Possible role of volcanic ash-gas clouds in the Earth's prebiotic chemistry

A Prebiotic Precursor to Life's Phosphate Transfer System with an ATP Analog and Histidyl Peptide Organocatalysts

Biochemistry is dependent upon enzyme catalysts accelerating key reactions. At the origin of life, prebiotic chemistry must have incorporated catalytic reactions. While this would have yielded much needed amplification of certain reaction products, it would come at the possible cost of rapidly depleting the high energy molecules that acted as chemical fuels. Biochemistry solves this problem by combining kinetically stable and thermodynamically activated molecules (e.g., ATP) with enzyme catalysts. Here, we demonstrate a prebiotic phosphate transfer system involving an ATP analog (imidazole phosphate) and histidyl peptides, which function as organocatalytic enzyme analogs. We demonstrate that histidyl peptides catalyze phosphorylations via a phosphorylated histidyl intermediate. We integrate these histidyl-catalyzed phosphorylations into a complete prebiotic scenario whereby inorganic phosphate is incorporated into organic compounds though physicochemical wet-dry cycles. Our work demonstrates a plausible system for the catalyzed production of phosphorylated compounds on the early Earth and how organocatalytic peptides, as enzyme precursors, could have played an important role in this.

Sources of Nitrogen-, Sulfur-, and Phosphorus-Containing Feedstocks for Prebiotic Chemistry in the Planetary Environment

Biochemistry on Earth makes use of the key elements carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (or CHONPS). Chemically accessible molecules containing these key elements would presumably have been necessary for prebiotic chemistry and the origins of life on Earth. For example, feedstock molecules including fixed nitrogen (e.g., ammonia, nitrite, nitrate), accessible forms of phosphorus (e.g., phosphate, phosphite, etc.), and sources of sulfur (e.g., sulfide, sulfite) may have been necessary for the origins of life, given the biochemistry seen in Earth life today. This review describes potential sources of nitrogen-, sulfur-, and phosphorus-containing molecules in the context of planetary environments. For the early Earth, such considerations may be able to aid in the understanding of our own origins. Additionally, as we learn more about potential environments on other planets (for example, with upcoming next-generation telescope observations or new missions to explore other bodies in our Solar System), evaluating potential sources for elements necessary for life (as we know it) can help constrain the potential habitability of these worlds.

The Influence of Mineral Matrices on the Thermal Behavior of Glycine

On the Hadean-Early Archean Earth, the first islands must have provided hot and dry environments for abiotically formed organic molecules. The heat sources, mainly volcanism and meteorite impacts, were also available on Mars during the Noachian period. In recent work simulating this scenario, we have shown that neat glycine forms a black, sparingly water-soluble polymer ("thermomelanoid") when dry-heated at 200 °C under pure nitrogen. The present study explores whether relevant minerals and mineral mixtures can change this thermal behavior. Most experiments were conducted at 200 or 250 °C for 2 or 7 days. The mineral matrices used were phyllosilicates (Ca-montmorillonites SAz-1 and STx-1, Na-montmorillonite SAz-1-Na, nontronite NAu-1, kaolinite KGa-1), salts (NaCl, NaCl-KCl, CaCl2, artificial sea salt, gypsum, magnesite), picritic basalt, and three Martian regolith simulants (P-MRS, S-MRS, JSC Mars-1A). The main analytical method employed was high-performance liquid chromatography (HPLC). Glycine intercalated in SAz-1 and SAz-1-Na was well protected against thermomelanoid formation and sublimation at 200 °C: after 2 days, 95 and 79 %, respectively, had either survived unaltered or been transformed into the cyclic dipeptide (DKP) and linear peptides up to Gly6. The glycine survival rate followed the order SAz-1 > SAz-1-Na > STx-1 ≈ NAu-1 > KGa-1. Very good protection was also provided by artificial sea salt (84 % unaltered glycine after 200 °C for 7 days). P-MRS promoted the condensation up to Gly6, consistent with its high phyllosilicate content. The remaining matrices were less effective in preserving glycine as such or as peptides.

