Search Results (32)

The ubiquitous, evolutionarily oldest RNAs and proteins exclusively use rather rare zinc as transition metal cofactor and potassium as alkali metal cofactor, which implies their abundance in the habitats of the first organisms. Intriguingly, lunar rocks contain a hundred times less zinc and ten times less potassium than the Earth’s crust; the Moon is also depleted in other moderately volatile elements (MVEs). Current theories of impact formation of the Moon attribute this depletion to the MVEs still being in a gaseous state when the hot post-impact disk contracted and separated from the nascent Moon. The MVEs then fell out onto juvenile Earth’s protocrust; zinc, as the most volatile metal, precipitated last, just after potassium. According to our calculations, the top layer of the protocrust must have contained up to 10¹⁹ kg of metallic zinc, a powerful reductant. The venting of hot geothermal fluids through this MVE-fallout layer, rich in metallic zinc and radioactive potassium, both capable of reducing carbon dioxide and dinitrogen, must have yielded a plethora of organic molecules released with the geothermal vapor. In the pools of vapor condensate, the RNA-like molecules may have emerged through a pre-Darwinian selection for low-volatile, associative, mineral-affine, radiation-resistant, nitrogen-rich, and polymerizable molecules. Full article

Cyanide is a crucial reagent for the synthesis of biomolecules in prebiotic chemistry. However, effective organic synthesis requires cyanide to be concentrated. One proposed mechanism for cyanide storage and concentration on Early Earth involves the formation of aqueous ferrocyanide complexes. In basic pH conditions, cyanide will spontaneously form ferrocyanide complexes in the presence of aqueous Fe(II). While ferrocyanide aqueous complex formation is well defined, the potential for Fe(II)-bearing minerals to react with cyanide to form ferrocyanide complexes or store cyanide on the mineral surface has yet to be explored under prebiotically relevant conditions. In this study, we demonstrate that when cyanide interacts with ferroan brucite (Mg_xFe_1−x(OH)₂), cyanide will both form aqueous and mineral-surface-adsorbed ferrocyanide implying that there are two reservoirs that cyanide will partition into. In addition, we found that cyanide decreased the amount of hydrogen gas produced by the oxidation of ferroan brucite, indicating that cyanide alters the mineral’s redox reactivity. The cyanide adsorbed on brucite can be released by a decrease in pH, which leads to the dissolution of ferroan brucite, thus releasing the adsorbed cyanide. Our findings suggest that iron-bearing minerals may represent an overlooked storage reservoir of cyanide on Hadean Earth, potentially playing a significant role in cyanide availability for prebiotic chemistry. Full article

Amino acids are one of the most important building blocks of life. During the biochemical process of translation, cells sequentially connect amino acids via amide bonds to synthesize proteins, using the genetic information in messenger RNA (mRNA) as a template. From a prebiotic perspective (i.e., without enzymatic catalysis), joining amino acids to peptides via amide bonds is difficult due to the highly endergonic nature of the condensation reaction. We show here that amides can be formed in reactions catalyzed by the transition metal sulfides from acetylene, carbon monoxide and ammonia under aqueous conditions. Some α- and β-amino acids were also formed under the same conditions, demonstrating an alternative cyanide-free path for the formation of amino acids in prebiotic environments. Experiments performed with stable isotope labeled precursors, like ¹⁵NH₄Cl and ¹³C-acetylene, enabled the accurate mass spectroscopic identification of the products formed from the starting materials and their composition. Reactions catalyzed using the transition metal sulfides seem to offer a promising alternative pathway for the formation of amides and amino acids in prebiotic environments, bypassing the challenges posed by the highly endergonic condensation reaction. These findings shed light on the potential mechanisms by which the building blocks of life could have originated on early Earth. Full article

Fixed nitrogen species generated by the early Earth’s atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth’s N₂/CO₂-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NO_x species (i.e., no HCN formation) via the thermochemical dissociation of N₂ and CO₂ in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth’s early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN₂, inspired by the experimental results which suggest that reactions with CH radicals (from CH₄ photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN₂ reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe. Full article

