The oxidation state of Hadean magmas and implications for early Earth’s atmosphere

Atomically Resolved Transition Pathways of Iron Redox

The redox transition between iron and its oxides is of the utmost importance in heterogeneous catalysis, biological metabolism, and geological evolution. The structural characteristics of this reaction may vary based on surrounding environmental conditions, giving rise to diverse physical scenarios. In this study, we explore the atomic-scale transformation of nanosized Fe3O4 under ambient-pressure H2 gas using in-situ environmental transmission electron microscopy. Our results reveal that the internal solid-state reactions dominated by iron diffusion are coupled with the surface reactions involving gaseous O or H species. During reduction, we observe two competitive reduction pathways, namely Fe3O4 → FeO → Fe and Fe3O4 → Fe. An intermediate phase with vacancy ordering is observed during the disproportionation reaction of Fe2+ → Fe0 + Fe3+, which potentially alleviates stress and facilitates ion migration. As the temperature decreases, an oxidation process occurs in the presence of environmental H2O and trace amounts of O2. A direct oxidation of Fe to Fe3O4 occurs in the absence of the FeO phase, likely corresponding to a change in the water vapor content in the atmosphere. This work elucidates a full dynamical scenario of iron redox under realistic conditions, which is critical for unraveling the intricate mechanisms governing the solid-solid and solid-gas reactions.

Europium in plagioclase-hosted melt inclusions reveals mantle melting modulates oxygen fugacity

To gain insights into the composition and heterogeneity of Earth's interior, the partial pressure of oxygen (oxygen fugacity, or fO2) in igneous rocks is characterized. A surprising observation is that relative to reference buffers, fO2s of mantle melts (mid-ocean ridge basalts, or MORBs) and their presumed mantle sources (abyssal peridotites) differ. Globally, MORBs have near-uniform fO2s, whereas abyssal peridotites vary by about three orders of magnitude, suggesting these intimately related geologic reservoirs are out of equilibrium. Here, we characterize fO2s of mantle melting increments represented by plagioclase-hosted melt inclusions, which were entrapped as basaltic melts migrated from their sources toward the seafloor. At temperatures and fO2s constrained by rare earth element distributions, a range of fO2s consistent with the abyssal peridotites is recovered. The fO2s are correlated with geochemical proxies for mantle melting, suggesting partial melting of Earth's mantle decreases its fO2, and that the uniformity of MORB fO2s is a consequence of the melting process and plate tectonic cycling.

Chapter 4: A Geological and Chemical Context for the Origins of Life on Early Earth

Within the first billion years of Earth's history, the planet transformed from a hot, barren, and inhospitable landscape to an environment conducive to the emergence and persistence of life. This chapter will review the state of knowledge concerning early Earth's (Hadean/Eoarchean) geochemical environment, including the origin and composition of the planet's moon, crust, oceans, atmosphere, and organic content. It will also discuss abiotic geochemical cycling of the CHONPS elements and how these species could have been converted to biologically relevant building blocks, polymers, and chemical networks. Proposed environments for abiogenesis events are also described and evaluated. An understanding of the geochemical processes under which life may have emerged can better inform our assessment of the habitability of other worlds, the potential complexity that abiotic chemistry can achieve (which has implications for putative biosignatures), and the possibility for biochemistries that are vastly different from those on Earth.

Oxidation of iron by giant impact and its implication on the formation of reduced atmosphere in the early Earth

Giant impact-driven redox processes in the atmosphere and magma ocean played crucial roles in the evolution of Earth. However, because of the absence of rock records from that time, understanding these processes has proven challenging. Here, we present experimental results that simulate the giant impact-driven reactions between iron and volatiles (H2O and CO2) using x-ray free electron laser (XFEL) as fast heat pump and structural probe. Under XFEL pump, iron is oxidized to wüstite (FeO), while volatiles are reduced to H2 and CO. Furthermore, iron oxidation proceeds into formation of hydrides (γ-FeHx) and siderite (FeCO3), implying redox boundary near 300-km depth. Through quantitative analysis on reaction products, we estimate the volatile and FeO budgets in bulk silicate Earth, supporting the Theia hypothesis. Our findings shed light on the fast and short-lived process that led to reduced atmosphere, required for the emergence of prebiotic organic molecules in the early Earth.

The Moon-Forming Impact and the Autotrophic Origin of Life

The Moon-forming impact vaporized part of Earth's mantle, and turned the rest into a magma ocean, from which carbon dioxide degassed into the atmosphere, where it stayed until water rained out to form the oceans. The rain dissolved CO2 and made it available to react with transition metal catalysts in the Earth's crust so as to ultimately generate the organic compounds that form the backbone of microbial metabolism. The Moon-forming impact was key in building a planet with the capacity to generate life in that it converted carbon on Earth into a homogeneous and accessible substrate for organic synthesis. Today all ecosystems, without exception, depend upon primary producers, organisms that fix CO2 . According to theories of autotrophic origin, it has always been that way, because autotrophic theories posit that the first forms of life generated all the molecules needed to build a cell from CO2 , forging a direct line of continuity between Earth's initial CO2 -rich atmosphere and the first microorganisms. By modern accounts these were chemolithoautotrophic archaea and bacteria that initially colonized the crust and still inhabit that environment today.

Significant impact of redox regulation of estrogen-metabolizing proteins on cellular stress responses

The ultimate driving force, stress, promotes adaptability/evolution in proliferating organisms, transforming tumorigenic growth. Estradiol (E2) regulates both phenomena. In this study, bioinformatics-tools, site-directed-mutagenesis (human estrogen-sulfotransferase/hSULT1E1), HepG2 cells tested with N-acetyl-cysteine (NAC/thiol-inducer) or buthionine-sulfoxamine (BSO/thiol-depletory) were evaluated for hSULT1E1 (estradiol-sulphating/inactivating) functions. Reciprocal redox regulation of steroid sulfatase (STS, E2-desulfating/activating) results in the Cys-formylglycine transition by the formylglycine-forming enzyme (FGE). The enzyme sequences and structures were examined across the phylogeny. Motif/domain and the catalytic conserve sequences and protein-surface-topography (CASTp) were investigated. The E2 binding to SULT1E1 suggests that the conserved-catalytic-domain in this enzyme has critical Cysteine 83 at position. This is strongly supported by site-directed mutagenesis/HepG2-cell research. Molecular-docking and superimposition studies of E2 with the SULT1E1 of representative species and to STS reinforce this hypothesis. SULT1E1-STS are reciprocally activated in response to the cellular-redox-environment by the critical Cys of these two enzymes. The importance of E2 in organism/species proliferation and tissue tumorigenesis is highlighted.

