What it is
Many heterocyclic molecules resembling the canonical nucleobases of DNA and RNA could have existed on the early Earth, yet extant biology generally uses the canonical set, and ultraviolet light, likely abundant at the early Earth's surface, has been suggested to play a role in selecting it. The authors measured how fast various canonical and noncanonical nucleobases and nucleosides degrade under continuous UV irradiation, and estimated their relative photostability under a plausible early-Earth UV environment. The canonical nucleobases and nucleosides spanned nearly the entire range of observed photodegradation rates.
Why it matters
Earlier photophysics studies suggested that the canonical molecules have shorter excited-state lifetimes and may therefore be less prone to photodamage. Measured directly under continuous irradiation, photostability did not single them out, and the authors conclude that the factors selecting the genetic alphabet may be more complex than UV photostability alone.
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Filed underOrigins and Evolution of Life, Paleontology and Stratigraphy of Fossils, Space Science and Extraterrestrial Life