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| Late Veneer | |
|---|---|
| Name | Late Veneer |
| Field | Planetary science |
Late Veneer is a hypothesized late-stage addition of extraterrestrial material to the Earth and other terrestrial bodies after core formation, invoked to explain elevated abundances of highly siderophile elements. The concept links geochemical observations from mantle samples, isotopic systematics, and dynamical models of the Solar System to argue for a final phase of accretion by bodies such as the Earth, Moon, Mars, and differentiated asteroids.
The late-stage accretion hypothesis synthesizes data from studies of the Earth, Moon, Mars, Mercury, and meteorite parent bodies like the HED meteorites and iron meteorites to explain anomalies in the abundances of elements such as ruthenium, iridium, platinum, palladium, and gold in silicate reservoirs. Originating in comparisons between mantle concentrations and metal-silicate partitioning measured in laboratories associated with institutions like the Geological Society of America and research groups at universities such as Caltech, Massachusetts Institute of Technology, and University of California, Berkeley, the idea interfaces with models from the Nice model, Grand Tack hypothesis, and dynamical simulations by teams at the Institut de Physique du Globe de Paris and Southwest Research Institute. It provides context for interdisciplinary discussions involving scientists affiliated with the Jet Propulsion Laboratory, NASA, European Space Agency, and laboratories at the US Geological Survey.
Geochemical support derives from mantle xenoliths, mid-ocean ridge basalt analyses, and studies of ancient cratonic materials by researchers at institutions such as Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, and the Smithsonian Institution. Isotopic systems including ruthenium isotopes, osmium isotopes, rhenium-osmium dating, tungsten isotopes (notably ^182W/^184W), and sulfur isotopes show patterns inconsistent with simple core-mantle equilibration recorded by experiments at laboratories like Oak Ridge National Laboratory and Lawrence Livermore National Laboratory. High-precision mass spectrometry developed at ETH Zurich, Columbia University, and Max Planck Institute for Chemistry revealed elevated highly siderophile element budgets in the upper mantle that better match the composition of certain chondritic meteorite classes such as CI chondrites, CM chondrites, and enstatite chondrites analyzed at facilities including the Natural History Museum, London and Field Museum of Natural History. Comparative studies of lunar samples returned by the Apollo program and analyzed by teams at the Lunar and Planetary Institute show different highly siderophile element signatures, informing calibrations used by researchers at Brown University and University of Chicago.
Potential sources include carbonaceous and ordinary chondrite reservoirs linked to regions like the asteroid belt, the Jupiter Trojan population, and outer Solar System reservoirs influenced by migrations described in the Nice model and Grand Tack hypothesis. Delivery mechanisms span residual planetesimal bombardment, giant impacts including scenarios resembling the Giant Impact Hypothesis for the origin of the Moon, and late-stage scattering of bodies during dynamical instabilities modeled by groups at Princeton University and University of Cambridge. Observational constraints come from analyses of impact-related materials in terrestrial stratigraphic records studied by researchers at the Geological Survey of Canada and isotope work by scientists at Massachusetts Institute of Technology. Meteoritic evidence from collections at the Smithsonian Institution and the Natural History Museum, London provides compositional end-members such as ordinary chondrites, carbonaceous chondrites, and differentiated achondrites.
Chronological constraints rely on isotopic chronometers including ^182Hf-^182W, ^147Sm-^143Nd, and radiometric systems developed at Carnegie Institution for Science and California Institute of Technology. Models place the late addition after metal-silicate separation associated with core formation, often within tens to hundreds of millions of years after Calcium–aluminium-rich inclusion formation and the epochs marked by events like the Late Heavy Bombardment as debated in the literature from groups at University of Arizona and Arizona State University. Numerical accretion models from teams at University of California, Santa Cruz and Imperial College London explore stochastic delivery and size-frequency distributions of impactors, while isotopic heterogeneity studies by researchers at University of Tokyo and Tohoku University refine timing relative to differentiation of bodies such as Vesta and proto-Earth growth curves in simulations using codes developed at NASA Ames Research Center.
The late veneer is invoked to reconcile Earth’s volatile inventory—elements like sulfur, phosphorus, carbon, water proxies recorded via hydrogen and oxygen isotopes—and the abundance of highly siderophile elements in the mantle with constraints from core formation experiments at University of Oxford and University of Leeds. Linkages to volatile-rich sources such as carbonaceous chondrites and cometary reservoirs assessed by teams at Jet Propulsion Laboratory and European Space Agency missions like Rosetta and Genesis are debated relative to terrestrial isotope ratios measured at University of Washington and University of Bern. The hypothesis has implications for budgets of radiogenic heat-producing elements traced by researchers at Lawrence Berkeley National Laboratory and the University of Minnesota.
Understanding a late accretion phase informs theories of planetary differentiation, core formation, and mantle convection studied by scientists at California Institute of Technology and University of Oxford, and influences scenarios for surface ocean formation and prebiotic chemistry investigated at Harvard University and University College London. Comparative planetology connecting Earth, Mars, the Moon, and asteroid parent bodies such as the HED meteorites provides context for habitability assessments used by teams at SETI Institute and spacecraft missions by NASA and European Space Agency. Constraints on timing and composition of late accretion affect models for retention of atmospheres studied by researchers at University of Colorado Boulder and influence interpretations of exoplanet formation explored by groups at Max Planck Institute for Astronomy and University of Cambridge.