  The emergence of life on Earth is a highly discussed but still unsolved
question. Current research underlines the importance of environments within
close proximity to the Earth's surface as they can solve long-standing problems
such as polymerization of nucleotides and phosphorylation of nucleosides.
However, near-surface settings, for example, ponds or ice shields, are prone to
UV irradiation. We investigated the photosensitivity of uracil, uridine,
adenosine, cytidine, and guanosine by using Raman microscopy. The samples were
irradiated by a UV source with 150~mW/cm\textsuperscript{2} for 10 min. Uracil
and uridine showed the highest photosensitivity, while adenosine, cytidine, and
guanosine remained stable. The change of spectral features and ab initio
quantum calculations indicate the formation of uracil's trans-syn cyclobutane
dimer during UV irradiation.