Evaluating the abiotic synthesis potential and the stability of building blocks of life beneath an impact-induced steam atmosphere

A prerequisite for prebiotic chemistry is the accumulation of critical building blocks of life. Some studies argue that more frequent impact events on the primitive Earth could have induced a more reducing steam atmosphere and thus favor widespread and more efficient synthesis of life building blocks. However, elevated temperature is also proposed to threaten the stability of organics and whether life building blocks could accumulate to appreciable levels in the reducing yet hot surface seawater beneath the steam atmosphere is still poorly examined. Here, we used a thermodynamic tool to examine the synthesis affinity of various life building blocks using inorganic gasses as reactants at elevated temperatures and corresponding steam pressures relevant with the steam-seawater interface. Our calculations show that although the synthesis affinity of all life building blocks decreases when temperature increases, many organics, including methane, methanol, and carboxylic acids, have positive synthesis affinity over a wide range of temperatures, implying that these species were favorable to form (>10-6 molal) in the surface seawater. However, cyanide and formaldehyde have overall negative affinities, suggesting that these critical compounds would tend to undergo hydrolysis in the surface seawaters. Most of the 18 investigated amino acids have positive affinities at temperature <220°C and their synthesis affinity increases under more alkaline conditions. Sugars, ribose, and nucleobases have overall negative synthesis affinities at the investigated range of temperatures. Synthesis affinities are shown to be sensitive to the hydrogen fugacity. Higher hydrogen fugacity (in equilibrium with FQI or IW) favors the synthesis and accumulation of nearly all the investigated compounds, except for HCN and its derivate products. In summary, our results suggest that reducing conditions induced by primitive impacts could indeed favor the synthesis/accumulation of some life building blocks, but some critical species, particularly HCN and nucleosides, were still unfavorable to accumulate to appreciable levels. Our results can provide helpful guidance for future efforts to search for or understand the stability of biomolecules on other planets like Mars and icy moons. We advocate examining craters formed by more reducing impactors to look for the preservation of prebiotic materials.

Dynamic Environmental Conditions Affect the Composition of a Model Prebiotic Reaction Network

Prebiotic environments are dynamic, containing a range of periodic and aperiodic variations in reaction conditions. However, the impact of the temporal dynamics of environmental conditions upon prebiotic chemical reaction networks has not been investigated. Here, we demonstrate how the magnitude and rate of temporal fluctuations of the catalysts Ca²⁺ and hydroxide control the product distributions of the formose reaction. Surprisingly, the product compositions of the formose reaction under dynamic conditions deviate significantly from those under steady state conditions. We attribute these compositional changes to the non-uniform propagation of fluctuations through the network, thereby shaping reaction outcomes. An examination of temporal concentration patterns showed that collections of compounds responded collectively to perturbations, indicating that key gating reactions branching from the Breslow cycle may be important responsive features of the formose reaction. Our findings show how the compositions of prebiotic reaction networks were shaped by sequential environmental events, illustrating the necessity for considering the temporal traits of prebiotic environments that supported the origin of life.

Phosphorylation in liquid sulfur dioxide under prebiotically plausible conditions

In nature, organophosphates provide key functions such as information storage and transport, structural tasks, and energy transfer. Since condensations are unfavourable in water and nucleophilic attack at phosphate is kinetically inhibited, various abiogenesis hypotheses for the formation of organophosphate are discussed. Recently, the application of phosphites as phosphorylation agent showed promising results. However, elevated temperatures and additional reaction steps are required to obtain organophosphates. Here we show that in liquid sulfur dioxide, which acts as solvent and oxidant, efficient organophosphate formation is enabled. Phosphorous acid yields up to 32.6% 5' nucleoside monophosphate, 3.6% 5' nucleoside diphosphate, and the formation of nucleoside triphosphates and dinucleotides in a single reaction step at room temperature. In addition to the phosphorylation of organic compounds, we observed diserine formation. Thus, we suggest volcanic environments as reaction sites for biopolymer formation on Early Earth. Because of the simple recyclability of sulfur dioxide, the reaction is also interesting for synthesis chemistry.

Azoles as Auxiliaries and Intermediates in Prebiotic Nucleoside Synthesis

4,5-Dicyanoimidazole and 2-aminothiazole are azoles that have previously been implicated in prebiotic nucleotide synthesis. The former compound is a byproduct of adenine synthesis, and the latter compound has been shown to be capable of separating C₂ and C₃ sugars via crystallization as their aminals. We now report that the elusive intermediate cyanoacetylene can be captured by 4,5-dicyanoimidazole and accumulated as the crystalline compound N-cyanovinyl-4,5-dicyanoimidazole, thus providing a solution to the problem of concentration of atmospherically formed cyanoacetylene. Importantly, this intermediate is a competent cyanoacetylene surrogate, reacting with ribo-aminooxazoline in formamide to give ribo-anhydrocytidine ─ an intermediate in the divergent synthesis of purine and pyrimidine nucleotides. We also report a prebiotically plausible synthesis of 2-aminothiazole and examine the mechanism of its formation. The utilization of each of these azoles enhances the prebiotic synthesis of ribonucleotides, while their syntheses comport with the cyanosulfidic scenario we have previously described.

A global network model of abiotic phosphorus cycling on Earth through time

Phosphorus (P) is a crucial structural component of living systems and central to modern bioenergetics. P cycles through terrestrial geochemical reservoirs via complex physical and chemical processes. Terrestrial life has altered these fluxes between reservoirs as it evolved, which is why it is of interest to explore planetary P flux evolution in the absence of biology. This is especially true, since environmental P availability affects life’s ability to alter other geochemical cycles, which could then be an example of niche construction. Understanding how P reservoir transport affects environmental P availability helps parameterize how the evolution of P reservoirs influenced the emergence of life on Earth, and potentially other planetary bodies. Geochemical P fluxes likely change as planets evolve, and element cycling models that take those changes into account can provide insights on how P fluxes evolve abiotically. There is considerable uncertainty in many aspects of modern and historical global P cycling, including Earth’s initial P endowment and distribution after core formation and how terrestrial P interactions between reservoirs and fluxes and their rates have evolved over time. We present here a dynamical box model for Earth’s abiological P reservoir and flux evolution. This model suggests that in the absence of biology, long term planetary geochemical cycling on planets similar to Earth with respect to geodynamism tends to bring P to surface reservoirs, and biology, including human civilization, tends to move P to subductable marine reservoirs.

A Review of the "Black Beauty" Martian Regolith Breccia and Its Martian Habitability Record

The regolith breccia Northwest Africa (NWA) 7034 and paired samples are unique meteorite representatives of the martian crust. They are water rich, lithologically varied, and preserve the oldest martian zircon grains yet discovered that formed ca. 4500-4300 Ma. The meteorite thus provides us with an invaluable record of the crustal and environmental conditions on early Mars. Resetting of some radioisotopic chronometers occurred in response to a major thermal disturbance event ca. 1500-1400 Ma, likely caused by an impactor that brecciated and redeposited NWA 7034 near the surface in an ejecta blanket. Lithologies comprising NWA 7034 were then aqueously altered by a long-lasting impact-induced hydrothermal system, before being excavated and ejected by a subsequent impact at ca. 5-15 Ma. This review compiles chronological and petrological information into an overarching geochronological summary for NWA 7034 and paired samples. We then provide a synopsis for the volatile (H₂O, C) inventory and hydrothermal alteration history of NWA 7034. From this geochronological history and volatile inventory, we interpret and assess two potential periods of martian habitability: (1) an early window of pre-Noachian planetary habitability, and (2) impact-derived hydrothermal systems that allowed intermittent habitable crater environments well into the Amazonian.

