Jihua Hao

Water oceans in large icy moons and exoplanets are isolated from the rocky interior by thick layers of high-pressure ice, which hinder the direct release of nutrients and organics derived from water-rock interaction to the ocean. Possible uptake of these bio-essential compounds into high-pressure ice phases could regulate their availability in the ocean, but this process is poorly constrained. Here, we measured partition coefficients of glycine and alanine into ices VI and VII under elevated temperature-pressure conditions using a diamond-anvil cell. We observed moderate compatibility of glycine and alanine with partition coefficients: K _{p ,glycine} = 0.14 and 0.40 in ices VI and VII, respectively; K _{p ,alanine} = 0.21 and 0.35 in ices VI and VII, respectively. First-principles calculations suggested that amino acids could be incorporated into high-pressure ice’s lattice via cogrowth. Compatibility of amino acids into high-pressure ices would favor their transport in large extraterrestrial oceans, opening an avenue to habitability.

Liquid water exists on the Earth and several other planetary bodies in our solar system. The chemical character of these aqueous reservoirs is central to evaluating their habitability. Here, we synthesize the chemical features of water reservoirs and their biological implications on the modern Earth. We then outline constraints on the evolutionary history of Earth's ocean chemistry and discuss its interplay with the biosphere. Furthermore, we examine the inferred chemical environments of water bodies on early Mars, dwarf planet Ceres, Jupiter's moon Europa and Saturn's moons Enceladus and Titan. We conclude by outlining priority questions for future planetary habitability studies.

Manganese oxides, thought to form almost exclusively through reactions between Mn ²⁺ and O ₂ , catalyze oxidative transformations among redox-sensitive metals. Thus, the occurrence of Mn oxides, either observed or inferred from sedimentary geochemical data, has formed the basis for multiple hypotheses concerning the evolution of the atmospheric redox state on the early Earth and Mars. Here, using theory and experiments, we report that the band gap of common Ca/Mg carbonate minerals (including calcite, magnesite, and aragonite) is significantly lowered by trace incorporation (0.8 wt% or lower) of Mn(II) into their bulk structure or surface, conferring photochemical reactivity under ultraviolet conditions relevant to early Earth and Mars (200 to 400 nm). Moreover, we show that surface incorporation of Mn(II) reduces the fundamental band gap much more effectively (by >1 eV) than bulk incorporation. Our results suggest that photo-oxidation of Mn(II)-bearing carbonates could have occurred widely on planetary surfaces, resulting in the abiotic formation of manganese oxides without free molecular oxygen. Photochemically driven redox cycling of manganese could help sustain redox disequilibria for microbial metabolisms, but compromises the use of manganese oxides as oxygen barometers.

The accumulation of free oxygen in the atmosphere ≈2.45 billion years ago was one of the most transformative events in Earth’s past. Since its identification, this interval termed the ‘Great Oxidation Event’ (GOE), has garnered a large amount of attention from a wide array of perspectives, with some suggesting it should define its own geologic era or period. Despite many new tools to interrogate the GOE, today the defendable range of possible atmospheric O₂ levels span orders of magnitude, begging the question, how great was Earth’s Great Oxidation? The consequences of such disparate views on oxygenation levels are uncertainties regarding biospheric evolution, interpretations of the sedimentary record, and a limited ability to translate Earth’s atmospheric history into insights for exoplanet research. In this review, we revisit the conditions immediately before, during, and after Earth’s GOE to explore the key assumptions that underlie differing views on this critical interval of time. We then highlight new discoveries and outline extremely divergent but defendable interpretations of atmospheric oxygen trajectories across the GOE. Reducing such divergent scenarios should be a major target of research progress in the coming years.

Geoelectrochemical reduction of CO₂ is proposed as a potentially significant abiotic synthesis pathway catalyzed by sulfide minerals under planetary conditions, but whether this reaction could be catalyzed by geologically abundant carbonate and phyllosilicate minerals is unknown. Here we show that adsorption of trace transition metal cations, such as Cu(II) and Zn(II), endows common Ca/Mg-carbonates and phyllosilicates with high catalytic performance for CO₂ reduction to form methane, formic acid, carbon monoxide, and C₂ organics. We also observe viable synthesis of C-N bonded compounds (mainly acetamide) when ammonia is present. During these reactions, the adsorbed metal cations are partially reduced into metallic states and become catalytic, while mineral substrates facilitate the water dissociation to supply protons for CO₂ hydrogenation. This facile electrochemical reduction of CO₂ catalyzed by carbonates and phyllosilicates could facilitate the origin of life on the primitive Earth and help explain the detection of organics on other habitable planetary bodies.

The phosphorus (P) cycle links the co-evolution of the biosphere and geosphere over geologic time. Modern P availability is primarily controlled by mineral adsorption, but how such processes might have operated under early Earth’s anoxic conditions remains unclear. Here, we combine experimental and theoretical investigations of P adsorption onto common phyllosilicates to evaluate their role in the early P cycle. We show that the P adsorption would have been significantly enhanced in early ferruginous waters, primarily through dissolved Fe(II) bridging between orthophosphate and mineral surfaces. Such enhanced P adsorption onto phyllosilicates could have facilitated the riverine transport of bioavailable P during Archean anoxic continental weathering, yet also promoted its rapid burial in shallow marine settings. Moreover, phyllosilicate adsorption would have limited dissolved P release during seafloor weathering in the Archean and Proterozoic oceans. These processes collectively could have limited dissolved P availability for the origin and evolution of early life.