[Effect of processes in the earth's crust on evolution of photosynthesis (as indicated by data on carbon isotopic composition)]

Abstract

A probable mechanism of effect of processes occurring in the Earth's crust on evolution of photosynthesis is considered. According to the hypothesis, this effect is realized through entrance to the Earth's atmosphere of carbon dioxide that stimulates photosynthesis. Supply of CO2 is irregular and is due to irregular movements of the Earth's crust plates. This is accompanied by destruction of carbonates and conversion of carbon of the organic matter to CO2 due to processes of reduction of sulfates. The CO2 content in atmosphere rises for relatively short orogenic periods, due to intensive crust plate movement, while for the subsequent long periods, called the geosynclinal ones, of the relatively slow plate movement, the CO2 content falls due to the higher rate of its consumption for photosynthesis. Owing to the carbon isotopic fractionation accompanying photosynthesis, regular isotopic differences appear between the atmospheric CO2 and the "living" matter (Relay's effect); these differences are then transformed to isotope differences of the carbonate and organic carbon. At the appearance in atmosphere of free oxygen--product of photosynthesis--in organisms there appears photorespiration that also is accompanied by fractionation of carbon isotopes, but with effect of opposite sign. This leads to enrichment of the photosynthesizing biomass with 13C isotope at the orogenic periods. As a result, the initially pronounced isotope differences of the carbonate and organic carbon decrease by the end of the geosyclinal periods. According to the proposed model, concentrations of CO2 and O2 are exchanged in the antiphase. They lead to alternation of periods of warning up and cooling off on the Earth. The former coincide with the orogenic periods, the latter appear at the end of geosyclinal periods when oxygen is accumulated in atmosphere, while organic substance in sediments. Accumulation of organic substance leads to formation of petroleum-maternal masses. To substantiate the model, data on isotope composition of carbon of carbonate and organic substance in rocks are used and its ability to explain several known natural regularities and empirical correlations. The model is used for analysis of some key stages of evolution of photosynthesis.