Catalytic Synthesis of Polyribonucleic Acid on Prebiotic Rock Glasses

Reported here are experiments that show that ribonucleoside triphosphates are converted to polyribonucleic acid when incubated with rock glasses similar to those likely present 4.3-4.4 billion years ago on the Hadean Earth surface, where they were formed by impacts and volcanism. This polyribonucleic acid averages 100-300 nucleotides in length, with a substantial fraction of 3',-5'-dinucleotide linkages. Chemical analyses, including classical methods that were used to prove the structure of natural RNA, establish a polyribonucleic acid structure for these products. The polyribonucleic acid accumulated and was stable for months, with a synthesis rate of 2 × 10^-3 pmoles of triphosphate polymerized each hour per gram of glass (25°C, pH 7.5). These results suggest that polyribonucleotides were available to Hadean environments if triphosphates were. As many proposals are emerging describing how triphosphates might have been made on the Hadean Earth, the process observed here offers an important missing step in models for the prebiotic synthesis of RNA.

Carbon dioxide photoreduction in prebiotic environments

The reduction of carbon dioxide is one of the hottest topics due to the concern of global warming. Carbon dioxide reduction is also an essential step for life's origins as photoautotrophs arose soon after Earth formation. Both the topics are of high general interest, and possibly, there could be a fruitful cross-fertilization of the two fields. Herein, we selected and collected papers related to photoreduction of carbon dioxide using compounds easily available on the Earth and considered of prebiotic relevance. This work might be useful also to scientists interested in carbon dioxide photoreduction and/or to have an overview of the techniques available.

Planetary Minerals Catalyze Conversion of a Polycyclic Aromatic Hydrocarbon to a Prebiotic Quinone: Implications for Origins of Life

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in astrochemical environments and are disbursed into planetary environments via meteorites and extraterrestrial infall where they may interact with mineral phases to produce quinones important for origins of life. In this study, we assessed the potential of the phyllosilicates montmorillonite (MONT) and kaolinite (KAO), and the enhanced Mojave Mars Simulant (MMS) to convert the PAH anthracene (ANTH) to the biologically important 9,10-anthraquinone (ANTHQ). All studied mineral substrates mediate conversion over the temperature range assessed (25-500°C). Apparent rate curves for conversion were sigmoidal for MONT and KAO, but quadratic for MMS. Conversion efficiency maxima for ANTHQ were 3.06% ± 0.42%, 1.15% ± 0.13%, and 0.56% ± 0.039% for MONT, KAO, and MMS, respectively. We hypothesized that differential substrate binding and compound loss account for the apparent conversion kinetics observed. Apparent loss rate curves for ANTH and ANTHQ were exponential for all substrates, suggesting a pathway for wide distribution of both compounds in warmer prebiotic environments. These findings improve upon our previously reported ANTHQ conversion efficiency on MONT and provide support for a plausible scenario in which PAH-mineral interactions could have produced prebiotically relevant quinones in early Earth environments.

The automatic parameter-exploration with a machine-learning-like approach: Powering the evolutionary modeling on the origin of life

The origin of life involved complicated evolutionary processes. Computer modeling is a promising way to reveal relevant mechanisms. However, due to the limitation of our knowledge on prebiotic chemistry, it is usually difficult to justify parameter-setting for the modeling. Thus, typically, the studies were conducted in a reverse way: the parameter-space was explored to find those parameter values “supporting” a hypothetical scene (that is, leaving the parameter-justification a later job when sufficient knowledge is available). Exploring the parameter-space manually is an arduous job (especially when the modeling becomes complicated) and additionally, difficult to characterize as regular “Methods” in a paper. Here we show that a machine-learning-like approach may be adopted, automatically optimizing the parameters. With this efficient parameter-exploring approach, the evolutionary modeling on the origin of life would become much more powerful. In particular, based on this, it is expected that more near-reality (complex) models could be introduced, and thereby theoretical research would be more tightly associated with experimental investigation in this field–hopefully leading to significant steps forward in respect to our understanding on the origin of life.

People have long been interested in the evolutionary processes through which life on our planet could have arisen from a non-life background. However, it seems that experimental studies in this field are proceeding slowly, perhaps owing to the complication of such processes. In the meantime, computer modeling has shown its potential to disclose the evolutionary mechanisms involved. Now a major difficulty of the computer modeling work is to justify the parameter-setting–on account of our limited knowledge on prebiotic chemistry and environments. Thus, people tend to explore the parameter space to seek parameter values in favor of the hypothetic scene and leave the parameter-justification a later job when sufficient knowledge is available. To date, the parameter-exploration is usually conducted manually (in many cases by trial and error), thus arduous and unpredictable. Inspired by the algorithm of machine-learning, we designed an automatic approach of parameter-exploration. The results showed that the approach is quite effective–that is, “good” parameter-sets in favor of hypothetic scenes in the origin of life can be found automatically. It is expected that such a machine-learning-like method would greatly enhance the efficiency of our evolutionary modeling studies on the origin of life in future.

Apatite and Zircon Geochemistry in Yao’an Alkali-Rich Porphyry Gold Deposit, Southwest China: Implications for Petrogenesis and Mineralization

The Yao’an gold deposit is located in the middle of the Jinshajiang-Ailaoshan alkali-rich metallogenic belt, and this belt hosts many porphyry-type Cu-Au-Mo deposits formed at 46–33 Ma. Yao’an porphyry gold-mineralization is intimately associated with biotite syenite porphyry, whereas the contemporaneous quartz syenite porphyry is barren. In this study, we compared the major and trace elements of apatite and zircon and isotopic compositions of zircon from the biotite syenite porphyry and quartz syenite porphyry, to explore their geochemical differences that may affect their mineralization potential. The results show that both porphyries were derived from the partial melting of the thickened lower crust, which has been modified by slab-derived fluids, but has different mineral crystallization sequences, magma fluid activities, and magma oxidation states, respectively. REE contents in apatite and zircon can be used to reveal the crystallization sequence of minerals. A rapid decrease of (La/Yb)N ratio in apatite from both porphyries may be caused by the crystallization of allanite. Large variation of Cl contents and negative correlation between F/Cl and (La/Yb)N in apatite from fertile porphyry indicate that it has experienced the exsolution of Cl-bearing hydrothermal fluid. Higher Y/Ho and lower Zr/Hf in zircon from fertile porphyry indicate a stronger fluid activity than barren porphyry. The high S, V, As contents, δEu, low δCe in apatite, as well as high Ce4+/Ce3+ and log(fO2) estimated from zircon geochemistry from fertile porphyry, indicate high a oxidation state of fertile porphyry, similar to other fertile porphyries in this metallogenic belt. High fluid activity and fluid exsolution are conducive to the migration and enrichment of metal elements, which are very important for mineralization. High oxygen fugacity inhibits the precipitation of metal in the form of sulfide, thereby enhancing the mineralization potential of rock. Therefore, the exsolution of Cl-bearing hydrothermal fluid and high oxygen fugacity are the key factors promoting mineralization in Yao’an area.

The role of borosilicate glass in Miller-Urey experiment

We have designed a set of experiments to test the role of borosilicate reactor on the yielding of the Miller-Urey type of experiment. Two experiments were performed in borosilicate flasks, two in a Teflon flask and the third couple in a Teflon flask with pieces of borosilicate submerged in the water. The experiments were performed in CH4, N2, and NH3 atmosphere either buffered at pH 8.7 with NH4Cl or unbuffered solutions at pH ca. 11, at room temperature. The Gas Chromatography-Mass Spectroscopy results show important differences in the yields, the number of products, and molecular weight. In particular, a dipeptide, multi-carbon dicarboxylic acids, PAHs, and a complete panel of biological nucleobases form more efficiently or exclusively in the borosilicate vessel. Our results offer a better explanation of the famous Miller's experiment showing the efficiency of borosilicate in a triphasic system including water and the reduced Miller-Urey atmosphere.

