Estimating the capacity for production of formamide by radioactive minerals on the prebiotic Earth

Abstract

Water creates special problems for prebiotic chemistry, as it is thermodynamically favorable for amide and phosphodiester bonds to hydrolyze. The availability of alternative solvents with more favorable properties for the formation of prebiotic molecules on the early Earth may have helped bypass this so-called “water paradox”. Formamide (FA) is one such solvent, and can serve as a nucleobase precursor, but it is difficult to envision how FA could have been generated in large quantities or accumulated in terrestrial surface environments. We report here the conversion of aqueous acetonitrile (ACN) via hydrogen cyanide (HCN) as an intermediate into FA by γ-irradiation under conditions mimicking exposure to radioactive minerals. We estimate that a radioactive placer deposit could produce 0.1‒0.8 mol FA km−2 year−1. A uraninite fission zone comparable to the Oklo reactors in Gabon can produce 0.1‒1 mol m−2 year−1, orders of magnitude greater than other scenarios of FA production or delivery for which reaching sizeable concentrations of FA are problematic. Radioactive mineral deposits may be favorable settings for prebiotic compound formation through emergent geologic processes and FA-mediated organic chemistry.

Radiolytic Synthesis of Cyanogen Chloride, Cyanamide and Simple Sugar Precursors

“…In contrast to the uranium deposits formed by oxygen‐driven precipitation like those found at Oklo, Hadean radioactive seams would have been formed via hydrodynamic sorting of uranium‐rich source rocks, such as uraninite, without need of intermediate precipitation steps ,. Regardless of the formation process, a fission zone comparable in size to those found at Oklo in Gabon has the ability to foster, a localized but highly radioactive environment for about 500,000 years. Others have proposed that higher output of solar energetic particles from the young Sun via more frequent solar flares and coronal mass ejections would have exposed the atmosphere of the early Earth to significantly higher fluxes of radiation in comparison to today .…”

“…There has been speculation that radiolytic chemistry may have played, a direct role in the complex chemical networks thought necessary for the origins of life on Earth. Ancient radioactive mineral deposits such as those containing monazite and uraninite could have provided, locally high fluxes of alpha, beta and gamma radiation on their surfaces.…”

“…There has been speculation that radiolytic chemistry may have played, a direct role in the complex chemical networks thought necessary for the origins of life on Earth. Ancient radioactive mineral deposits such as those containing monazite and uraninite could have provided, locally high fluxes of alpha, beta and gamma radiation on their surfaces. Organic accretion layers accumulated on the surfaces of radioactive mineral grains that have been found in the geological record serve as evidence that organic radiolysis reactions can occur in nature in microenvironments found in close proximity to radioactive mineral grain surfaces.…”

“…Over a dozen individual fission zones are known from the Oklo locality in Gabon ,. In contrast to the uranium deposits formed by oxygen‐driven precipitation like those found at Oklo, Hadean radioactive seams would have been formed via hydrodynamic sorting of uranium‐rich source rocks, such as uraninite, without need of intermediate precipitation steps ,. Regardless of the formation process, a fission zone comparable in size to those found at Oklo in Gabon has the ability to foster, a localized but highly radioactive environment for about 500,000 years.…”

HNCO-based synthesis of formamide in planetary atmospheres

“…Formamide-based chemistry is a broadly discussed scenario relating to the origin of biomolecules (Saladino et al 2004(Saladino et al , 2012bFerus et al 2011bFerus et al , 2012Ferus et al , 2014Ferus et al , 2017bSaitta & Saija 2014;Pino et al 2015;Šponer et al 2016a,b;Adam et al 2018;Becker et al 2018;Benner et al 2012). Besides the traditional HCNand reducing-atmospheres based biomolecules synthesis (Ferris et al 1974;Yuasa et al 1984;Levy et al 1999;Sutherland 2016;Civiš et al 2017), the current evidence shows that the formamide molecule did not necessary play role of merely starting parent prebiotic precursor, but also it could serve as an intermediate compound in prebiotic synthesis (Ferus et al 2017b).…”