Is formamide a geochemically plausible prebiotic solvent?

Abstract

From a geochemical perspective, significant amounts of pure formamide (HCONH2) would have likely been rare on the early Earth. There may have been mixed formamide-water solutions, but even in the presence of catalyst, solutions with >20 weight% water in formamide would not have produced significant amounts of prebiotic compounds. It might be feasible to produce relatively pure formamide by a rare occurrence of freezing formamide/water mixtures at temperatures lower than formamide's freezing point (2.55 °C) but greater than the freezing point of water. Because of the high density of formamide ice it would have sunk and accumulated at the bottom of the solution. If the remaining water froze on the surface of this ice, and was then removed by a sublimation-ablation process, a small amount of pure formamide ice might have been produced. In addition a recent report suggested that ∼85 weight% formamide could be prepared by a geochemical type of fractional distillation process, offering another possible route for prebiotic formamide production.

The key role of meteorites in the formation of relevant prebiotic molecules in a formamide/water environment

“…Unlike recent theoretical argumentation of the contrary40, the data described here and in ref. 33 show that NH 2 CHO/water is a flexible and fertile prebiotic incubator.…”

A Stark Contrast to Modern Earth: Phosphate Mineral Transformation and Nucleoside Phosphorylation in an Iron‐ and Cyanide‐Rich Early Earth Scenario

“…Theprebiotic hydrosphere was also significantly different from that of the modern Earth, free of abundant oxygen and enriched in reduced chemical species.S mall lakes and ponds of water were likely enriched in urea, formed through multiple prebiotic reactions, [37][38][39] along with formamide and ammonium formate,resulting from the hydrolysis of cyanide and cyanamide. [40,41] These small bodies of water,t hrough repeated heating and evaporation, could become enriched in these dissolved organics,w hich would oscillate in compositions and concentrations depending on changing levels of water activity.A ts ome points this could create av iscous, multicomponent solvent during times of particularly low water activity. [8,22] Thus,the components of this pond would be expected to exist in ad ynamic equilibrium upon repeated drying and rewetting with their ratios depending, at any point in time,o nt he temperature,w ater activity,a nd the recent history of the pond.…”

“…Thef ormation of this low-water-activity solvent would inhibit further loss of some volatile components,i ncluding ammonium, formate,a nd formamide,b ut might protect some molecules that are labile in high-wateractivity mediums. [8,22,41] Thei nteraction between this ureaand organic-enriched prebiotic milieu and the minerals from the local geosphere were likely akey step in the formation of secondary minerals that have proven to be more favorable for organic molecule phosphorylation. [8] When allowed to evolve anaerobically at ambient temperature and in the presence of indirect sunlight, this amorphous iron phosphate mineral phase was observed to crystallize into the mixed-iron-valence phosphate phase beraunite [(Fe 2+ Fe 3+ ) 5 (OH) 5 (PO 4 ) 4 ·4 H 2 O; Figure S6 c, d].T he formation of beraunite and vivianite demonstrates that it is possible to create mixed-valence-iron minerals on ap rebiotic Earth (without oxygen) through sunlight-driven oxidation in aSchikkorr-like reaction, producing H 2 and OH À from waters of crystallization.…”

The Prebiotic Provenance of Semi-Aqueous Solvents

“…In 1976, Schoffstall published work using formamide as a nonaqueous medium, where mild heat (70°C) resulted in the phosphorylation of adenosine to form ADP, AMP, and cyclic AMP (Schoffstall 1976). A large reservoir of pure, neat formamide on the prebiotic Earth was unlikely (Bada et al 2016) but may have been available in microenvironments such as evaporating tidal pools (Adam et al 2018;Vichietti et al 2019), or as a solute. Accordingly, semi-aqueous solvents with low water activities have also been explored with respect to the origin of life such as the urea-ammonium formate mixtures of Burcar et al 2016.…”