Origins of Life and Evolution of the Biosphere

Decorated vesicles in deep, seafloor basalts form abiotically, but show at least four life-analogous features, which makes them a candidate for origin of life research. These features are a physical enclosure, carbon-assimilatory catalysts, semi-permeable boundaries, and a source of usable energy. The nanometer-to-micron-sized spherules on the inner walls of decorated vesicles are proposed to function as mineral proto-enzymes. Chemically, these structures resemble synthetic FeS clusters shown to convert CO2 , CO and H2 into methane, formate, and acetate...

The dynamic behaviors of prebiotic reaction networks may be critically important to understanding how larger biopolymers could emerge, despite being unfavorable to form in water. We focus on understanding the dynamics of simple systems, prior to the emergence of replication mechanisms, and what role they may have played in biopolymer formation. We specifically consider the dynamics in cyclic environments using both model and experimental data. Cyclic environmental conditions prevent a system from reaching thermodynamic equilibrium, improving the chance of observing interesting kinetic behaviors...

Some amino acids can crystallize from aqueous solution both as conglomerates and racemic compounds: under high supersaturation following rapid evaporation, dissolved amino acids draining over porous sand-bars behave like conglomerates whereas in the resulting deeper pool of water, amino acid solution switches to the more common racemic-compound system. We show how the two forms might have sequentially combined under prebiotic conditions to form the basis of homochirality. The paper is a quantitative analysis of enantiomeric excess (EE) this dual behavior of amino acids is capable of producing in tandem: Initial amplification by preferential crystallization (PC) in conglomerate system (CS) followed by further amplification in the racemic compound system (RCS)...

Thiocyanate may have played as important a role as cyanide in the synthesis of several molecules. However, its concentration in the seas of the prebiotic Earth could have been very low. Thiocyanate was dissolved in two different seawaters: a) a composition that comes close to the seawater of the prebiotic Earth (seawater-B, Ca2+ and Cl- ) and b) a seawater (seawater-A, Mg2+ and SO4 2- ) that could be related to the seas of Mars and other moons in the solar system. In addition, forsterite-91 was a very common mineral on the prebiotic Earth and Mars...

The present article reports Raman spectroscopic observations of siderite, hematite, disordered graphitic carbon and possibly greenalite inside the quartz matrix of a banded iron sample from the BARB3 core drilled inside the 3.4 Ga Buck Reef Chert of the Barberton Greenstone Belt in South Africa. The article also reports Raman spectroscopic observations of quartz cavities, concluding in the presence of water, methane and sodium hydroxide at high concentration leading to pH ~ 15 inside the inclusion, suggesting an Archean water which was strongly basic...

Enantiomers have a different energy due to the parity violation effects. Up to now, these effects are difficult to calculate and their final effect on the choice of one enantiomer in the homochirality issue is still a matter of debate. Nevertheless, many scientists support the role of this tiny energy difference in the triggering of homochirality. In this work, we studied the energy difference in atropisomers, a class of stereoisomers in which the chirality is given by the block of rotation around one bond...

While there is consensus that Archean atmosphere was anoxic with O2 pressure, p(O2 ) <10-6 PAL (present atmospheric level) at sea-level, evidence suggests that p(O2 ) at stratospheric altitudes of 10-50 km was orders of magnitude higher, a result of photodissociation of CO2 by UVC sunlight and incomplete mixing of O2 with other gases. Molecular O2 is paramagnetic due to triplet ground state. Magnetic circular dichroism (MCD) by stratospheric O2 is examined in earth's magnetic field and shows maximum circular polarization │(I+ - I- )│ at altitude of 15-30 km (I+ /I- is intensity of left/right circularly polarized light)...

RNA World Hypothesis is centred around the idea of a period in the early history of life's origin, wherein nonenzymatic oligomerization and replication of RNA resulted in functional ribozymes. Previous studies in this endeavour have demonstrated template-directed primer extension using chemically modified nucleotides and primers. Nonetheless, similar studies that used non-activated nucleotides led to the formation of RNA only with abasic sites. In this study, we report template-directed primer extension with prebiotically relevant cyclic nucleotides, under dehydration-rehydration (DH-RH) cycles occurring at high temperature (90 °C) and alkaline conditions (pH 8)...

It is common in origins of life research to view the first stages of life as the passive result of particular environmental conditions. This paper considers the alternative possibility: that the antecedents of life were already actively regulating their environment to maintain the conditions necessary for their own persistence. In support of this proposal, we describe 'viability-based behaviour': a way that simple entities can adaptively regulate their environment in response to their health, and in so doing, increase the likelihood of their survival...

