorites, Mo and W isotope ratios are correlated, but those of Mo and Ru are not; specifically, Mo isotopic compositions are variable and those of Ru are more restricted. The contrasting behaviors of Ru and W relative to Mo in the two reservoirs likely require processing of the presolar carriers under distinct redox conditions. This provides further evidence that NC and CC meteorites originated from spatially separated reservoirs that evolved under different prevailing conditions. (C) 2019 Elsevier B.V. All rights reserved

Origin of 182W Anomalies in Ocean Island Basalts

Abstract Ocean island basalts (OIB) show variable 182W deficits that have been attributed to either early differentiation of the mantle or core‐mantle interaction. However, 182W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated 182W and 183W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high‐precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported 182W deficits for these samples, but also demonstrate that none of these samples have resolvable 183W anomalies. These data therefore rule out a nucleosynthetic origin of the 182W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late‐accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the 182W composition of the bulk mantle to its modern‐day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of 182W deficits in OIB from the addition of either core or late‐accreted material, but only if these materials have a non‐carbonaceous (NC) meteorite‐like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)‐like materials to either Earth's core or late accretion

Replication Data for: Origin of 182W anomalies in ocean island basalts

• 182W deficits in ocean island basalts are confirmed using a new method • Correlated 182W-183W anomalies that are present in prior datasets are not confirmed, ruling out a nucleosynthetic origin for 182W deficits • 182W deficits may reflect either core-mantle interaction or an overabundance of late-accreted materials • Mo isotope data do not reveal resolved nucleosynthetic anomalies • Combined W-Mo data rule out significant contribution of CC-like material to Earth’s core or late accretio

Replication Data for: Origin of 182W anomalies in ocean island basalts

• 182W deficits in ocean island basalts are confirmed using a new method • Correlated 182W-183W anomalies that are present in prior datasets are not confirmed, ruling out a nucleosynthetic origin for 182W deficits • 182W deficits may reflect either core-mantle interaction or an overabundance of late-accreted materials • Mo isotope data do not reveal resolved nucleosynthetic anomalies • Combined W-Mo data rule out significant contribution of CC-like material to Earth’s core or late accretio