Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom.
Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom.
Astrobiology. 2021 Sep;21(9):1099-1120. doi: 10.1089/ast.2020.2335. Epub 2021 Jun 21.
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.
紫外线 (UV) 长期以来一直被认为是原始化学合成的能源来源，但实验支持并不涉及看起来像年轻太阳的 UV 光源。在这里，我们通过实验研究了在有利的大气条件下，早期地球上可用的 UV 通量是否能够促进各种原始化学合成。我们构建了一个称为 StarLab 的早期地球表面微弱年轻太阳 UV 光的太阳模拟器。然后，我们在 StarLab 的 UV 光下尝试了一系列反应，以测试涉及氢氰酸 (HCN)、亚硫酸盐和硫化物的原始化学场景的不同方面，包括 UV 光下的次膦酸盐氧化和硫化氢、亚硫酸氢盐与 HCN 的光还原、α-硫胞苷的光互变异构、潜在原始激活剂（硝普盐）的化学前体的生成、硫代尿嘧啶和硫代腺苷的光还原以及通过光化学产生的羟基自由基氧化乙醇 (EtOH)。我们将 StarLab 的输出与微弱年轻太阳的光进行比较，以限制这些反应在早期地球表面发生的时间尺度。我们预测，次膦酸盐氧化、HCN 还原和硝普盐的光生成都将在早期地球上数天到数周内发生。α-硫胞苷的光互变异构需要数月才能完成，而羟基自由基的氧化产物的生成则需要数年。即使经过长时间的辐照，硫代尿嘧啶与硫化氢的光还原也没有成功，这为几年的时间尺度提供了下限。亚硫酸氢盐与 HCN 的光还原在数天的时间尺度上产生了 2'-脱氧腺苷 (dA)。这表明在亚硫酸氢盐存在的情况下，嘌呤脱氧核苷酸的光生成，例如简单糖的光生成，更有效。
