The biological cosmological constant ΛB: Exploratory propensity, dynamical habitability and the geometric origin of life.

The stability of nucleic acids under ultraviolet (UV) irradiation was key to the persistence of life on Earth. Among the canonical nucleobases, pyrimidines are most susceptible to UV photodamage, yielding cyclobutane pyrimidine dimers (CPDs) that distort nucleic acid conformation and interfere with function. Prior to the emergence of enzymatic CPD repair, intrinsic processes like UV-induced self-repair may have influenced the survival of ancient nucleic acids in high-UV early Earth environments. Our previous work reported self-repair quantum yields for the canonical CPD-containing RNA sequence GAU=U (0.23%), and the DNA sequence d(GAT=T) (0.44%), but the origin of the disparity is unclear. Here, we address this missing link experimentally by measuring the self-repair of the chimeric CPD-containing sequence d(GAU=U) to d(GAUU) using UV/Vis spectroscopy and HPLC analysis. Upon irradiation at 285 nm, its repair quantum yield (1.16%) exceeded the repair yields of GAU=U, d(GAT=T), and T=TAG, as well as the reported CPD formation yields in UU. We measured damage formation in d(UU) and found a damage quantum yield of 0.74%, demonstrating that d(GAUU), to our knowledge, is the first reported oligonucleotide in which the self-repair quantum yield exceeds the measured net damage quantum yield under identical irradiation conditions. These results highlight the combined importance of backbone conformation and sequence in governing self-repair and suggest that chimeric sequences may have been especially UV-resistant precursors to canonical DNA.

The most commonly accepted scenario of early Earth includes: creation of the universe around 13.8 Ga (Giga-annus; or 109 years ago); establishment of our solar system ~ 4.60 Ga; and formation of Earth ~ 4.54 Ga. The earliest life forms on our planet so far observed to have existed, are microbes that left signals of their presence in rocks ~ 3.6 Ga - suggesting that Life forms existed within the first 940million years after Earth's formation. However, an intriguing recent publication [1] infers that the last universal common ancestor (LUCA) likely existed by 4.2 Ga, and that the inferred LUCA had a genome of at least 2.5Mb of DNA, encoding around 2,600 proteins; this suggests that sophisticated Life might have existed within the first 340million years after Earth was formed. The commonly accepted geological history of early Earth suggests that the turbulent Hadean Eon lasted until 4.0 Ga, with the Late Heavy Bombardment (LHB) period occurring around 4.1 to 3.8 Ga. If Earth during the Hadean exhibited a molten surface, intense volcanic activity, and constant bombardment by asteroids and comets - how were sensitive molecules (e.g., nucleic acids, proteins) able to survive? Considering the "Lipid First" hypothesis [2], we propose that replicating lipid micelles are feasible candidates for having populated much of Earth's deep hydrothermal vents and turbulent surface within the first 340million years of Earth's existence. These lipid micelles could therefore have provided a plausible form of "protective capsules" inside which early Life's sensitive molecules were able to evolve.

Questions about our earliest beginnings have filled thinking minds for millennia across cultures, faiths, and wide-ranging frontiers of research. Asking where we come from is as fundamental as astrobiology's driving query of "are we alone?" These days, we often link these questions as we explore life beyond our planet and solar system. Scientific steps toward answers have been big and frequent, but the pathways remain highly varied. Achieving something even close to a consensus has been elusive. The one thing we all can agree on, however, is that our understanding of Earth's earliest stages, and that of our solar system, has advanced by leaps and bounds over recent decades. No longer must we explore life's beginnings with little knowledge of how and when planetary habitability first developed and, more specifically, what the world was like roughly 4.4-4.2 billion years ago-a reasonable time estimate for the initial steps in the progression toward life. The simple distillation of this view is that models for life's earliest chapters, including experimental simulations of prebiotic chemistry, can and should be designed around an increasingly sophisticated understanding of Earth's initial boundary conditions, including the timing and controls on the emergence of oceans, the atmosphere, and tectonics-along with their coupled evolutions.

