炭素の地球化学的サイクルと大気・海洋の起源(<特集>地球における炭素の循環)

概要

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The most important question to the Earth's environment is when and how atmosphere and oceans were formed on the primordial Earth. A geological approach to solve the question is to examine the distribution of carbonate rocks and sedimentary organic matter in geological sequences. Sedimentary carbon in carbonates and organic matter was produced from CO_2 in the atmosphere-ocean system through the geochemical cycle. The total sedimentary carbon in the Phanerozoic amounts to 61-36×10^<21>g which correspond to 28-5 atm of CO_2 in the Earth's atmosphere. This tremendous amount of CO_2 can not be considered to be present in the atmosphere-ocean system before the Phanerozoic, because if that amount of CO_2 had been present, the greenhouse effect should have kept the Earth's surface at high temperature like the present Venus. This is in contradiction with geological evidences. It is concluded that CO_2 together with volatile matter including H_20 was degassed in the Phanerozoic time to evolve the atmosphere and oceans on the Earth. The catastrophic early degassing hypothesis is not acceptable from the geological examination of the sedimentary carbon.
地学団体研究会の論文
1994-07-25