Long-term stability of climate and global glaciations throughout the evolution of the Earth
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2007
Received: 7 November 2005
Accepted: 8 December 2006
Published: 7 May 2007
Earth’s climate is considered to be stable on the order of > 106 years, owing to a negative feedback mechanism in a carbon cycle system. However, any decrease in net input flux of CO2 to the atmosphere-ocean system (i.e., volcanic-metamorphic CO2 flux minus excess organic carbon burial flux) lowers the surface temperature and would eventually initiate global glaciation. The F D -F O B diagram (F D : the total CO2 degassing flux, F O B : the organic carbon burial flux) is proposed as a measure of the susceptibility of the Earth to global glaciations. By using this diagram with the carbon fluxes estimated from a carbon cycle model during the Phanerozoic, the net input flux of CO2 is found to have been very close to the critical condition for a global glaciation at the Late Paleozoic. During the Proterozoic, a carbon isotope mass balance model with this diagram shows that global glaciations occurred probably due to a decrease in the CO2 degassing in addition to an increase in the organic carbon burial. Because the Sun becomes brighter as it evolves, the critical level of atmospheric CO2 pressure to cause global glaciation will be lower than the critical CO2 pressure for photosynthesis of C4 plants within 500 million years. At this point, the net input flux of CO2 will be too large to cause global glaciations. Continuous volcanic-metamorphic activities (i.e., plate tectonics) may be one of the necessary conditions for the Earth and Earth-like planets in extrasolar planetary systems to keep liquid water and life over the timescales of planetary evolution.