The "Water Problem"(sic), the Illusory Pond and Life's Submarine Emergence-A Review

The assumption that there was a "water problem" at the emergence of life-that the Hadean Ocean was simply too wet and salty for life to have emerged in it-is here subjected to geological and experimental reality checks. The "warm little pond" that would take the place of the submarine alkaline vent theory (AVT), as recently extolled in the journal Nature, flies in the face of decades of geological, microbiological and evolutionary research and reasoning. To the present author, the evidence refuting the warm little pond scheme is overwhelming given the facts that (i) the early Earth was a water world, (ii) its all-enveloping ocean was never less than 4 km deep, (iii) there were no figurative "Icelands" or "Hawaiis", nor even an "Ontong Java" then because (iv) the solidifying magma ocean beneath was still too mushy to support such salient loadings on the oceanic crust. In place of the supposed warm little pond, we offer a well-protected mineral mound precipitated at a submarine alkaline vent as life's womb: in place of lipid membranes, we suggest peptides; we replace poisonous cyanide with ammonium and hydrazine; instead of deleterious radiation we have the appropriate life-giving redox and pH disequilibria; and in place of messy chemistry we offer the potential for life's emergence from the simplest of geochemically available molecules and ions focused at a submarine alkaline vent in the Hadean-specifically within the nano-confined flexible and redox active interlayer walls of the mixed-valent double layer oxyhydroxide mineral, fougerite/green rust comprising much of that mound.

Composition of the Primordial Ocean Just after Its Formation: Constraints from the Reactions between the Primitive Crust and a Strongly Acidic, CO2-Rich Fluid at Elevated Temperatures and Pressures

The Hadean was an enigmatic period in the Earth’s history when ocean formation and the emergence of life may have occurred. However, minimal geological evidence is left from this period. To understand the primordial ocean’s composition, we focused on the ocean’s formation processes from CO2- and HCl-bearing water vapor in the high-temperature atmosphere. When the temperature of the lower atmosphere fell below the critical point, high-temperature rain reached the ground surface. Then, hydrothermal reactions between the subcritical fluid and primordial crust started. Eventually, a liquid ocean emerged on the completely altered crust as the temperature decreased to approximately 25 °C. Here, we conducted two experiments and modeling to simulate the reactions of hypothetical primordial crustal rock (basalt or komatiite). The results indicate that the primordial ocean was mildly acidic and rich in CO2, Mg, and Ca relative to Na, irrespective of the rock type, which is different from the modern equivalents. Therefore, unlike the present seawater, the primordial seawater could have been carbonic, bitter, and harsh rather than salty.

Experimental Investigation of the Formation of Formaldehyde by Hadean and Noachian Impacts

Formaldehyde (FA) is an important precursor in the abiotic synthesis of major biomolecules including amino acids, sugars, and nucleobases. Thus, spontaneous formation of prebiotic FA must have been crucial for the chemical origin of life. The frequent impacts of meteorites and asteroids on Hadean Earth have been considered one of the abiotic synthetic processes of organic compounds. However, the impact-induced formation of FA from CO₂ as the major atmospheric constituent has not been confirmed yet. This study investigated the formation of FA in impact-induced reactions among meteoritic minerals, bicarbonate, gaseous nitrogen, and water to simulate the abiotic process experimentally. Products were analyzed with ultra-high-performance liquid chromatography/tandem mass spectrometry and powder X-ray diffraction techniques. The results show the formation of FA and oxidation of metallic iron to siderite in the impact shock experiments. This indicates that this important prebiotic molecule was also synthesized by impacts of iron-bearing meteorites/asteroids on the Hadean oceans. The impact events might have generated spatially and temporally FA-enriched localized environments. Moreover, the impact-induced synthesis of FA may have also occurred on Noachian Mars given the presence of liquid water and a CO₂-N₂-rich atmosphere on the planet.

Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth

When hydrated, phosphides such as the mineral schreibersite, (Fe,Ni)₃P, allow for the synthesis of important phosphorus-bearing organic compounds. Such phosphides are common accessory minerals in meteorites; consequently, meteorites are proposed to be a main source of prebiotic reactive phosphorus on early Earth. Here, we propose an alternative source for widespread phosphorus reduction, arguing that lightning strikes on early Earth potentially formed 10-1000 kg of phosphide and 100-10,000 kg of phosphite and hypophosphite annually. Therefore, lightning could have been a significant source of prebiotic, reactive phosphorus which would have been concentrated on landmasses in tropical regions. Lightning strikes could likewise provide a continual source of prebiotic reactive phosphorus independent of meteorite flux on other Earth-like planets, potentially facilitating the emergence of terrestrial life indefinitely.

Abiotic Synthesis of Nucleoside 5'-Triphosphates with Nickel Borate and Cyclic Trimetaphosphate (CTMP)

While nucleoside 5'-triphosphates are precursors for RNA in modern biology, the presumed difficulty of making these triphosphates on Hadean Earth has caused many prebiotic researchers to consider other activated species for the prebiotic synthesis of RNA. We report here that nickel(II), in the presence of borate, gives substantial amounts (2-3%) of nucleoside 5'-triphosphates upon evaporative heating in the presence of urea, salts, and cyclic trimetaphosphate (CTMP). Also recovered are nucleoside 5'-diphosphates and nucleoside 5'-monophosphates, both likely arising from 5'-triphosphate intermediates. The total level of 5'-phosphorylation is typically 30%. Borate enhances the regiospecificity of phosphorylation, with increased amounts of other phosphorylated species seen in its absence. Experimentally supported paths are already available to make nucleosides in environments likely to have been present on Hadean Earth soon after a midsized 10²¹ to 10²³ kg impactor, which would also have delivered nickel to the Hadean surface. Further, sources of prebiotic CTMP continue to be proposed. Thus, these results fill in one of the few remaining steps needed to demystify the prebiotic synthesis of RNA and support a continuous model from atmospheric components to oligomeric RNA that is lacking only a mechanism to obtain homochirality in the product RNA.

Dissipation-driven selection of states in non-equilibrium chemical networks

Life has most likely originated as a consequence of processes taking place in non-equilibrium conditions (e.g. in the proximity of deep-sea thermal vents) selecting states of matter that would have been otherwise unfavorable at equilibrium. Here we present a simple chemical network in which the selection of states is driven by the thermodynamic necessity of dissipating heat as rapidly as possible in the presence of a thermal gradient: states participating to faster reactions contribute the most to the dissipation rate, and are the most populated ones in non-equilibrium steady-state conditions. Building upon these results, we show that, as the complexity of the chemical network increases, the velocity of the reaction path leading to a given state determines its selection, giving rise to non-trivial localization phenomena in state space. A byproduct of our studies is that, in the presence of a temperature gradient, thermophoresis-like behavior inevitably appears depending on the transport properties of each individual state, thus hinting at a possible microscopic explanation of this intriguing yet still not fully understood phenomenon.

