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This book is a synthesis of a series of outstanding research articles by Professor Budyko on climatology and by Professor Ronov on geochemistry and an expansion of their previous collaborative work on the evolution of atmospheric composition. Although other topics are briefly mentioned, the book is mainly devoted to the calculation of the levels of atmospheric CO2 and O2 over Phanerozoic time. Their basic assumption is that the worldwide abundance of carbonate minerals and organic matter in sedimentary rocks as a function of age, based on the exhaustive collection of data by A. B. Ronov and coworkers, can be used to calculate atmospheric composition. The reasoning is quite simple. It is assumed that CO2 given off to the atmosphere by volcanic and metamorphic degassing is removed mainly in the form of carbonate minerals in sediments (organic matter being much less abundant). The total mass of carbonate for each age period, divided by the length of the period, gives the rate at which CO2 is removed from the atmosphere via burial in sediments. Since so little CO2 is in the atmosphere, compared to fluxes to and from it on a geological time scale, rates of removal must equal rates of addition and so carbonate burial rates also give rates of addition to the atmosphere via volcanism. Since removal rates are also assumed to be directly proportional to the mass of CO2 present in the atmosphere (linear feedback), by determining the proportionality constant, one can directly calculate CO2 levels from rock abundances. For atmospheric O2 , production rates are calculated from the burial rates for organic carbon, and removal rates (via the oxidation of sulfides, ferrous minerals, and volcanic gases) are again assumed to be directly proportional to the mass of O2 in the atmosphere which, on equating production and removal rates, enables calculation of O2 levels over Phanerozoic time.