連続脱ガスと地球環境の安定性 : 地球化学的炭素循環モデルからの制約

抄録

The rate of CO₂ degassing to the atmosphere-ocean system via volcanism has probably changed greatly during the history of the Earth. Change of the CO₂ degassing rate results in change of the atmospheric CO₂ level and so the climate, through the geochemical cycle of carbon at the surface of the Earth. If the CO₂ degassing may cease or weaken suddenly, a carbon geochemical cycle model coupled with ocean chemistry and the climate model predicts that the Earth's surface environment should cool very rapidly on the order of 10⁵ yr, and, at last, fall into the globally ice covered state. The time required for this is estimated to be on the order of 10⁶ years throughout the Earth's history, irrespective of large change of the atmospheric CO₂ level with time. However, absence of geological evidence for such an exstreme climate in the past suggests that the CO₂ degassing process via volcanism should have been almost contiuous, at least, on the order of >10⁵-10⁶ yr, which indicates continuity of plate tectonics on the Earth.