Atmospheric Nitrogen When Life Evolved on Earth

The amount of nitrogen (N₂) present in the atmosphere when life evolved on our planet is central for understanding the production of prebiotic molecules and, hence, is a fundamental quantity to constrain. Estimates of atmospheric molecular nitrogen partial surface pressures during the Archean, however, widely vary in the literature. In this study, we apply a model that combines newly gained insights into atmospheric escape, magma ocean duration, and outgassing evolution. Results suggest <420 mbar surface molecular nitrogen at the time when life originated, which is much lower compared with estimates in previous works and hence could impact our understanding of the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments that simulate prebiotic chemistry on the early Earth. Our results that assume negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gyr ago, which suggest that the atmospheric pressure was probably less than half the present-day value. Our results contradict previous studies that assume N₂ partial surface pressures during the Archean were higher than those observed today and suggest that, if the N₂ partial pressure were low in the Archean, it would likely be low in the Hadean as well. Furthermore, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N₂ per year (Tg N₂/year), which is consistent with modern marine biofixation rates and, hence, indicate an oceanic origin of this fixation process.

One-Pot Hydrogen Cyanide-Based Prebiotic Synthesis of Canonical Nucleobases and Glycine Initiated by High-Velocity Impacts on Early Earth

Chemical environments of young planets are assumed to be significantly influenced by impacts of bodies lingering after the dissolution of the protoplanetary disk. We explore the chemical consequences of impacts of these bodies under reducing planetary atmospheres dominated by carbon monoxide, methane, and molecular nitrogen. Impacts were simulated by using a terawatt high-power laser system. Our experimental results show that one-pot impact-plasma-initiated synthesis of all the RNA canonical nucleobases and the simplest amino acid glycine is possible in this type of atmosphere in the presence of montmorillonite. This one-pot synthesis begins with de novo formation of hydrogen cyanide (HCN) and proceeds through intermediates such as cyanoacetylene and urea.

Prebiotic Nucleoside Synthesis: The Selectivity of Simplicity

Ever since the discovery of nucleic acids 150 years ago,[1] major achievements have been made in understanding and decrypting the fascinating scientific questions of the genetic code.[2] However, the most fundamental question about the origin and the evolution of the genetic code remains a mystery. How did nature manage to build up such intriguingly complex molecules able to encode structure and function from simple building blocks? What conditions were required? How could the precursors survive the unhostile environment of early Earth? Over the past decades, promising synthetic concepts were proposed providing clarity in the field of prebiotic nucleic acid research. In this Minireview, we show the current status and various approaches to answer these fascinating questions.

Six 'Must-Have' Minerals for Life's Emergence: Olivine, Pyrrhotite, Bridgmanite, Serpentine, Fougerite and Mackinawite

Life cannot emerge on a planet or moon without the appropriate electrochemical disequilibria and the minerals that mediate energy-dissipative processes. Here, it is argued that four minerals, olivine ([Mg>Fe]2SiO4), bridgmanite ([Mg,Fe]SiO3), serpentine ([Mg,Fe,]2-3Si2O5[OH)]4), and pyrrhotite (Fe(1-x)S), are an essential requirement in planetary bodies to produce such disequilibria and, thereby, life. Yet only two minerals, fougerite ([Fe2+6xFe3+6(x-1)O12H2(7-3x)]2+·[(CO2-)·3H2O]2-) and mackinawite (Fe[Ni]S), are vital-comprising precipitate membranes-as initial "free energy" conductors and converters of such disequilibria, i.e., as the initiators of a CO2-reducing metabolism. The fact that wet and rocky bodies in the solar system much smaller than Earth or Venus do not reach the internal pressure (≥23 GPa) requirements in their mantles sufficient for producing bridgmanite and, therefore, are too reduced to stabilize and emit CO2-the staple of life-may explain the apparent absence or negligible concentrations of that gas on these bodies, and thereby serves as a constraint in the search for extraterrestrial life. The astrobiological challenge then is to search for worlds that (i) are large enough to generate internal pressures such as to produce bridgmanite or (ii) boast electron acceptors, including imported CO2, from extraterrestrial sources in their hydrospheres.

Redox state of Earth's magma ocean and its Venus-like early atmosphere

Exchange between a magma ocean and vapor produced Earth's earliest atmosphere. Its speciation depends on the oxygen fugacity (fO₂) set by the Fe³⁺/Fe²⁺ ratio of the magma ocean at its surface. Here, we establish the relationship between fO₂ and Fe³⁺/Fe²⁺ in quenched liquids of silicate Earth-like composition at 2173 K and 1 bar. Mantle-derived rocks have Fe³⁺/(Fe³⁺+Fe²⁺) = 0.037 ± 0.005, at which the magma ocean defines an fO₂ 0.5 log units above the iron-wüstite buffer. At this fO₂, the solubilities of H-C-N-O species in the magma ocean produce a CO-rich atmosphere. Cooling and condensation of H₂O would have led to a prebiotic terrestrial atmosphere composed of CO₂-N₂, in proportions and at pressures akin to those observed on Venus. Present-day differences between Earth's atmosphere and those of her planetary neighbors result from Earth's heliocentric location and mass, which allowed geologically long-lived oceans, in-turn facilitating CO₂ drawdown and, eventually, the development of life.

Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

CRAHCN-O: A Consistent Reduced Atmospheric Hybrid Chemical Network Oxygen Extension for Hydrogen Cyanide and Formaldehyde Chemistry in CO2-, N2-, H2O-, CH4-, and H2-Dominated Atmospheres

Hydrogen cyanide (HCN) and formaldehyde (H₂CO) are key precursors to biomolecules such as nucleobases and amino acids in planetary atmospheres. However, many reactions which produce and destroy these species in atmospheres containing CO₂ and H₂O are still missing from the literature. We use a quantum chemistry approach to find these missing reactions and calculate their rate coefficients using canonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus/master equation theory at the BHandHLYP/aug-cc-pVDZ level of theory. We calculate the rate coefficients for 126 total reactions and validate our calculations by comparing with experimental data in the 39% of available cases. Our calculated rate coefficients are most frequently within a factor of 2 of experimental values and generally always within an order of magnitude of these values. We discover 45 previously unknown reactions and identify 6 from this list that are most likely to dominate H₂CO and HCN production and destruction in planetary atmospheres. We highlight ¹O + CH₃ → H₂CO + H as a new key source and H₂CO + ¹O → HCO + OH as a new key sink, for H₂CO in upper planetary atmospheres. In this effort, we develop an oxygen extension to our consistent reduced atmospheric hybrid chemical network (CRAHCN-O), building off our previously developed network for HCN production in N₂-, CH₄-, and H₂-dominated atmospheres (CRAHCN). This extension can be used to simulate both HCN and H₂CO production in atmospheres dominated by any of CO₂, N₂, H₂O, CH₄, and H₂.

Cometary Delivery of Hydrogen Cyanide to the Early Earth

Delivery of water and organics by asteroid and comet impacts may have influenced prebiotic chemistry on the early Earth. Some recent prebiotic chemistry experiments emphasize hydrogen cyanide (HCN) as a feedstock molecule for the formation of sugars, ribonucleotides, amino acids, and lipid precursors. Here, we assess how much HCN originally contained in a comet would survive impact, using parametric temperature and pressure profiles together with a time-dependent chemistry model. We find that HCN survival mainly depends on whether the impact is hot enough to thermally decompose H₂O into reactive radicals, and HCN is therefore rather insensitive to the details of the chemistry. In the most favorable impacts (low impact angle, low velocity, small radius), this temperature threshold is not reached, and intact delivery of HCN is possible. We estimate the global delivery of HCN during a period of Early and Late Heavy Bombardment of the early Earth, as well as local HCN concentrations achieved by individual impacts. In the latter case, comet impacts can provide prebiotically interesting HCN levels for thousands to millions of years, depending on properties of the impactor and of the local environment.

Mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets

Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. The oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. Here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. We further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 Earth masses. We show that outgassing of reduced systems is dominated by strongly reduced gases such as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {H}_{2}$$\end{document}H2, with only smaller fractions of moderately reduced/oxidised gases (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {CO}$$\end{document}CO, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {H}_{2}\text {O}$$\end{document}H2O). Overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. Atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states.

Impact-induced amino acid formation on Hadean Earth and Noachian Mars

Abiotic synthesis of biomolecules is an essential step for the chemical origin of life. Many attempts have succeeded in synthesizing biomolecules, including amino acids and nucleobases (e.g., via spark discharge, impact shock, and hydrothermal heating), from reduced compounds that may have been limited in their availabilities on Hadean Earth and Noachian Mars. On the other hand, formation of amino-acids and nucleobases from CO2 and N2 (i.e., the most abundant C and N sources on Earth during the Hadean) has been limited via spark discharge. Here, we demonstrate the synthesis of amino acids by laboratory impact-induced reactions among simple inorganic mixtures: Fe, Ni, Mg2SiO4, H2O, CO2, and N2, by coupling the reduction of CO2, N2, and H2O with the oxidation of metallic Fe and Ni. These chemical processes simulated the possible reactions at impacts of Fe-bearing meteorites/asteroids on oceans with a CO2 and N2 atmosphere. The results indicate that hypervelocity impact was a source of amino acids on the Earth during the Hadean and potentially on Mars during the Noachian. Amino acids formed during such events could more readily polymerize in the next step of the chemical evolution, as impact events locally form amino acids at the impact sites.

Mantle data imply a decline of oxidizable volcanic gases could have triggered the Great Oxidation

Aerobic lifeforms, including humans, thrive because of abundant atmospheric O₂, but for much of Earth history O₂ levels were low. Even after evidence for oxygenic photosynthesis appeared, the atmosphere remained anoxic for hundreds of millions of years until the ~2.4 Ga Great Oxidation Event. The delay of atmospheric oxygenation and its timing remain poorly understood. Two recent studies reveal that the mantle gradually oxidized from the Archean onwards, leading to speculation that such oxidation enabled atmospheric oxygenation. But whether this mechanism works has not been quantitatively examined. Here, we show that these data imply that reducing Archean volcanic gases could have prevented atmospheric O₂ from accumulating until ~2.5 Ga with ≥95% probability. For two decades, mantle oxidation has been dismissed as a key driver of the evolution of O₂ and aerobic life. Our findings warrant a reconsideration for Earth and Earth-like exoplanets.

The early Earth’s atmosphere had very low oxygen levels for hundreds of millions of years, until the 2.4 Ga Great Oxidation Event, which remains poorly understood. Here, the authors show that reducing Archean volcanic gases could have prevented atmospheric O₂ from accumulating, and therefore mantle oxidation was likely very important in setting the evolution of O₂ and aerobic life.

A magma ocean origin to divergent redox evolutions of rocky planetary bodies and early atmospheres

Magma oceans were once ubiquitous in the early solar system, setting up the initial conditions for different evolutionary paths of planetary bodies. In particular, the redox conditions of magma oceans may have profound influence on the redox state of subsequently formed mantles and the overlying atmospheres. The relevant redox buffering reactions, however, remain poorly constrained. Using first-principles simulations combined with thermodynamic modeling, we show that magma oceans of Earth, Mars, and the Moon are likely characterized with a vertical gradient in oxygen fugacity with deeper magma oceans invoking more oxidizing surface conditions. This redox zonation may be the major cause for the Earth's upper mantle being more oxidized than Mars' and the Moon's. These contrasting redox profiles also suggest that Earth's early atmosphere was dominated by CO2 and H2O, in contrast to those enriched in H2O and H2 for Mars, and H2 and CO for the Moon.

An andesitic source for Jack Hills zircon supports onset of plate tectonics in the Hadean

The composition and origin of Earth’s early crust remains hotly debated. Here we use partition coefficients to invert the trace element composition of 4.3–3.3 Gyr Jack Hills zircons to calculate the composition of the melts from which they crystallised. Using this approach, the average SiO₂ content of these melts was 59 ± 6 wt. % with Th/Nb, Dy/Yb and Sr/Y ratios of 2.7 ± 1.9, 0.9 ± 0.2 and 1.6 ± 0.7, respectively. Such features strongly indicate that the protolith for the Jack Hills zircons was not an intra-plate mafic rock, nor a TTG (tondjhemite-tonalite-granodiorite) or a Sudbury-like impact melt. Instead, the inferred equilibrium melts are much more similar to andesites formed in modern subduction settings. We find no evidence for any secular variation between 4.3 and 3.3 Gyr implying little change in the composition or tectonic affinity of the Earth’s early crust from the Hadean to Mesoarchaean.

The composition and tectonic affiliation of Earth's earliest crust remains disputed. Here, the authors find that Archean Jack Hills zircons crystallized from melts with compositions similar to andesite formed in modern subduction settings, which they suggest is consistent with an early onset of modern-style plate tectonics on Earth.

Deep magma ocean formation set the oxidation state of Earth's mantle

The composition of Earth's atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth's core started to form. Through high-pressure experiments, we found that Fe²⁺ in a deep magma ocean would disproportionate to Fe³⁺ plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO₂ from the atmosphere to precipitate as diamond at depth. This explains Earth's carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.

Mineral self-organization on a lifeless planet

It has been experimentally demonstrated that, under alkaline conditions, silica is able to induce the formation of mineral self-assembled inorganic-inorganic composite materials similar in morphology, texture and nanostructure to the hybrid biomineral structures that, millions of years later, life was able to self-organize. These mineral self-organized structures (MISOS) have been also shown to work as effective catalysts for prebiotic chemical reactions and to easily create compartmentalization within the solutions where they form. We reason that, during the very earliest history of this planet, there was a geochemical scenario that inevitably led to the existence of a large-scale factory of simple and complex organic compounds, many of which were relevant to prebiotic chemistry. The factory was built on a silica-rich high-pH ocean and powered by two main factors: a) a quasi-infinite source of simple carbon molecules synthesized abiotically from reactions associated with serpentinization, or transported from meteorites and produced from their impact on that alkaline ocean, and b) the formation of self-organized silica-metal mineral composites that catalyze the condensation of simple molecules in a methane-rich reduced atmosphere. We discuss the plausibility of this geochemical scenario, review the details of the formation of MISOS and its catalytic properties and the transition towards a slightly alkaline to neutral ocean.

Introduction to virus origins and their role in biological evolution

Viruses are diverse parasites of cells and extremely abundant. They might have arisen during an early phase of the evolution of life on Earth dominated by ribonucleic acid or RNA-like macromolecules, or when a cellular world was already well established. The theories of the origin of life on Earth shed light on the possible origin of primitive viruses or virus-like genetic elements in our biosphere. Some features of present-day viruses, notably error-prone replication, might be a consequence of the selective forces that mediated their ancestral origin. Two views on the role of viruses in our biosphere predominate; viruses considered as opportunistic, selfish elements, and viruses considered as active participants in the construction of the cellular world via the lateral transfer of genes. These two models have a bearing on viruses being considered predominantly as disease agents or predominantly as cooperators in the shaping of differentiated cellular organisms.