Darwin’s theory of evolution by natural selection was revolutionary because it provided a mechanism by which variation could be selected. This mechanism can only operate on living systems and thus cannot be applied to the origin of life. Here, we propose a viable alternative mechanism for prebiotic systems: autocatalytic selection, in which molecules catalyze reactions and processes that lead to increases in their concentration. Crucially, this provides a driver for increases in concentrations of molecules to a level that permits prebiotic metabolism. We show how this can produce high levels of amino acids, sugar phosphates, nucleotides and lipids and then lead on to polymers. Our outline is supported by a set of guidelines to support the identification of the most likely prebiotic routes. Most of the steps in this pathway are already supported by experimental results. These proposals generate a coherent and viable set of pathways that run from established Hadean geochemistry to the beginning of life. Full article

Giant impacts can generate transient hydrogen-rich atmospheres, reducing atmospheric carbon. The reduced carbon will form hazes that rain out onto the surface and can become incorporated into the crust. Once heated, a large fraction of the carbon is converted into graphite. The result is that local regions of the Hadean crust were plausibly saturated with graphite. We explore the consequences of such a crust for a prebiotic surface hydrothermal vent scenario. We model a surface vent fed by nitrogen-rich volcanic gas from high-temperature magmas passing through graphite-saturated crust. We consider this occurring at pressures of 1–$1000\mathrm{bar}$ and temperatures of 1500–$1700{}^{\circ }\mathrm{C}$. The equilibrium with graphite purifies the leftover gas, resulting in substantial quantities of nitriles ($0.1\%$ HCN and $1\mathrm{ppm}$ HC₃N) and isonitriles ($0.01\%$ HNC) relevant for prebiotic chemistry. We use these results to predict gas-phase concentrations of methyl isocyanide of ∼1 ppm. Methyl isocyanide can participate in the non-enzymatic activation and ligation of the monomeric building blocks of life, and surface or shallow hydrothermal environments provide its only known equilibrium geochemical source. Full article

The origin of life on earth requires the synthesis of protobiopolymers in realistic geologic environments along strictly abiotic pathways that rely on inorganic phases (such as minerals) instead of cellular machinery to promote condensation. One such class of polymer central to biochemistry is the polynucleotides, and oligomerization of activated ribonucleotides has been widely studied. Nonetheless, the range of laboratory conditions tested to date is limited and the impact of realistic early Earth conditions on condensation reactions remains unexplored. Here, we investigate the potential for a variety of minerals to enhance oligomerization using ribonucleotide monomers as one example to model condensation under plausible planetary conditions. The results show that several minerals differing in both structure and composition enhance oligomerization. Sulfide minerals yielded oligomers of comparable lengths to those formed in the presence of clays, with galena being the most effective, yielding oligonucleotides up to six bases long. Montmorillonite continues to excel beyond other clays. Chemical pretreatment of the clay was not required, though maximum oligomer lengths decreased from ~11 to 6 bases. These results demonstrate the diversity of mineral phases that can impact condensation reactions and highlight the need for greater consideration of environmental context when assessing prebiotic synthesis and the origin of life. Full article

Understanding the composition, formation and evolution of the oldest continental crust is crucial for comprehending the mechanism and timing of crustal growth and differentiation on early Earth. However, the preservation of the ancient continental crust is limited due to extensive reworking by later tectonothermal events. In the Lulong area of eastern Hebei, abundant ca. 3.8–3.4 Ga detrital zircons of the fuchsite quartzite have been previously identified. Nonetheless, the provenance and Hf isotopic compositions of the fuchsite quartzite remain unclear. In this study, we present new detrital zircon ages and Hf isotopic for the fuchsite quartzite in the Lulong area to establish the timing of deposition, the provenance and the regional stratigraphic relationship. Zircon U-Pb dating indicates that the fuchsite quartzite was deposited between 3.3–3.1 Ga and most grains were sourced from the 3.8 Ga TTG gneisses and Paleoarchean magmas. Field investigations and regional correlations reveal that the fuchsite quartzite from the Lulong area is equivalent to that of the Caozhuang area. Zircon Hf isotopic data from eastern Hebei Province (Lulong and Caozhuang areas) and Anshan and Xinyang areas indicate that the oldest crustal growth event of North China Craton occurred in the Hadean. Full article

