Prebiotic synthesis from CO atmospheres: Implications for the origins of life

Abstract

Most models of the primitive atmosphere around the time life originated suggest that the atmosphere was dominated by carbon dioxide, largely based on the notion that the atmosphere was derived via volcanic outgassing, and that those gases were similar to those found in modern volcanic effluent. These models tend to downplay the possibility of a strongly reducing atmosphere, which had been thought to be important for prebiotic synthesis and thus the origin of life. However, there is no definitive geologic evidence for the oxidation state of the early atmosphere and bioorganic compounds are not efficiently synthesized from CO 2 atmospheres. In the present study, it was shown that a CO-CO 2-N2-H2O atmosphere can give a variety of bioorganic compounds with yields comparable to those obtained from a strongly reducing atmosphere. Atmospheres containing carbon monoxide might therefore have been conducive to prebiotic synthesis and perhaps the origin of life. CO-dominant atmospheres could have existed if the production rate of CO from impacts of extraterrestrial materials were high or if the upper mantle had been more reduced than today.

An unconventional pathway for reduction of CO 2 to methane in CO-grown Methanosarcina acetivorans revealed by proteomics

“…The microbial metabolism of CO is an important component of the global carbon cycle (1,2), and CO is believed to have been present in the atmosphere of early Earth that fueled the evolution of primitive metabolisms (3)(4)(5)(6)(7). Investigations of aerobic species from the Bacteria domain have contributed important insights into microbial CO oxidation (8,9), as have investigations of anaerobes from the Bacteria domain that conserve energy by coupling CO oxidation to H 2 evolution (10)(11)(12).…”

Astrobiology and the Possibility of Life on Earth and Elsewhere…

“…Since Miller's initial publication, many laboratories have replicated and extended his results, exploring variations on the synthesis using other types of apparatus designs, gas mixtures and energy sources (Groth and Weyssenhoff 1957;Menor-Salvan et al 2009;Miller 1957aMiller , 1957bMiyakawa et al 2002aMiyakawa et al , 2002bMiyakawa et al , 2002cParker et al 2010Parker et al , 2011Ring et al 1972;Miller 1983a, 1983b), demonstrating the synthesis of a much wider variety of organic compounds. There is a consensus of the types of products obtained using similar gases, though there are important differences in the C and energy yields of various intermediate species such as HCHO and HCN (Miller and Schlesinger 1984) depending on the energy source and gas mixture used (Heinrich et al 2007), factors independent of surface conditions.…”

“…At low fluxes, compounds such as HCN may hydrolyze to less complex species faster than they undergo reactions that produce biologically interesting molecules (Miyakawa et al 2002a(Miyakawa et al , 2002b(Miyakawa et al , 2002c, with the specific rates depending on aqueous temperature and pH conditions. Thus, terrestrial surface conditions may also have been important factors when considering the efficiency of atmospherically-mediated organic synthesis on the primitive Earth.…”

“…Alternative chemical pathways toward the formation of amino acids in photolyzed ice mixtures have also been recently proposed (Bossa et al 2010) with circularly polarized light initiating an enantiomeric excess of amino acids (Modica et al 2014). Various nucleobases synthesis pathways have been established since the 1960s (see for instance : Ferris and Orgel 1966;Menor-Salván and Marín-Yaseli 2013;Miyakawa et al 2002aMiyakawa et al , 2002bMiyakawa et al , 2002cOro 1960;Oro and Kimball 1961;Robertson and Miller 1995) (see also Martins 2012 for a review). It has also been shown that a component of the organic residue synthesized by irradiation of interstellar and cometary ice spontaneously organizes into boundary structures .…”

Conducting Miller-Urey Experiments

“…For example, more oxidized gas mixtures can be used 14,18,19 . Furthermore, using modifications of the apparatus, the energy source can be changed, for example, by using a silent discharge 4 , ultraviolet light 20 , simulating volcanic systems 4,12,21 , imitating radioactivity from Earth's crust 22 , and mimicking energy produced by shockwaves from meteoritic impacts 23 , and also cosmic radiation 18,19 .…”