A general modelling scheme for assessing the suitability for life on any Earth-like extrasolar planet is presented. This approach is based on an integrated Earth system analysis in order to calculate the habitable zone in main-sequence-star planetary systems. The habitability is investigated following a concept, which assumes the long-term possibility of photosynthetic biomass production under geodynamic conditions. Consequently, a broad variety of climatological, biogeochemical, and geodynamical processes involved in the generation of photosynthesis-driven life conditions are taken into account. Within this model the evolution of the habitable zone over geological time scales can be calculated straightforwardly and allows an estimate of the probability that an Earth-like planet is within the habitable zone around an extrasolar planetary system. In particular, the stellar luminosity and the age of star/planet system are of fundamental importance for planetary habitability.