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Introduction

A qualitative geosphere-biosphere model consisting of the components solid Earth, hydrosphere, atmosphere, and biosphere is considered. The model is based on a quasi-equilibrium of the large-scale global carbon balance between the main sources and sinks modified by the biosphere. To calculate the weathering rate we take into account the growth of continental area over geological time scales and extrapolate the present continental growth rate to the future. We determine the ``life corridor'' for the existence of a photosynthesis-based biosphere dependent on the state parameters of the Earth system. Furthermore, the habitable zone around the Sun in the past, present and the planetary future under certain boundary conditions of the existence of photosynthesis-based life is calculated.



W. von Bloh
Thu Aug 26 10:56:00 NFT 1999