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Timescales for Prebiotic Photochemistry Under Realistic Surface Ultraviolet Conditions.

Authors
  • Rimmer, Paul B1, 2, 3
  • Thompson, Samantha J2
  • Xu, Jianfeng3
  • Russell, David A3
  • Green, Nicholas J3
  • Ritson, Dougal J3
  • Sutherland, John D3
  • Queloz, Didier P2
  • 1 Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom. , (United Kingdom)
  • 2 Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom. , (United Kingdom)
  • 3 MRC Laboratory of Molecular Biology, Cambridge, United Kingdom. , (United Kingdom)
Type
Published Article
Journal
Astrobiology
Publisher
Mary Ann Liebert
Publication Date
Sep 01, 2021
Volume
21
Issue
9
Pages
1099–1120
Identifiers
DOI: 10.1089/ast.2020.2335
PMID: 34152196
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Ultraviolet (UV) light has long been invoked as a source of energy for prebiotic chemical synthesis, but experimental support does not involve sources of UV light that look like the young Sun. Here we experimentally investigate whether the UV flux available on the surface of early Earth, given a favorable atmosphere, can facilitate a variety of prebiotic chemical syntheses. We construct a solar simulator for the UV light of the faint young Sun on the surface of early Earth, called StarLab. We then attempt a series of reactions testing different aspects of a prebiotic chemical scenario involving hydrogen cyanide (HCN), sulfites, and sulfides under the UV light of StarLab, including hypophosphite oxidation by UV light and hydrogen sulfide, photoreduction of HCN with bisulfite, the photoanomerization of α-thiocytidine, the production of a chemical precursor of a potentially prebiotic activating agent (nitroprusside), the photoreduction of thioanhydrouridine and thioanhydroadenosine, and the oxidation of ethanol (EtOH) by photochemically generated hydroxyl radicals. We compare the output of StarLab to the light of the faint young Sun to constrain the timescales over which these reactions would occur on the surface of early Earth. We predict that hypophosphite oxidation, HCN reduction, and photoproduction of nitroprusside would all operate on the surface of early Earth in a matter of days to weeks. The photoanomerization of α-thiocytidine would take months to complete, and the production of oxidation products from hydroxyl radicals would take years. The photoreduction of thioanhydrouridine with hydrogen sulfide did not succeed even after a long period of irradiation, providing a lower limit on the timescale of several years. The photoreduction of thioanhydroadenosine with bisulfite produced 2'-deoxyriboadenosine (dA) on the timescale of days. This suggests the plausibility of the photoproduction of purine deoxyribonucleotides, such as the photoproduction of simple sugars, proceeds more efficiently in the presence of bisulfite.

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