A survey of the average Mohs hardness of minerals throughout Earth’s history reveals a significant and systematic decrease from >6 in presolar grains to ~5 for Archean lithologies to <4 for Phanerozoic minerals. Two primary factors contribute to this temporal decrease in the average Mohs hardness. First, selective losses of softer minerals throughout billions of years of near-surface processing lead to preservational biases in the mineral record. Second, changes in the processes of mineral formation play a significant role because more ancient refractory stellar phases and primary igneous minerals of the Hadean/Archean Eon are intrinsically harder than more recently weathered products, especially following the Paleoproterozoic Great Oxidation Event and the production of Phanerozoic biominerals. Additionally, anthropogenic sampling biases resulting from the selective exploration and curation of the mineralogical record may be superimposed on these two factors. Full article

Life most likely started during the Hadean Eon; however, the environmental conditions which contributed to the complexity of its chemistry are poorly known. A better understanding of various environmental conditions, including global (heliospheric) and local (atmospheric, surface, and oceanic), along with the internal dynamic conditions of the early Earth, are required to understand the onset of abiogenesis. Herein, we examine the contributions of galactic cosmic rays (GCRs) and solar energetic particles (SEPs) associated with superflares from the young Sun to the formation of amino acids and carboxylic acids in weakly reduced gas mixtures representing the early Earth’s atmosphere. We also compare the products with those introduced by lightning events and solar ultraviolet light (UV). In a series of laboratory experiments, we detected and characterized the formation of amino acids and carboxylic acids via proton irradiation of a mixture of carbon dioxide, methane, nitrogen, and water in various mixing ratios. These experiments show the detection of amino acids after acid hydrolysis when 0.5% (v/v) of initial methane was introduced to the gas mixture. In the set of experiments with spark discharges (simulation of lightning flashes) performed for the same gas mixture, we found that at least 15% methane was required to detect the formation of amino acids, and no amino acids were detected in experiments via UV irradiation, even when 50% methane was used. Carboxylic acids were formed in non-reducing gas mixtures (0% methane) by proton irradiation and spark discharges. Hence, we suggest that GCRs and SEP events from the young Sun represent the most effective energy sources for the prebiotic formation of biologically important organic compounds from weakly reducing atmospheres. Since the energy flux of space weather, which generated frequent SEPs from the young Sun in the first 600 million years after the birth of the solar system, was expected to be much greater than that of GCRs, we conclude that SEP-driven energetic protons are the most promising energy sources for the prebiotic production of bioorganic compounds in the atmosphere of the Hadean Earth. Full article

The in-fall of meteorites and interstellar dust particles during the Hadean–Archean heavy bombardment may have provided the early Earth with various reduced oxidation state phosphorus compounds and minerals, including phosphite (HPO₃²⁻)([Pi(III)]). The ion phosphite ([Pi(III)])has been postulated to be ubiquitous on the early Earth and consequently could have played a role in the emergence of organophosphorus compounds and other prebiotically relevant P species such as condensed P compounds, e.g., pyrophosphite ([PPi(III)]) and isohypophosphate ([PPi(III–V)]). In the present study, we show that phosphite ([Pi(III)]) oxidizes under mild heating conditions (e.g., wet–dry cycles and a prebiotic scenario mimicking a mildly hot-evaporating/drying pool on the early Earth at 78–83 °C) in the presence of urea and other additives, resulting in changes to orthophosphate ([Pi(V)]) alongside the formation of reactive condensed P compounds (e.g., pyrophosphite ([PPi(III)]) and isohypophosphate ([PPi(III–V)])) through a one-pot mechanism. Additionally, we also show that phosphite ([Pi(III)]) and the condensed P compounds readily react with organics (nucleosides and organic alcohol) to form organophosphorus compounds. Full article

