Understanding the origin of life on Earth is key to understanding how it might start elsewhere. Recent laboratory studies (e.g., Patel et al. 2015) suggest UV light may have played a critical role in the synthesis of molecules relevant to the origin of life (prebiotic chemistry), such as RNA. We show that UV light interacts with prebiotic chemistry in ways that may be sensitive to the spectral shape and overall amplitude of irradiation (e.g., Ranjan & Sasselov 2016a). We use radiative transfer models to constrain the UV environment on early Earth (3.9 Ga). We find that the surface UV is insensitive to much of the considerable uncertainty in the atmospheric state, enabling us to constrain the UV environment for prebiotic chemistry on early Earth (Ranjan & Sasselov 2016b). Some authors (e.g., Benner et al. 2015) have suggested Mars as a venue for prebiotic chemistry. Therefore, we explore plausible UV spectral fluences on Mars at 3.9 Ga, and compare early Mars and Earth as venues for UV-sensitive prebiotic chemistry. Finally, we calculate the UV fluence on planets orbiting M-dwarfs, and compare them to early Earth as venues for prebiotic chemistry and the origin of life.