Hydrogen isotopic evidence for early oxidation of silicate Earth

The Moon-forming giant impact extensively melts and partially vaporizes the silicate Earth and delivers a substantial mass of metal to Earth's core. The subsequent evolution of the magma ocean and overlying atmosphere has been described by theoretical models but observable constraints on this epoch have proved elusive. Here, we report thermodynamic and climate calculations of the primordial atmosphere during the magma ocean and water ocean epochs respectively and forge new links with observations to gain insight into the behavior of volatiles on the Hadean Earth. As accretion wanes, Earth's magma ocean crystallizes, outgassing the bulk of its volatiles into the primordial atmosphere. The redox state of the magma ocean controls both the chemical composition of the outgassed volatiles and the hydrogen isotopic composition of water oceans that remain after hydrogen escape from the primordial atmosphere. The climate modeling indicates that multi-bar H₂-rich atmospheres generate sufficient greenhouse warming and rapid kinetics resulting in ocean-atmosphere H₂O-H₂ isotopic equilibration. Whereas water condenses and is mostly retained, molecular hydrogen does not condense and can escape, allowing large quantities (~10² bars) of hydrogen - if present - to be lost from the Earth in this epoch. Because the escaping inventory of H can be comparable to the hydrogen inventory in primordial water oceans, equilibrium deuterium enrichment can be large with a magnitude that depends on the initial atmospheric H₂ inventory. Under equilibrium partitioning, the water molecule concentrates deuterium and, to the extent that hydrogen in other forms (e.g., H₂) are significant species in the outgassed atmosphere, pronounced D/H enrichments (~1.5-2x) in the oceans are expected from equilibrium partitioning in this epoch. By contrast, the common view that terrestrial water has a carbonaceous chondritic source requires the oceans to preserve the isotopic composition of that source, undergoing minimal D-enrichment via equilibration with H₂ followed by hydrodynamic escape. Such minimal enrichment places upper limits on the amount of primordial atmospheric H₂ in contact with Hadean water oceans and implies oxidizing conditions (logfO₂>IW+1, H₂/H₂O<0.3) for outgassing from the magma ocean. Preservation of an approximate carbonaceous chondrite D/H signature in the oceans thus provides evidence that the observed oxidation of silicate Earth occurred before crystallization of the final magma ocean, yielding a new constraint on the timing of this critical event in Earth history. The seawater-carbonaceous chondrite "match" in D/H (to ~10-20%) further constrains the prior existence of an atmospheric H₂ inventory - of any origin - on post-giant-impact Earth to <20 bars, and suggests that the terrestrial mantle supplied the oxidant for the chemical resorption of metals during terrestrial late accretion.

Prebiotic Chemistry that Could Not Not Have Happened

We present a direct route by which RNA might have emerged in the Hadean from a fayalite–magnetite mantle, volcanic SO₂ gas, and well-accepted processes that must have created substantial amounts of HCHO and catalytic amounts of glycolaldehyde in the Hadean atmosphere. In chemistry that could not not have happened, these would have generated stable bisulfite addition products that must have rained to the surface, where they unavoidably would have slowly released reactive species that generated higher carbohydrates. The formation of higher carbohydrates is self-limited by bisulfite formation, while borate minerals may have controlled aldol reactions that occurred on any semi-arid surface to capture that precipitation. All of these processes have well-studied laboratory correlates. Further, any semi-arid land with phosphate should have had phosphate anhydrides that, with NH₃, gave carbohydrate derivatives that directly react with nucleobases to form the canonical nucleosides. These are phosphorylated by magnesium borophosphate minerals (e.g., lüneburgite) and/or trimetaphosphate-borate with Ni²⁺ catalysis to give nucleoside 5′-diphosphates, which oligomerize to RNA via a variety of mechanisms. The reduced precursors that are required to form the nucleobases came, in this path-hypothesis, from one or more mid-sized (10²³–10²⁰ kg) impactors that almost certainly arrived after the Moon-forming event. Their iron metal content almost certainly generated ammonia, nucleobase precursors, and other reduced species in the Hadean atmosphere after it transiently placed the atmosphere out of redox equilibrium with the mantle. In addition to the inevitability of steps in this path-hypothesis on a Hadean Earth if it had semi-arid land, these processes may also have occurred on Mars. Adapted from a lecture by the Corresponding Author at the All-Russia Science Festival at the Lomonosov Moscow State University on 12 October 2019, and is an outcome of a three year project supported by the John Templeton Foundation and the NASA Astrobiology program. Dedicated to David Deamer, on the occasion of his 80th Birthday.

A Stark Contrast to Modern Earth: Phosphate Mineral Transformation and Nucleoside Phosphorylation in an Iron- and Cyanide-Rich Early Earth Scenario

Organophosphates were likely an important class of prebiotic molecules. However, their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals, is widely viewed as a major barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea-based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a "warm little pond" scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes, urea, ammonium formate, and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allow us to propose a holistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals, allowing significant organic phosphorylation under plausible prebiotic conditions.

Geochronology, Oxidization State and Source of the Daocheng Batholith, Yidun Arc: Implications for Regional Metallogenesis

The Daocheng batholith consists of granite, granodiorite and K-feldspar megacrystic granite, which is located in the north Yidun Arc. It is a barren batholith in contrast to plutons of the same age that contain major copper deposits, such as Pulang to the south. In the Daocheng, abundant mafic microgranular enclaves (MMEs) mainly developed within granodiorite and K-feldspar megacrystic granite, which are characterized by quenched apatite, quartz eyes and plagioclase phenocrysts. LA-ICP-MS zircon U–Pb dating of host granodiorite yielded ages ranging from 223 Ma to 210 Ma, with a weighted mean of 215.3 ± 1.8 Ma. Zircons from MMEs yielded ages ranging from 218 Ma to 209 Ma, with a weighted mean of 214.2 ± 1.4 Ma. Geochemical analyses show that granodiorite is high-K, calc-alkaline and I-type, with SiO2 contents ranging from 67.90% to 70.54%. These rocks are metaluminous to marginally peraluminous (A/CNK = 0.98–1.00) and moderately rich in alkalis with K2O ranging from 3.28% to 4.59% and Na2O ranging from 3.18% to 3.20%, with low MgO (1.08%–1.29%), Cr (12.7 ppm–16.8 ppm), Ni (5.19 ppm–6.16 ppm) and Mg# (35–49). The MMEs have relatively low SiO2 contents (56.34%–60.91%), higher Al2O3 contents (16.06%–17.98%), higher MgO and FeO abundances and are metaluminous (A/CNK = 0.82–0.83). The MMEs and host granodiorite are enriched in light rare-earth elements (LREEs) relative to heavy rare-earth elements (HREEs), with slightly negative Eu anomalies, and enriched in Th, U and large ion lithophile elements (LILEs; e.g., K, Rb and Pb), and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, P and Ti), showing affinities typical of arc magmas. The zircon εHf(t) values (−6.28 to −2.33) and ancient two-stage Hf model ages of 1.92 to 1.25 Ga, indicating that the magmas are generally melts that incorporated significant portions of Precambrian crust. The relatively low silica contents and high Mg# values of the MMEs, and the linear patterns of MgO, Al2O3 and Fe2O3 with SiO2 between the MMEs and host granodiorite, showing the formation of MMEs are genetically related to magma mixing. The Daocheng granodiorite is characterized by much lower zircon Ce4+/Ce3+ (average of 3.53) and low fO2 value (average of ∆FMQ = –10.84), whereas the ore-bearing quartz monzonite porphyries in the Pulang copper deposit are characterized by much higher zircon Ce4+/Ce3+ (average of 52.10) and high fO2 value (average of ∆FMQ = 2.8), indicating the ore-bearing porphyry intrusions had much higher fO2 of magma than the ore-barren intrusions considering that the high oxygen fugacity of the magma is conducive to mineralization.

