Role of low solar luminosity in the history of the biosphere |
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| Authors: | E M Galimov |
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| Institution: | 1.Vernadsky Institute of Geochemistry and Analytical Chemistry,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth’s surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO2, CH4, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO2 content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO2 as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO2, the uptake of atmospheric CO2 related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO2 related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO2. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO2 content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO2 and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed. |
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