Influence of the UV Environment on the Synthesis of Prebiotic Molecules

Abstract

Ultraviolet radiation is common to most planetary environments and could play a key role in the chemistry of molecules relevant to abiogenesis (prebiotic chemistry). In this work, we explore the impact of UV light on prebiotic chemistry that might occur in liquid water on the surface of a planet with an atmosphere. We consider effects including atmospheric absorption, attenuation by water, and stellar variability to constrain the UV input as a function of wavelength. We conclude that the UV environment would be characterized by broadband input, and wavelengths below 204 nm and 168 nm would be shielded out by atmospheric CO2 and water, respectively. We compare this broadband prebiotic UV input to the narrowband UV sources (e.g., mercury lamps) often used in laboratory studies of prebiotic chemistry and explore the implications for the conclusions drawn from these experiments. We consider as case studies the ribonucleotide synthesis pathway of Powner et al. (2009) and the sugar synthesis pathway of Ritson and Sutherland (2012). Irradiation by narrowband UV light from a mercury lamp formed an integral component of these studies; we quantitatively explore the impact of more realistic UV input on the conclusions that can be drawn from these experiments. Finally, we explore the constraints solar UV input places on the buildup of prebiotically important feedstock gasses like CH4 and HCN. Our results demonstrate the importance of characterizing the wavelength dependence (action spectra) of prebiotic synthesis pathways to determine how pathways derived under laboratory irradiation conditions will function under planetary prebiotic conditions.

The Surface UV Environment on Planets Orbiting M Dwarfs: Implications for Prebiotic Chemistry and the Need for Experimental Follow-up

“…This scenario is consistent with our understanding of conditions on prebiotic Earth: UV light is thought to have been abundant on young Earth as a result ofthe absence of a biogenic ozone layer (Cockell 2000a(Cockell , 2000bRanjan & Sasselov 2016). Prebiotic photochemistry interacts with UV radiation in ways that are sensitive to its spectral shape and overall intensity (Ranjan & Sasselov 2016). Consequently, it is important to constrain the UV environment on the surface of planets orbiting Mdwarfsto understand if UV-sensitive prebiotic chemistry pathways that could have lead to the origin of life on Earth could function on such worlds.…”

“…Measurements of nucleobase photostability suggest that the biogenic nucleobases (the informational components of the RNA and DNA monomers) are exceptionally stable to UV irradiation compared to structurally similar molecules with comparable thermal properties, suggesting thatthey evolved in a UV-rich environment (Rios & Tor 2013;Beckstead et al 2016;Pollum et al 2016). This scenario is consistent with our understanding of conditions on prebiotic Earth: UV light is thought to have been abundant on young Earth as a result ofthe absence of a biogenic ozone layer (Cockell 2000a(Cockell , 2000bRanjan & Sasselov 2016). Prebiotic photochemistry interacts with UV radiation in ways that are sensitive to its spectral shape and overall intensity (Ranjan & Sasselov 2016).…”

UV surface habitability of the TRAPPIST-1 system

“…in an ocean or under soil (see e.g. Ranjan & Sasselov 2016), but this would make it harder to detect life remotely. However, some biological UV-protection methods, such as biofluorescence, could make such a biosphere in high surface UV environments detectable (O'Malley-James & Kaltenegger 2016).…”

Inventive processes in nature: from information origin in chemical evolution to technological exhaustion

“…This uncertainty represents the missing information prior to the experiment. After the UV pulse irradiates the planet, the remaining photochemically synthesised metastable molecules (Ranjan and Sasselov 2016) remove this uncertainty by holding experimental outcome information. These newly synthesised, metastable molecules decay unevenly, depending on the molecular structure and local environmental conditions.…”