text: A suggestion has been made that in the early stages of the Earths development when its radioactivity was almost two orders of magnitude higher than at present, radiolysis could have been the principal source of atmospheric oxygen, which ensured the conditions for the origin and development of life. Molecular hydrogen and oxidants produced by the radiolysis of water may also provide a continuous source of energy to subsurface microbial communities (Pedersen, 1999). Such speculation is supported by a discovery in the Mponeng Gold Mine in South Africa, where the researchers found a community dominated by a new phylotype of Desulfotomaculum', feeding on primarily radiolytically produced H.