UV radiation from the young Sun and oxygen and ozone levels in the prebiological palaeoatmosphere

Abstract

UV measurements of young T-Tauri stars, resembling the Sun at an age of a few million years, have recently been made with the International Ultraviolet Explorer. They indicate that young stars emit up to 10⁴ times more UV than the present Sun. The implications for the origin and evolution of O₂ and O₃ in the prebiological palaeoatmosphere are presented here. The results of photochemical calculations indicate that the O₂ surface mixing ratio was a factor 10⁴-10⁶ times greater than the standard value of 10^-15. This new value reconciles the simultaneous existence of oxidized iron and reduced uranium.