This review of martian organic geochemistry aims to contextualize recent findings of organic molecules in martian meteorites and from Mars missions within the broader study of origins of life on Earth. Analyzing martian organic inventories helps us understand the abiotic processes in planetary environments that are common wherever rocks interact with liquid brines and that likely contributed to the emergence of life on Earth. Mars is only the second planetary body studied for organic molecules; while carbonaceous meteorites, comet missions, and sample-return analyses of comets and asteroids have shown the diversity of organics across the solar system, studying Mars reveals what these molecules are on another planet. Although a definitive sign of extraterrestrial life has not yet been found, the findings provide insights into abiotic synthesis mechanisms that would have occurred on early Earth. At worst, these observations represent the oldest planetary record of organic and prebiotic chemical synthesis pathways that could have led to life, as inferred from the alteration of Earth's oldest rocks. They may also point to potential habitats for past martian life. Currently, samples collected by the Perseverance rover represent a unique opportunity to verify which of the two questions, "Are we alone?" or "How did we get here?" will be true for Mars. Without doubt, these questions would be best addressed through the use of higher resolution analyses by more advanced and sensitive instrumentation after sample return to Earth. Even if no definitive signs of life are found in returned samples, they would give us the opportunity to study the missing link to life on Earth, that of the primordial abiotic organic chemical processes that could have led to life. Therefore, there are no wrong answers to exploring Mars for signs of life; its secrets will illuminate our understanding of ourselves and our place in the universe, whatever the answer.

To address the chemistry responsible for life's emergence, we examine the simple chemicals accessible on early Earth and the processes that could have transformed them. We focus on carbon reduction as a process central to the direct precursors of life. Two main approaches for the emergence of life's building blocks and their associated functions are discussed. One approach investigates chemical routes for forming life's building blocks via processes that worked differently from those of extant life, referred to as "unrestricted" prebiotic chemistries. The other approach establishes a direct mechanistic connection between prebiotic building blocks and extant biochemistry, referred to as "lifelike" prebiotic chemistries. Significant gaps remain in our understanding of early Earth's conditions, which makes it difficult to constrain the possible locations and mechanisms of life's emergence and the sources of precursors. Although numerous differences remain between the main origin-of-life hypotheses, consideration of the geochemistry of carbon reduction is a common denominator of these historically divided hypotheses.

Formation and spontaneous oxidation of neutral [4Fe-4S] clusters in prebiotic oceans.

Membrane-free coacervates, typically formed through electrostatic interactions between oppositely charged polyelectrolytes, have been extensively utilized as artificial life-like systems in protocell research, providing valuable insights into the origin of life. However, considering that inorganic metal ions may have been more abundant under early Earth conditions, it is plausible that these metal ions played a significant role in prebiotic compartmentalization. In this study, we present a novel coacervate protocell formed via liquid-liquid phase separation (LLPS) of simple anionic polypeptides, induced by electrostatic and coordination interactions with inorganic metal cations, using divalent zinc ions as a specific example due to their prebiotic availability and biological relevance. The peptide-zinc ion coacervate microdroplet exhibits liquid-like properties, client partitioning, and enhanced catalysis comparable to those of typical polyelectrolyte coacervates. By integrating experimental results and theoretical simulations, we identify two kinetic pathways to phase separation mediated by the coordination mode at varying zinc ion concentrations, resulting in the formation of nonequilibrium gel-like condensates or droplets that further contribute to distinct light-induced catalytic efficiency. Overall, our work highlights that peptide-metal ion interaction-driven compartmentalization, as prebiotic microreactors, could have facilitated primitive biochemical reactions on early Earth, thus offering a plausible and diverse pathway for the emergence of protocells.

Manganese oxides, thought to form almost exclusively through reactions between Mn2+ and O2, catalyze oxidative transformations among redox-sensitive metals. Thus, the occurrence of Mn oxides, either observed or inferred from sedimentary geochemical data, has formed the basis for multiple hypotheses concerning the evolution of the atmospheric redox state on the early Earth and Mars. Here, using theory and experiments, we report that the band gap of common Ca/Mg carbonate minerals (including calcite, magnesite, and aragonite) is significantly lowered by trace incorporation (0.8 wt% or lower) of Mn(II) into their bulk structure or surface, conferring photochemical reactivity under ultraviolet conditions relevant to early Earth and Mars (200 to 400 nm). Moreover, we show that surface incorporation of Mn(II) reduces the fundamental band gap much more effectively (by >1 eV) than bulk incorporation. Our results suggest that photo-oxidation of Mn(II)-bearing carbonates could have occurred widely on planetary surfaces, resulting in the abiotic formation of manganese oxides without free molecular oxygen. Photochemically driven redox cycling of manganese could help sustain redox disequilibria for microbial metabolisms, but compromises the use of manganese oxides as oxygen barometers.

Calcium silicate perovskite (CaPv) is the host for many trace elements in the lower mantle. Whether, when, and where it forms during the solidification of the magma ocean is fundamental to understanding the geochemical and geodynamical evolution of the early Earth. We performed first-principles molecular dynamics simulations to investigate the partitioning of Ca (alongside Sr and Ba) between bridgmanite and molten pyrolite and laser-heated diamond anvil cell experiments to replicate the crystallization of pyrolitic melt. Results show that Ca is incompatible in bridgmanite at all relevant crystallization conditions in the lower mantle, indicating a progressive enrichment of Ca in the magma ocean as it solidifies. This leads to the crystallization of CaPv during the final stages of solidification in the deep mantle. Coupled with the low bridgmanite-melt partition coefficients for Sr and Ba, our findings infer that both large ion lithophile elements and their host, CaPv, will be concentrated in the deep mantle at the end of magma ocean solidification.

