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UV surface radiance for early Earth as a function of ΦS, using the models of Hu et al. (2013). The black solid line indicates the top-of-atmosphere (TOA) flux, i.e., the irradiation incident at the top of the atmosphere from the young Sun. The vertical dashed line demarcates 254 nm, the wavelength at which the low-pressure mercury lamps commonly used in prebiotic chemistry experiments emit.