Redox rebalance against genetic perturbations and modulation of central carbon metabolism by the oxidative stress regulation

The micro-aerophilic organisms and aerobes as well as yeast and higher organisms have evolved to gain energy through respiration (via oxidative phosphorylation), thereby enabling them to grow much faster than anaerobes. However, during respiration, reactive oxygen species (ROSs) are inherently (inevitably) generated, and threaten the cell's survival. Therefore, living organisms (or cells) must furnish the potent defense systems to keep such ROSs at harmless level, where the cofactor balance plays crucial roles. Namely, NADH is the source of energy generation (catabolism) in the respiratory chain reactions, through which ROSs are generated, while NADPH plays important roles not only for the cell synthesis (anabolism) but also for detoxifying ROSs. Therefore, the cell must rebalance the redox ratio by modulating the fluxes of the central carbon metabolism (CCM) by regulating the multi-level regulation machinery upon genetic perturbations and the change in the growth conditions. Here, we discuss about how aerobes accomplish such cofactor homeostasis against redox perturbations. In particular, we consider how single-gene mutants (including pgi, pfk, zwf, gnd and pyk mutants) modulate their metabolisms in relation to cofactor rebalance (and also by adaptive laboratory evolution). We also discuss about how the overproduction of NADPH (by the pathway gene mutation) can be utilized for the efficient production of useful value-added chemicals such as medicinal compounds, polyhydroxyalkanoates, and amino acids, all of which require NADPH in their synthetic pathways. We then discuss about the metabolic responses against oxidative stress, where αketoacids play important roles not only for the coordination between catabolism and anabolism, but also for detoxifying ROSs by non-enzymatic reactions, as well as for reducing the production of ROSs by repressing the activities of the TCA cycle and respiration (via carbon catabolite repression). Thus, we discuss about the mechanisms (basic strategies) that modulate the metabolism from respiration to respiro-fermentative metabolism causing overflow, based on the role of Pyk activity, affecting the NADPH production at the oxidative pentose phosphate (PP) pathway, and the roles of αketoacids for the change in the source of energy generation from the oxidative phosphorylation to the substrate level phosphorylation.

Formation of the Granodiorite-Hosting Magushan Cu–Mo Polymetallic Deposit in Southern Anhui, Eastern China: Evidences from Geochronology and Geochemistry

The newly discovered Magushan Cu-Mo polymetallic deposit, located in southeastern Anhui, eastern China, is a middle-scale skarn-type polymetallic deposit with different ore types of veinlets-disseminated skarn (the primary type), quartz veins, and porphyry. LA-ICP-MS zircon U–Pb analyses yielded a crystallization age of 135.7 ± 1.5 Ma for the ore-related granodiorite in Magushan. The granodiorites are I-type granites in nature, characterized by metaluminous and high-K calc-alkaline characteristics. They are enriched in large ion lithophile elements (LILEs, e.g., Ba, Th, and U) and light rare earth elements (LREEs), and depleted in high field strength elements (NFSEs, e.g., Nb, Ta, and Ti) and heavy rare earth element (HREEs), with slightly negative Eu anomalies (Eu/Eu* = 0.81–0.86). These granodiorites show high Mg# (mainly > 40) values, high MgO (1.73–1.96 wt. %) and low Na2O (<4.21 wt. %) contents, with whole-rock (87Sr/86Sr)i ratios (0.708877 to 0.710398), negative εNd(t) values of −5.4 to −5.2, and negative zircon εHf(t) values of −4.60 to −1.37, with old two-stage Hf model ages (TDM2) between 1.2‒1.5 Ga. Besides, they are characterized by high radiogenic Pb isotopic compositions with (206Pb/204Pb)i = 18.44–18.56, (207Pb/204Pb)i = 15.66–15.67, and (208Pb/204Pb)i = 38.77–38.87. These granodiorites are characterized by high zircon Ce4+/Ce3+ ratios (average 893) and Eu/Eu* ratios (average 0.51), indicating high magmatic oxygen fugacities. The distinct geochemical and isotopic features suggest that the Magushan granodiorites could be formed by metasomatized mantle-derived magmas, mixing with materials from Neoproterozoic crust that is widely distributed in the Southern Anhui. This study concludes that the formation of the Magushan Cu-Mo polymetallic deposits may largely depend on an oxidizing environment and multi-sources mixed of mantle- and crust-derived materials.

The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats

Since the Archean, N₂ has been a major atmospheric constituent in Earth's atmosphere. Nitrogen is an essential element in the building blocks of life; therefore, the geobiological nitrogen cycle is a fundamental factor in the long-term evolution of both Earth and Earth-like exoplanets. We discuss the development of Earth's N₂ atmosphere since the planet's formation and its relation with the geobiological cycle. Then we suggest atmospheric evolution scenarios and their possible interaction with life-forms: first for a stagnant-lid anoxic world, second for a tectonically active anoxic world, and third for an oxidized tectonically active world. Furthermore, we discuss a possible demise of present Earth's biosphere and its effects on the atmosphere. Since life-forms are the most efficient means for recycling deposited nitrogen back into the atmosphere at present, they sustain its surface partial pressure at high levels. Also, the simultaneous presence of significant N₂ and O₂ is chemically incompatible in an atmosphere over geological timescales. Thus, we argue that an N₂-dominated atmosphere in combination with O₂ on Earth-like planets within circumstellar habitable zones can be considered as a geo-biosignature. Terrestrial planets with such atmospheres will have an operating tectonic regime connected with an aerobic biosphere, whereas other scenarios in most cases end up with a CO₂-dominated atmosphere. We conclude with implications for the search for life on Earth-like exoplanets inside the habitable zones of M to K stars.

Organometallic compounds as carriers of extraterrestrial cyanide in primitive meteorites

Extraterrestrial delivery of cyanide may have been crucial for the origin of life on Earth since cyanide is involved in the abiotic synthesis of numerous organic compounds found in extant life; however, little is known about the abundance and species of cyanide present in meteorites. Here, we report cyanide abundance in a set of CM chondrites ranging from 50 ± 1 to 2472 ± 38 nmol·g-1, which relates to the degree of aqueous alteration of the meteorite and indicates that parent body processing influenced cyanide abundance. Analysis of the Lewis Cliff 85311 meteorite shows that its releasable cyanide is primarily in the form of [FeII(CN)5(CO)]3- and [FeII(CN)4(CO)2]2-. Meteoritic delivery of iron cyanocarbonyl complexes to early Earth likely provided an important point source of free cyanide. Iron cyanocarbonyl complexes may have served as precursors to the unusual FeII(CN)(CO) moieties that form the catalytic centers of hydrogenases, which are thought to be among the earliest enzymes.