Stochastic Prebiotic Chemistry within Realistic Geological Systems

Abstract

This review introduces its readers to a ‘stochastic approach’ to origins of life research, from the viewpoints of both prebiotic chemistry and geology. The idea of a “primordial soup” has been subject to extensive criticism from thermodynamic, biochemical and geochemical perspectives, yet recent advancements have made clearer the plausibility of this theory. Herein, we review the theoretical and experimental approaches which have previously been explored, among these modelling, laboratory‐confined and geologically motivated experimentation. Of these, we consider organo‐mineral interactions, uniting aspects of prebiotic chemistry and geology, to be an especially promising way forward. However, we aim here to advance current approaches by advocating a methodology involving chemical systems and their stochastic reactivity on heterogeneous geological surfaces. This models the origins of life as a continuity of chemical reactions in an analogue to the early Earth (Hadean) environment.

The Emergence of Life

“…Recently, emphasis has shifted towards furthering our understanding of non-enzymatic autocatalytic sets, since it is suspected that RNA may not have been able to orchestrate proto-metabolism on its own. In relation to this last point, it is becoming clearer that focusing on stochastic (or 'dirty') chemistry, where most relevant reactions coexist under similar reaction conditions, might represent a more accurate view of relevant prebiotic chemistry (Dass et al 2016;Guttenberg et al 2017), rather than the classic synthetic chemistry approach, which heavily relies on more unnatural sequences of very specific reaction conditions. Nonetheless, there is clearly an elephant in the room: we are missing evidence of the existence of extraterrestrial life and its nature.…”

“…A wide variety of scenarios for the origin of life have been proposed. They range from submarine hydrothermal systems and sediments, through floating pumice rafts, beach or volcanic splash pool environments, nuclear geysers, to subaerial springs (see reviews in Dass et al 2016;Westall et al 2018). Hydrothermal systems were first suggested as a suitable location for the origin of life at the surface by Harvey (1924) and at the ocean floor by Corliss et al (1981) and Baross and Hoffman (1985).…”

“…Recast from Branscomb and Russell (2018) with permission from John Wiley & Sons Ltd importance of mineral surfaces in and around hydrothermal systems (including hydrothermal sediments, cf. Westall et al 2018) for condensing organic molecules, as well as having an effect on their conformation and complexification (Hazen et al 2001;Hazen and Sverjensky 2010;Dass et al 2016. The minerals making up the edifices and the volcanic sediments surrounding them, including olivine, pyroxenes, plagioclase feldspars, oxides, oxyhydroxides, sulfides, and amorphous volcanic glass, as well as their alteration products, namely clay minerals, sulfides, oxides, carbonates and zeolite, contained transition metals which would not only have served to enhance chirality, stabilized molecules, acted as catalysts for the chemical reactions, but some, e.g., green rust and mackinawite, could also have acted as free-energy transducers and electro-conformational coupling machines (Tsong and Astumian 1988;Hazen and Sverjensky 2010;Russell 2018).…”

“…The minerals making up the edifices and the volcanic sediments surrounding them, including olivine, pyroxenes, plagioclase feldspars, oxides, oxyhydroxides, sulfides, and amorphous volcanic glass, as well as their alteration products, namely clay minerals, sulfides, oxides, carbonates and zeolite, contained transition metals which would not only have served to enhance chirality, stabilized molecules, acted as catalysts for the chemical reactions, but some, e.g., green rust and mackinawite, could also have acted as free-energy transducers and electro-conformational coupling machines (Tsong and Astumian 1988;Hazen and Sverjensky 2010;Russell 2018). Since concentration or 'crowding' of organic molecules is an important aspect of prebiotic chemistry, molecules disseminated or dissolved in fluids could also be concentrated by the mineral surfaces (Dass et al 2016Westall et al 2018). Other advantages of hydrothermal systems (sensu largo) include pH, temperature, and ionic concentrations gradients that could harness proton and redox gradients to produce chemiosmotic energy, a free-energy source that could eventually be used by the earliest biochemical systems (Russell andHall 1997, 2009;Westall et al 2018).…”

“…Whether or not this was really the case (indeed, cells could have emerged in a number of environments around the globe), it is possible that various prebiotic molecules could have been formed in a variety of environments, ranging from subaerial springs (Damer and Deamer 2015), to coastal volcanic splash pools (Fox and Strasdeit 2013), to pumice rafts (Brasier et al 2011), or submarine hydrothermal sediments. Dass et al (2016) and Westall et al (2018) reviewed the advantages and disadvantages of the various scenarios proposed for the emergence of life (as documented in Table 1) in terms of production of organic molecules, presence of complementary elements of relevance for catalyzing primitive metabolisms, availability of chemical energy for fueling reactions, availability of reactive mineral surfaces, potential for concentrating organic molecules, suitability of temperature for molecular complexification, temperature, pH and redox gradients, influence of fluid dynamics, plausibility of distribution on the Hadean Earth, and protection from impacts, radiation, etc. Of the scenarios proposed, nuclear geysers, pumice rafts, volcanic coastal splash pools, subaerial hot springs, submarine vents and hydrothermal sediments, the hydrothermal scenarios are the ones that present the most advantages, especially submarine vents and sediments.…”