Occurrence of Tourmaline in Metasedimentary Rocks of the Isua Supracrustal Belt, Greenland: Implications for Ribose Stabilization in Hadean Marine Sediments

Abiotic formation of RNA was important for the emergence of terrestrial life, but the acknowledged difficulties of generating and stabilizing ribose have often raised questions regarding how the first RNA might have formed. Previous researchers have proposed that borate could have stabilized ribose; however, the availability of borate on the early Earth has been the subject of intense debate. In order to examine whether borate was available on the early Earth, this study examined metasedimentary rocks from the Isua Supracrustal Belt. Garnet, biotite, and quartz comprise the major constituents of the examined rocks. Field relationships and the chemical compositions of the examined rocks suggest sedimentary origin. The present study found that garnet crystals contain a number of inclusions of tourmaline (a type of borosilicate mineral). All tourmaline crystals are Fe-rich and categorized as schorl. Both garnet and tourmaline often contain graphite inclusions and this close association of tourmaline with garnet and graphite has not been recognized previously. Garnet-biotite and graphite geothermometers suggest that the tourmaline in garnet experienced peak metamorphic conditions (~500 °C and 5 kbar). The mineralogical characteristics of the tourmaline and the whole rock composition indicate that the tourmaline formed authigenically in the sediment during diagenesis and/or early metamorphism. Clay minerals in modern sediments have the capability to adsorb and concentrate borate, which could lead to boron enrichment during diagenesis, followed by tourmaline formation under metamorphic conditions. Clay minerals, deposited on the early Archean seafloor, were the precursors of the garnet and biotite in the examined samples. The studied tourmaline crystals were most likely formed in the same way as modern tourmaline in marine sediments. Therefore, boron enrichment by clays must have been possible even during the early Archean. Thus, similar enrichment could have been possible during the Hadean, providing a stabilization agent for ribose.

A possible prebiotic origin on volcanic islands of oligopyrrole-type photopigments and electron transfer cofactors

Tetrapyrroles are essential to basic biochemical processes such as electron transfer and photosynthesis. However, it is not known whether these evolutionary old molecules have a prebiotic origin. We have serendipitously obtained pyrroles, which are the corresponding monomers, in laboratory experiments that simulated the interaction of amino acid-containing seawater with molten lava. The thermal pyrrole formation from amino acids, which so far has only been reported for special cases, can be explained by the observation that the amino acids become metal bonded, for example in (CaCl2)3(Hala)2·6H2O (Hala=DL-alanine), when the seawater evaporates. At a few hundred degrees Celsius, sea salt crusts also release hydrochloric acid (HCl). On primordial volcanic islands, the volatile pyrroles and HCl must have condensed at cooler locations, for example, in rock pools. There, pyrrole oligomerization may have occurred. To study this possibility, we added formaldehyde and nitrite, two species for which plausible prebiotic sources are known, to 2,4-diethylpyrrole and HCl. We found that even at high dilution conjugated (oxidized) oligomers, including octaethylporphyrin and other cyclic and open-chain tetrapyrroles, were formed. All experiments were conducted under rigorously oxygen-free conditions. Our results suggest that primitive versions of present-day biological cofactors such as chlorophylls, bilins, and heme were spontaneously abiotically synthesized on primordial volcanic islands and thus may have been available to the first protocells.

Inversion concept of the origin of life

The essence of the inversion concept of the origin of life can be narrowed down to the following theses: 1) thermodynamic inversion is the key transformation of prebiotic microsystems leading to their transition into primary forms of life; 2) this transformation might occur only in the microsystems oscillating around the bifurcation point under far-from-equilibrium conditions. The transformation consists in the inversion of the balance "free energy contribution / entropy contribution", from negative to positive values. At the inversion moment the microsystem radically reorganizes in accordance with the new negentropy (i.e. biological) way of organization. According to this approach, the origin-of-life process on the early Earth took place in the fluctuating hydrothermal medium. The process occurred in two successive stages: a) spontaneous self-assembly of initial three-dimensional prebiotic microsystems composed mainly of hydrocarbons, lipids and simple amino acids, or their precursors, within the temperature interval of 100-300°C (prebiotic stage); b) non-spontaneous synthesis of sugars, ATP and nucleic acids started at the inversion moment under the temperature 70-100°C (biotic stage). Macro- and microfluctuations of thermodynamic and physico-chemical parameters able to sustain this way of chemical conversion have been detected in several contemporary hydrothermal systems. A minimal self-sufficient unit of life on the early Earth was a community of simplest microorganisms (not a separate microorganism).