Polyphosphate-mediated peptide bond formation is central to protein synthesis in modern organisms, but a simpler form of activation likely preceded the emergence of proteins and RNA. One suggested scenario involves trimetaphosphate (TP), an inorganic phosphate that promotes peptide condensation. Peptide bond formation can also be promoted by high pH and drying, but the interaction of these factors with TP has yet to be characterized kinetically. We studied the formation of glycine oligomers formed under initially alkaline conditions in the presence of TP during the process of drying...

We review the literature surrounding chiral symmetry-breaking in chemical systems, with a focus on understanding the mathematical models underlying these chemical processes. We comment in particular on the toy model of Sandars, Viedma's crystal grinding systems and the APED model. We include a few new results based on asymptotic analysis of the APED system.

The adsorption of thymine, a key pyrimidine base of deoxyribonucleic acid (DNA) on montmorillonite clay (Mnt) exchanged with metal ions (Mnt-M2+ , M2+  = Fe2+ , Co2+ , Cu2+ , Ca2+ , and Mg2+ ) over a range of concentration (7.0 × 10-5  M to 12.0 × 10-5  M) and pH (4.0 - 9.0) at ambient temperature has been investigated in aqueous environment spectrophotometrically (UV, FTIR, XRD, SEM-EDX). The effectiveness of various adsorbents was determined in terms of percent (%) binding and Langmuir constants (KL and Xm ) using Langmuir adsorption isotherm at their respective pH of maximum adsorption...

We study a very simple linear evolutionary model based on distribution of protocells by total enantiomeric excess and without any mutual inhibition and show that such model can produce two species with values of total enantiomeric excess in each of the species approaching [Formula: see text] when there is a global [Formula: see text] symmetry. We then consider a scenario when there is a small external global asymmetry factor, like weak interaction, and show that only one of the species remains in such a case, and that is the one, which is more efficient in replication...

Protein coordinated iron-sulfur clusters drive electron flow within metabolic pathways for organisms throughout the tree of life. It is not known how iron-sulfur clusters were first incorporated into proteins. Structural analogies to iron-sulfide minerals present on early Earth, suggest a connection in the evolution of both proteins and minerals. The availability of large protein and mineral crystallographic structure data sets, provides an opportunity to explore co-evolution of proteins and minerals on a large-scale using informatics approaches...

The origin of the genetic code is probably the central problem of the studies on the origin of life. The key question to answer is the molecular mechanism that allows the association of the amino acids with their triplet codons. We proposed that the codon-anticodon duplex located in the acceptor stem of primitive tRNAs would facilitate the chemical reactions required to synthesize cognate amino acids from simple amino acids (glycine, valine, and aspartic acid) linked to the 3' acceptor end. In our view, various nucleotide-A-derived cofactors (with reactive chemical groups) may be attached to the codon-anticodon duplex, which allows group-transferring reactions from cofactors to simple amino acids, thereby producing the final amino acid...

No abstract text is available yet for this article.

Most amino acids and sugar molecules occur in mirror, or chiral, images of each other, knowns as enantiomers. However, life on Earth is mostly homochiral: proteins contain almost exclusively L-amino acids, while only D-sugars appear in RNA and DNA. The mechanism behind this fundamental asymmetry of life remains unknown, despite much progress in the theoretical and experimental understanding of homochirality in the past decades. We review three potential mechanisms for the emergence of biological homochirality on primal Earth and explore their implications for astrobiology: the first, that biological homochirality is a stochastic process driven by local environmental fluctuations; the second, that it is driven by circularly-polarized ultraviolet radiation in star-forming regions; and the third, that it is driven by parity violation at the elementary particle level...

To understand chiral symmetry breaking on the molecular level, we developed a method to efficiently investigate reaction kinetics of single molecules. The model systems include autocatalysis as well as a reaction cascade to gain further insight into the prebiotic origin of homochirality. The simulated reactions start with a substrate and only a single catalyst molecule, and the occurrence of symmetry breaking was examined for its degree of dependence on randomness. The results demonstrate that interlocking processes, which e...

Biological homochirality of essential components such as L-amino acids and D-sugars is prerequisite for the emergence, evolution and the maintenance of life. Implication of biological homochirality is described. Considerable interest has been focused on the origin and the process leading to the homochirality. Asymmetric autocatalysis with amplification of enantiomeric excess (ee), i.e., the Soai reaction, is capable to link the low ee induced by the proposed origins of chirality such as circularly polarized light and high ee of the organic compound...

The Prebiotic Chemistry and Early Earth Environments (PCE3 ) Consortium is a community of researchers seeking to understand the origins of life on Earth and in the universe. PCE3 is one of five Research Coordination Networks (RCNs) within NASA's Astrobiology Program. Here we report on the inaugural PCE3 workshop, intended to cross-pollinate, transfer information, promote cooperation, break down disciplinary barriers, identify new directions, and foster collaborations. This workshop, entitled, "Building a New Foundation", was designed to propagate current knowledge, identify possibilities for multidisciplinary collaboration, and ultimately define paths for future collaborations...