The biological significance of the transition metal molybdenum (Mo) lies in its function at the catalytic center of several enzymes that drive a wide spectrum of redox reactions underlying global biogeochemical cycles, yet a paradox persists. While modern life ubiquitously relies on Mo, geochemical evidence suggests that its availability in early Earth's anoxic oceans was extremely limited. Modern organisms can use Mo down to trace levels; however, the rates of Mo-dependent metabolisms slow down when Mo availability decreases, posing fundamental questions about the extent to which changing Mo abundances shaped the evolution of molybdoenzymes, and when early life began harnessing Mo. Here, we confront this evolutionary enigma by reconstructing the temporal and ecological emergence of molybdoenzymes, their transport systems, and biosynthetic pathways. In parallel, we examine biological tungsten (W) usage due to shared chemical properties and cofactor biosynthetic pathways with Mo. We provide molecular dating evidence of Mo/W utilization back to the Eo- to Mesoarchean (~3.7-3.1 Ga). These findings challenge prevailing assumptions about trace metal availability on the early Earth and underscore the profound antiquity and adaptability of Mo-based biochemistry in shaping early microbial evolution.

Responsible for fixing 25% of carbon dioxide (CO2) globally, cyanobacteria use carboxysomes to house their CO2 fixing machinery. The formation and permeability of the proteinaceous shell of carboxysomes is an area of active study. While necessary in air (0.04% CO2), the shell is not required when cyanobacteria are in high CO2 levels representative of early Earth. To understand how the carboxysome shell responds to increased CO2 conditions, we used a Grx1-roGFP2 redox sensor and single cell timelapse fluorescence microscopy to track subcellular redox states of Synechococcus sp. PCC 7002. Comparing different levels of compartmentalization, we targeted the cytosol, a shell-less carboxysomal assembly intermediate called procarboxysomes, and carboxysomes. Carboxysome redox state was dynamic, and, under 3% CO2 conditions, procarboxysome-like structures formed which were only partially encapsulated and exposed the carboxysome contents to the cytosol. This work expands the adaptability of carboxysomes to environmental conditions and builds understanding of the selective forces that initially drove carboxysome evolution.

Prebiotic oligomerization of amino acids: A step in molecular evolution toward biological complexity.

Coacervate dropletsand lipid vesicles are two classes of self-assembledcompartments that have been proposed as protocell models. Hybrid protocells,in which a coacervate core is surrounded by a lipid membrane, canintegrate the advantages of both protocell systems while overcomingtheir limitations. Although hybrid protocell membranes have been producedwith a variety of diacyl phospholipids related to modern biology andsome single-chain amphiphiles inspired by prebiotic scenarios, littleis known about how mixtures of single-chain amphiphiles impact hybridprotocell membrane formation and properties. Given the plausible diversityof amphiphiles in the prebiotic milieu, the resulting membranes wouldhave inherently incorporated multiple lipids of different types, potentiallyaltering the properties and viability of hybrid protocells in theirenvironment. Here, we systematically increased the compositional heterogeneityof hybrid protocell membranes by using different prebiotically relevantsingle-chain amphiphiles of varying head groups and alkyl chain lengths.These membranes were assembled around model coacervate droplets generatedfrom poly­(allylamine hydrochloride) and adenosine diphosphate, andthe effect of heterogeneity on membrane properties and stability wasevaluated. Compared to protocells with homogeneous membranes, thosewith heterogeneous amphiphile membranes exhibited higher yields, smallersizes, and greater subcompartment formation. Also, they showed increasedmembrane order, retained similar lateral lipid diffusion, and showedpopulation-level variability in permeability to small anionic molecules.Notably, heterogeneous membranes showed enhanced structural stabilityunder acidic conditions, retaining key properties like size and subcompartmentheterogeneity, thereby broadening the pH range over which hybrid protocellsremain intact. These findings suggest that amphiphile diversity notonly would have influenced the structural properties of hybrid protocellsbut also created diversity within the protocell population and enhancedtheir robustness, thereby playing a crucial role in protocell evolutionon early Earth.

El Niño events recorded by redox sensitive trace elements in sedimentary records from Genovesa Lake, Galápagos.

