UV Transmission in Natural Waters on Prebiotic Earth

Abstract

Ultraviolet (UV) light plays a key role in surficial theories of the origin of life, and numerous studies have focused on constraining the atmospheric transmission of UV radiation on early Earth. However, the UV transmission of the natural waters in which origins-of-life chemistry (prebiotic chemistry) is postulated to have occurred is poorly constrained. In this work, we combine laboratory and literature-derived absorption spectra of potential aqueous-phase prebiotic UV absorbers with literature estimates of their concentrations on early Earth to constrain the prebiotic UV environment in marine and terrestrial natural waters, and we consider the implications for prebiotic chemistry. We find that prebiotic freshwaters were largely transparent in the UV, contrary to assumptions in some models of prebiotic chemistry. Some waters, such as high-salinity waters like carbonate lakes, may be deficient in shortwave (≤220 nm) UV flux. More dramatically, ferrous waters can be strongly UV-shielded, particularly if the Fe 2+ forms highly UV-absorbent species such as . Such waters may be compelling venues for UV-averse origin-of-life scenarios but are unfavorable for some UV-dependent prebiotic chemistries. UV light can trigger photochemistry even if attenuated through photochemical transformations of the absorber ( e.g. , production from halide irradiation), which may have both constructive and destructive effects for prebiotic syntheses. Prebiotic chemistries that invoke waters that contain such absorbers must self-consistently account for the chemical effects of these transformations. The speciation and abundance of Fe 2+ in natural waters on early Earth is a major uncertainty and should be prioritized for further investigation, as it played a major role in UV transmission in prebiotic natural waters.

A Mutation Threshold for Cooperative Takeover

“…Such fluctuations translate into either higher error rates in the interaction of early replicators, higher mutation rates, or both. For example, in an analysis of UV transmission in a prebiotic setting, the conclusions of Ranjan et al are unambiguous: insofar as prebiotic chemistries are shown to be affected by UV irradiation, they must be demonstrated to either invoke a UV-shielded milieu or be so productive as to outpace UV degradation [87]. TFT's success however notably relies on being placed in an environment where interactions are reliable-that is, where no "mistakes" are made by the players.…”

Prebiotic Environments with Mg2+ and Thiophilic Metal Ions Increase the Thermal Stability of Cysteine and Non-cysteine Peptides

“…Seawater was prepared as in the study by Marcos et al with 400 mM NaCl, 20 mM MgSO 4 , 20 mM MgCl 2 , 10 mM CaCl 2 , 10 mM KCl, 2 mM NaHCO 3 , and 1.7 mM KBr at pH 8.0. The carbonate lake conditions were adapted from Toner and Catling and Ranjan et al and included 0.1 M NaH 2 PO 4 , 10 mM KBr, 1.0 M Na 2 SO 4 , 0.24 mM Na 2 SO 3 , 10 mM lithium acetoacetate, 1.0 M H 3 BO 3 , 3.0 M NaCl, 10 mM CaCO 3 , 10 mM CaCl 2 , 2.2 mM Na 2 SiO 3 , 100 mM NaHCO 3 , 7.0 mM Na 2 CO 3 , 7.0 mM NaNO 3 , 0.6 mM KI, and 0.2 mM Na 2 SO 3 at pH 9.0. The ferrous lake conditions were adapted from Ranjan et al and Hao et al and included 0.1 mM K 4 [Fe­(CN) 6 ], 0.15 mM KBr, 0.021 mM Na 2 SO 4 , 0.2 mM NaCl, 0.23 mM CaCO 3 , 0.19 mM MgCl 2 , 0.19 mM Na 2 SiO 3 , 1.0 mM NaHCO 3 , and 100 nM Na 2 CO 3 at pH 6.3.…”

“…The carbonate lake conditions were adapted from Toner and Catling and Ranjan et al and included 0.1 M NaH 2 PO 4 , 10 mM KBr, 1.0 M Na 2 SO 4 , 0.24 mM Na 2 SO 3 , 10 mM lithium acetoacetate, 1.0 M H 3 BO 3 , 3.0 M NaCl, 10 mM CaCO 3 , 10 mM CaCl 2 , 2.2 mM Na 2 SiO 3 , 100 mM NaHCO 3 , 7.0 mM Na 2 CO 3 , 7.0 mM NaNO 3 , 0.6 mM KI, and 0.2 mM Na 2 SO 3 at pH 9.0. The ferrous lake conditions were adapted from Ranjan et al and Hao et al and included 0.1 mM K 4 [Fe­(CN) 6 ], 0.15 mM KBr, 0.021 mM Na 2 SO 4 , 0.2 mM NaCl, 0.23 mM CaCO 3 , 0.19 mM MgCl 2 , 0.19 mM Na 2 SiO 3 , 1.0 mM NaHCO 3 , and 100 nM Na 2 CO 3 at pH 6.3. For the heat degradation experiments, 200 μL of 5 mM peptide solution was placed in glass vials that were preheated at 150 °C in a Corning LSE digital dry bath heater and incubated.…”

Can prebiotic reaction systems survive in the wild? An interference chemistry approach

“…However, many bystander species may attenuate the transmission of UV light in geochemically realistic complex aqueous solutions. Ranjan et al [88] found that Fe-containing species in e.g., ferrocyanide lakes are efficient at attenuating UV transmission, diminishing the potential for UV-driven constructive organic synthesis, but similarly slowing UV-driven degradation of other molecules that may go on to accumulate and constructively interact along different paths, e.g., meteoritic nucleobases [89].…”