Precambrian lunar volcanic protolife

Five representative terrestrial analogs of lunar craters are detailed relevant to Precambrian fumarolic activity. Fumarolic fluids contain the ingredients for protolife. Energy sources to derive formaldehyde, amino acids and related compounds could be by flow charging, charge separation and volcanic shock. With no photodecomposition in shadow, most fumarolic fluids at 40 K would persist over geologically long time periods. Relatively abundant tungsten would permit creation of critical enzymes, Fischer-Tropsch reactions could form polycyclic aromatic hydrocarbons and soluble volcanic polyphosphates would enable assembly of nucleic acids. Fumarolic stimuli factors are described. Orbital and lander sensors specific to protolife exploration including combined Raman/laser-induced breakdown spectrocsopy are evaluated.

Production of low molecular weight hydrocarbons by volcanic eruptions on early Mars

Methane and other larger hydrocarbons have been proposed as possible greenhouse gases on early Mars. In this work we explore if volcanic processes may have been a source for such molecules based on theoretical and experimental considerations. Geologic evidence and numerical simulations indicate that explosive volcanism was widely distributed throughout Mars. Volcanic lightning is typically produced in such explosive volcanism. Therefore this geologic setting was studied to determine if lightning could be a source for hydrocarbons in volcanic plumes. Volcanic lightning was simulated by focusing a high-energy infrared laser beam inside of a Pyrex reactor that contained the proposed volcanic gas mixture composed of 64% CH(4), 24% H(2), 10% H(2)O and 2% N(2), according to an accretion model and the nitrogen content measured in Martian meteorites. The analysis of products was performed by gas chromatography coupled to infrared and mass spectroscopy. Eleven hydrocarbons were identified among the products, of which acetylene (C(2)H(2)) was the most abundant. A thermochemical model was used to determine which hydrocarbons could arise only from volcanic heat. In this case, acetylene and ethylene are formed at magmatic temperatures. Our results indicate that explosive volcanism may have injected into the atmosphere of early Mars approximately 6 x 10(12) g yr(-1) of acetylene, and approximately 2 x 10(12) g yr(-1) of 1,3-butadiyne, both produced by volcanic lightning, approximately 5 x 10(11) g yr(-1) of ethylene produced by volcanic heat, and 10(13) g yr(-1) of methane.

A thermodynamic assessment of the potential synthesis of condensed hydrocarbons during cooling and dilution of volcanic gases

The possibility for abiotic synthesis of condensed hydrocarbons in cooling/diluting terrestrial volcanic gases has been evaluated on the basis of the consideration of metastable chemical equilibria involving gaseous CO, CO2, H2 and H2O. The stabilities of n-alkanes and polycyclic aromatic hydrocarbons (PAHS) have been evaluated for several typical volcanic gas compositions under various conditions for cooling/diluting of quenched volcanic gas. The modeling shows that n-alkanes and PAHs have a thermodynamic potential to form metastably from H2 and CO below approximately 250 degrees C within the stability field of graphite. Despite the predominance of CO2 in volcanic gases, synthesis of hydrocarbons from CO2 and H2 is less favored energetically than from CO and H2. Both low temperature and a high H/C atomic ratio in volcanic gas generally favor stability of hydrocarbons with higher H/C ratios. PAHs are thermodynamically stable at temperatures approximately 10 degrees -50 degrees C higher than large n-alkanes; however, at lower temperatures, PAHs and n-alkanes have similar stabilities and are likely to form metastable mixtures. Both the energetic drive to form hydrocarbons and possible temperatures of formation increase as the oxidation state (fO2) of the volcanic gases decreases and as the cooling/dilution ratios of volcanic gases increase. Synthesis of hydrocarbons is energetically more likely in cooling trapped gases than in ashcloud eruptive columns. Mechanisms for hydrocarbon formation may include Fischer-Tropsch-type synthesis catalyzed by magnetite from solid volcanic products. On the early Earth, Mars, and Jupiter's satellite Europa, several factors would have provided more favorable conditions for hydrocarbon synthesis in volcanic gases than under current terrestrial conditions and might have contributed to the production of organic compounds required for the emergence of life.