Two fundamental questions have puzzled scientists for more than 150 years. "How did life become homochiral?" and "why was this specific handedness selected?" Recently, it has been shown that homochirality could have emerged through the enantioselective interactions of molecules with magnetic substrates due to the asymmetric crystallization of an RNA precursor on a magnetite substrate, abundant on early Earth. This phenomenon is based on the chirality-induced spin selectivity (CISS) effect. Despite its robustness, this model could not provide an answer to the second question: Why one specific handedness (D for RNA) was selected. Here, we demonstrate that spin-involving processes can have different outcomes in the two enantiomers of chiral molecules. In chiral molecules with unpaired electrons or while electrons are passing through them, the total angular momentum vector, J, is aligned along the "easy axis," which is defined by the magnetic anisotropy induced by the spin-orbit coupling and asymmetry of the molecular field. The magnitude J is the same for both enantiomers, but the vectors may be aligned differently relative to the molecular frame in the two enantiomers. This difference can be quantified by, for example, by the angle between J and electric dipole moment of the molecule, μ. We show by direct measurements, theory, and ab initio calculations that dynamic spin processes in chiral molecules could result in different efficiencies of spin-related phenomena, including the interaction of chiral molecules with magnetic surfaces. The findings may provide an explanation for the specific homochirality in nature.

Abstract The emergence of habitable conditions on the early Earth and on rocky exoplanets requires persistent energy sources that can drive both prebiotic chemistry and climate warming under magnetically active young G–M stars. To quantify the contribution of stellar energetic particle (StEP) events associated with superflares to the atmospheric chemistry of young planets with primitive atmospheres, we carried out a suite of laboratory proton-irradiation experiments on mildly reduced gas mixtures. We present first proton irradiation experiments of N 2 –CO 2 –rich gas mixtures that yield abundant nitrous oxide (N 2 O) at mixing ratios up to ∼10 3 ppmv, together with amino acid precursors including glycine, corresponding to global production rates of order 2 × 10 10 kg yr −1 on the early Earth. Our photochemical modeling of StEP-driven proton irradiation reproduces the experimentally inferred N 2 O production rates and provides self-consistent atmospheric N 2 O profiles. We then use these profiles of N 2 O as input to a 3D global climate model to evaluate the radiative–climatic impact of StEP-generated N 2 O in primitive atmospheres representative of the early Earth and young rocky exoplanets. Our results show that frequent StEP events can help alleviate the faint young Sun paradox on the early Earth and can maintain temperate surface conditions on young rocky exoplanets beyond the outer edges of the habitable zone, while simultaneously enhancing the buildup of prebiotic molecules. Together, these processes may constitute a robust pathway toward early planetary habitability.

Many petrological, geodynamical, and geochemical perspectives have offered circumstantial evidence for either an early onset of plate tectonics in the first 10% of Earth's history or a late onset after the great oxidation event (2.5 Ga ago). This calls into question over what timescales plate tectonics have influenced terrestrial geological and geochemical processes. We present geochemical data from the products of ancient crustal subduction, which were recycled into the deep mantle and then tapped by the modern Marquesas volcanic hotspot. We demonstrate that these materials have distinct short-lived radiogenic (146Sm-142Nd, t1/2 = 103 Ma) isotopic compositions (average μ142Nd = +2.3 ±1.3, n = 3) compared to other Marquesas lavas (average μ142Nd = -0.8 ±1.2, n = 7). These results require that the history of these subduction products diverged from those of other Marquesas magmas more than four billion years ago. Quantitative modeling suggests that the most geochemically enriched Marquesas samples represent up to ~0.6% recycled crustal sediments, which may have been subducted at any time in Earth's history but were most likely subducted in the late Hadean Eon to early Eoarchean Era. The inferred felsic composition of such materials further requires that both crustal melting and sedimentation processes were active in some form on the early Earth. Further, the preservation of evidence for foundational planetary events in geologically young rocks reveals that Earth's volcanic hotspots could provide a defining perspective on the early planetary-scale processes that build Earth-like planets.

Abstract Understanding asteroid-collision-generated extreme environments, including hydrothermal activity, is crucial for gaining insights into biological evolution on the early Earth. Here, we demonstrate that stromatolites—the oldest fossil evidence of oxygen-producing microbial life on early Earth—could have developed within impact craters, based on a detailed investigation of stromatolites and lake sediments in the Hapcheon impact crater, Korea. Our study revealed that the Hapcheon impact event occurred 42,300 ± 1000 years before the present (cal yr BP) from radiocarbon ages of charcoals included in the impact breccias at 100 ~ 140 m depth underground, and stromatolites formed at the lake margin under the post-impact hydrothermal conditions, as indicated by positive Europium anomaly in the stromatolites. Furthermore, significantly depleted Osmium isotope ratios in the stromatolites support the possible meteoritic influence. Considering the frequency of asteroid collisions during the early Earth, stromatolite blooms in impact craters could be one of the active oxygen oases that led to the creation of habitable environments on the early Earth.

From early Earth to Enceladus-mineral electrochemistry could drive organic synthesis.