The emergence of life has been a subject of intensive research for decades. Different approaches and different environmental “cradles” have been studied, from space to the deep sea. Since the recent discovery of a natural electrical current through deep-sea hydrothermal vents, a new energy source is considered for the transition from inorganic to organic. This energy source (electron donor) is used by modern microorganisms via a new trophic type, called electrotrophy. In this review, we draw a parallel between this metabolism and a new theory for the emergence of life based on this electrical electron flow. Each step of the creation of life is revised in the new light of this prebiotic electrochemical context, going from the evaluation of similar electrical current during the Hadean, the CO₂ electroreduction into a prebiotic primordial soup, the production of proto-membranes, the energetic system inspired of the nitrate reduction, the proton gradient, and the transition to a planktonic proto-cell. Finally, this theory is compared to the two other theories in hydrothermal context to assess its relevance and overcome the limitations of each. Many critical factors that were limiting each theory can be overcome given the effect of electrochemical reactions and the environmental changes produced. Full article

The role of minerals in the chemical evolution of RNA molecules is an important issue when considering the early stage of the Hadean Earth. In particular, the interaction between functional ribozymes and ancient minerals under simulated primitive conditions is a recent research focus. We are currently attempting to design a primitive RNA metabolic network which would function with minerals, and believe that the simulated chemical network of RNA molecules would be useful for evaluation of the chemical evolution from a simple RNA mixture to an RNA-based life-like system. First, we measured the binding interactions of oligonucleotides with four types of minerals; Aerosil silica, zirconium silicate, sepiolite, and montmorillonite. Oligonucleotides bound zirconium silicate and montmorillonite in the presence of MgCl₂, and bound sepiolite both in the presence and absence of MgCl₂, but they did not bind Aerosil. Based on the binding behavior, we attempted the self-cleavage reaction of the hammerhead ribozyme from an avocado viroid. This reaction was strongly inhibited by zirconium silicate, a compound regarded as mineral evidence for the existence of water. The present study suggests that the chemical evolution of functional RNA molecules requires specific conformational binding, resulting in efficient ribozyme function as well as zirconium silicate for the chemical evolution of biomolecules. Full article

The RNA world hypothesis suggests that chemical networks consisting of functional RNA molecules could have constructed a primitive life-like system leading a first living system. The chemical evolution scenario of RNA molecules should be consistent with the Hadean Earth environment. We have demonstrated the importance of the environment at both high temperature and high pressure, using different types of hydrothermal flow reactor systems and high-pressure equipment. In the present study, we have attempted to develop an alternative easy-to-implement method for high-pressure measurements and demonstrate that the system is applicable as an efficient research tool for high-pressure experiments at pressures up to 30 MPa. We demonstrate the usefulness of the system by detecting the high-pressure influence for the self-cleavage of avocado hammerhead ribozyme (ASBVd(−):HHR) at 45–65 °C. A kinetic analysis of the high-pressure behavior of ASBVd(−):HHR shows that the ribozyme is active at 30 MPa and its activity is sensitive to pressures between 0.1–30 MPa. The surprising finding that such a short ribozyme is effective for self-cleavage at a high pressure suggests the importance of pressure as a factor for selection of adaptable RNA molecules towards an RNA-based life-like system in the Hadean Earth environment deep in the ocean. Full article

The origin of life might be sparked by the polymerization of the first RNA molecules in Darwinian ponds during wet-dry cycles. The key life-building block ribose was found in carbonaceous chondrites. Its exogenous delivery onto the Hadean Earth could be a crucial step toward the emergence of the RNA world. Here, we investigate the formation of ribose through a simplified version of the formose reaction inside carbonaceous chondrite parent bodies. Following up on our previous studies regarding nucleobases with the same coupled physico-chemical model, we calculate the abundance of ribose within planetesimals of different sizes and heating histories. We perform laboratory experiments using catalysts present in carbonaceous chondrites to infer the yield of ribose among all pentoses (5Cs) forming during the formose reaction. These laboratory yields are used to tune our theoretical model that can only predict the total abundance of 5Cs. We found that the calculated abundances of ribose were similar to the ones measured in carbonaceous chondrites. We discuss the possibilities of chemical decomposition and preservation of ribose and derived constraints on time and location in planetesimals. In conclusion, the aqueous formose reaction might produce most of the ribose in carbonaceous chondrites. Together with our previous studies on nucleobases, we found that life-building blocks of the RNA world could be synthesized inside parent bodies and later delivered onto the early Earth. Full article