Chemical reduction of phosphate on the primitive earth

If phosphorus played a role in the origin of life, some means of concentrating micromolar levels of phosphate (derived from the calcium phosphate mineral apatite), must first have been available. Here we show that simulated (mini)lightning discharges in model prebiotic atmospheres, including only minimally reducing ones, reduce orthophosphates, including apatite, to produce substantial yields of phosphite. Electrical discharges associated with volcanic eruptions could have provided a particularly suitable environment for this process. Production of relatively soluble and reactive phosphite salts could have supplied a pathway by which the first phosphorus atoms were incorporated into (pre)biological systems.

Behavior of amino acids when volatilized in the presence of silica gel and pulverized basaltic lava

To evaluate the types of amino acid thermal transformations caused by silicate materials, we studied the volatilization products of Aib, L-Ala, L-Val and L-Leu under temperatures of up to 270 degrees C in the presence of silica gel as a model catalyst and pulverized basaltic lava samples. It was found that silica gel catalyzes nearly quantitative condensation of amino acids, where piperazinediones are the major products, whereas lava samples have much lower catalytic efficiency. In addition bicyclic and tricyclic amidines and several products of their subsequent thermal decomposition have been identified using the coupled technique of GC-FTIR-MS and HPLC-PB-MS, with auxiliary computer simulation of IR spectra and NMR spectroscopy. The decomposition is due to dehydrogenation, elimination of the alkyl substituents and dehydration as well as cleavage of the bicyclic ring system. The imidazole ring appears to be more resistant to thermal decomposition as compared to the pyperazine moiety, giving rise to the formation of different substituted imidazolones. The amidines were found to hydrolyze under treatment with concentrated HCl, releasing the starting amino acids and thus behaving as amino acid anhydrides. The thermal transformations cause significant racemization of amino acid residues. Based on our observations, the formation of amidine-type products is suggested to be rather common in the high-temperature experiments on amino acid condensation.

Biochemical evolution. I. Polymerization On internal, organophilic silica surfaces of dealuminated zeolites and feldspars

Catalysis at mineral surfaces might generate replicating biopolymers from simple chemicals supplied by meteorites, volcanic gases, and photochemical gas reactions. Many ideas are implausible in detail because the proposed mineral surfaces strongly prefer water and other ionic species to organic ones. The molecular sieve silicalite (Union Carbide; = Al-free Mobil ZSM-5 zeolite) has a three-dimensional, 10-ring channel system whose electrically neutral Si-O surface strongly adsorbs organic species over water. Three -O-Si tetrahedral bonds lie in the surface, and the fourth Si-O points inwards. In contrast, the outward Si-OH of simple quartz and feldspar crystals generates their ionic organophobicity. The ZSM-5-type zeolite mutinaite occurs in Antarctica with boggsite and tschernichite (Al-analog of Mobil Beta). Archean mutinaite might have become de-aluminated toward silicalite during hot/cold/wet/dry cycles. Catalytic activity of silicalite increases linearly with Al-OH substitution for Si, and Al atoms tend to avoid each other. Adjacent organophilic and catalytic Al-OH regions in nanometer channels might have scavenged organic species for catalytic assembly into specific polymers protected from prompt photochemical destruction. Polymer migration along weathered silicic surfaces of micrometer-wide channels of feldspars might have led to assembly of replicating catalytic biomolecules and perhaps primitive cellular organisms. Silica-rich volcanic glasses should have been abundant on the early Earth, ready for crystallization into zeolites and feldspars, as in present continental basins. Abundant chert from weakly metamorphosed Archaean rocks might retain microscopic clues to the proposed mineral adsorbent/catalysts. Other framework silicas are possible, including ones with laevo/dextro one-dimensional channels. Organic molecules, transition-metal ions, and P occur inside modern feldspars.