Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly
energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological
mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from
oxygen produced by photosynthesis) accumulated in the stratosphere. In an effort to better understand the UV liability of
DNA, we used synchrotron light to measure VUV-UV absorption spectra (125-340 nm) for DNA and its components
(oligonucleotides and mononucleotides). We also measured VUV-UV absorption spectra for potential and known UV
screens, including amino acids, proteins, amines (including polyamines), scytonemin, mycosporine-like amino acids, β-
carotene, melanin and flavonoids. Among these, flavonoids seem remarkably suited to protecting DNA in the VUV-UV.
Flavonoids accumulate in seed coats, where they confer resistance to monochromatic UV (254 nm) and polychromatic
UV (200-400 nm). We discuss these findings in relation to the origin and evolution of life and its potential dispersal
through space.
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