A THEORETICAL APPROACH TO P_(co_2) EVOLUTION IN THE ATMOSPHERE BASED ON ASSOCIATIONS OF SEDIMENTARY MINERALS

Based on the theory of pH evolution of sea water and the balance between the seawater and the atmosphere the authors discussed the problems about (i) the method ofcalculating P_(CO_2) in the ancient atmosphere with the associations of sedimentary miner-als; (ii) the evolution of P_(CO_2) values in the geologic history; (iii) the relations of thepH evolution of sea water with carbonate precipitations; and (iv) calculation of the pHlimit for some associations of sedimentary minerals and its corresponding P_(CO_2) valuesin the atmosphere. The authors pointed out that though carbonates had deposited little in the Archaean,the content of CO_2 gas in the Archaean atmosphere was very high and was gradually go-ing up to form a thick CO_2 atmosphere. Up to 2600 Ma ago, the P_(CO_2) had reached a gradeof 10- 50 atm. There was a general trend of evolution that from the early Proterozoicera to the present the depositional horizon of carbonate layers was gradually risingand finally surpassed the horizons of clay min

A THEORETICAL APPROACH TO P_(co_2) EVOLUTION IN THE ATMOSPHERE BASED ON ASSOCIATIONS OF SEDIMENTARY MINERALS

Based on the theory of pH evolution of sea water and the balance between the sea water and the atmosphere the authors discussed the problems about (i) the method of calculating P_(CO_2) in the ancient atmosphere with the associations of sedimentary miner- als; (ii) the evolution of P_(CO_2) values in the geologic history; (iii) the relations of the pH evolution of sea water with carbonate precipitations; and (iv) calculation of the pH limit for some associations of sedimentary minerals and its corresponding P_(CO_2) values in the atmosphere. The authors pointed out that though carbonates had deposited little in the Archaean, the content of CO_2 gas in the Archaean atmosphere was very high and was gradually go- ing up to form a thick CO_2 atmosphere. Up to 2600 Ma ago, the P_(CO_2) had reached a grade of 10- 50 atm. There was a general trend of evolution that from the early Proterozoic era to the present the depositional horizon of carbonate layers was gradually rising and finally surpassed the horizons of clay minerals and sulfides. The corresponding P_(CO_2) in the atmosphere was lowering from the thick CO_2 atmosphere to the present 0.03% atm. On the basis of the calculated P_(CO_2) sizes and its fluctuation characteristics the history of P_(CO_2) evolution can be divided into three major stages.