Resolving the timing of crustal processes and meteorite impact events is central to understanding the formation, evolution and habitability of planetary bodies. However, identifying multi-stage events from complex planetary materials is highly challenging at the length scales of current isotopic techniques. Here we show that accurate U-Pb isotopic analysis of nanoscale domains of baddeleyite can be achieved by atom probe tomography. Within individual crystals of highly shocked baddeleyite from the Sudbury impact structure, three discrete nanostructural domains have been isolated yielding average 206Pb/238U ages of 2,436±94 Ma (protolith crystallization) from homogenous-Fe domains, 1,852±45 Ma (impact) from clustered-Fe domains and 1,412±56 Ma (tectonic metamorphism) from planar and subgrain boundary structures. Baddeleyite is a common phase in terrestrial, Martian, Lunar and asteroidal materials, meaning this atomic-scale approach holds great potential in establishing a more accurate chronology of the formation and evolution of planetary crusts.

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The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations ∼2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rod-shaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

22 23 A first step to understanding the initial conditions for habitability pathways 24 in planetary systems is to determine when heavy meteorite bombardments waned 25 and the earliest crust remained below the known thermal and shock pressure 26 limits on microbiota survival (121°C, 78 GPa). We have determined this timing on Mars by documenting the metamorphic histories of its oldest known, 4.476 Ga to 4.430 Ga, grains of the highly resilient minerals zircon and baddeleyite in the Rabt Sbayta polymict breccia meteorites; crustal fragments of the southern highlands. Here we show using electron and atom probe microscopy that the Mars grains (n=121) have all remained beneath 78 GPa conditions, with 97% exhibiting weak to no shock metamorphic features, or thermal overprints due to shock-induced melting and magmatism. This is opposite to bombarded crust on Earth and Moon wherein ~80% of grains show such features. The nearly pristine state of the Mars minerals thus establishes a lower age bracket of 4.48 Ga for the planet-scale impact that created the hemispheric dichotomy, and obviates any later cataclysmic bombardments. Considering existing thermal habitability models, portions of early Mars crust reached habitable conditions by at least 4.2 Ga, the onset of the martian 'wet' period, as much as ~500 million years earlier than the earliest record of life on Earth. An early giant impact period on Mars, broadly coeval with Moon formation, may have heralded early abiogenesis on both planets.

Accurately constraining the formation and evolution of the lunar magnesian (Mg) suite is key to understanding the earliest periods of magmatic crustal building that followed accretion and primordial differentiation of the Moon. However, the origin and evolution of these unique rocks is highly debated. Here, we report on the microstructural characterisation of a large (~250 µm) baddeleyite (monoclinic-ZrO2) grain in Apollo troctolite 76535 that preserves quantifiable crystallographic relationships indicative of reversion from a precursor cubic-ZrO2 phase. This observation places important constraints on the formation temperature of the grain (> 2300 °C) which endogenic processes alone fail to reconcile. We conclude that the troctolite crystallized directly from a large, differentiated impact melt sheet 4326 ± 14 million years (Myr) ago. These results suggest that impact bombardment would have played a critical role in the evolution of the earliest planetary crusts. Insights into the formation, differentiation and impact bombardment of planetary bodies have been derived through geodynamic modelling, remote sensing observations, and isotopic analysis of planetary meteorites and returned samples. The resulting models are hindered by the paucity of mineralogical evidence that can place direct constraints on these very high temperature and pressure processes. Although many mineral thermobarometers can record geological temperatures ranging up to a maximum of ~1500 °C, empirical mineralogical and geochemical evidence of higher temperatures is often lost due to extensive