Surface radiances on early Earth-like planets orbiting different M dwarfs including HIP 23309, computed as in Ranjan et al. (2017). The Rimmer et al. (2018) minimum flux criterion for HCN homologation toward ribonucleotide synthesis is shown in pink. Extremely active stars like HIP 23309 meet the Rimmer et al. (2018) criterion, illustrating the need to constrain UV emission of M dwarfs over the course of their lifetimes to understand the potential of life search on M-dwarf planets to test theories of abiogenesis (Rimmer et al. 2021a).