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On the surface of the early Earth and Earth-like exoplanets ultraviolet (UV) light acts as an important energy source. Particularly, UV light of different wavelength ranges can trigger a variety of photochemical reactions relevant to the molecular origins of life. However, the penetration depth of UV light into natural waters on early Earth and Earth-like exoplanets has remained an open question in the past decades. We therefore studied the absorption of various salt constituents of prebiotic lakes in aqueous solution in the range between 200 nm and 360 nm.[1] We found penetration depths from a few 100 µm to several 10 m depending on the lake scenarios. The deep UVC wavelengths around 200 nm are blocked more rapidly than longer wavelength irradiation up to 300 nm, resulting in depth-dependent irradiation spectra. The photochemical reactions initiated by this UV irradiation can not only interrupt chemical reaction networks, but instead they can also repair damage. An example for a productive UV-induced process is the self-repair of photolesions in short DNA oligonucleotides.[2] Ultrafast UV pump, mid-infrared (MIR) probe spectroscopy in the range of picoseconds to nanoseconds allowed us to monitor the light-induced processes in real time and revealed that the repair is initiated by a transient charge separation in a photolyase-like mechanism.[3] The self-repair via charge transfer is highly sequence dependent and may have influenced sequence selection in the prebiotic era.
[1] S. Ranjan, C. L. Kufner, G. G. Lozano, Z. R. Todd, A. Haseki, D. D. Sasselov, Astrobiology 2021, Accepted Manuscript.
[2] D. B. Bucher, C. L. Kufner, A. Schlueter, T. Carell, W. Zinth, J. Am. Chem. Soc. 2016, 138, 186–190.
[3] C. L. Kufner, W. Zinth, D. B. Bucher, ChemBioChem 2020, 21, 1-6.
