At one time the temperature of the Sun was much lower than now. However, geologic evidence shows that even then, in the first billion years of the Earth's existence, its oceans did not freeze. The hypothesis proposed to explain this suggests that the high temperature on the planet was maintained due to the hothouse effect created by atmospheric carbon dioxide, which allows solar radiation to reach the surface of the Earth, but precludes its re-radiation back, to the outer space. But for that, no processes of conception or evolution of life in the World ocean, which began at least 3.5 billion years ago, would have been possible.

This led some scientists to the conclusion that the CO₂ content in the Earth's atmosphere during the first billion years of its existence was a thousand times more than now, amounting to approximately 39 %. The temperature in the surface layer reached almost 100°Ñ, and the water of the oceans was close to boiling point. Now, according to the deductions of these specialists, the volcanoes and volcanic rifts found in the World ocean floor annually evolve not less than 30 million tons of carbon in the form of ÑÎ₂. Another 3 to 3.5 million tons are delivered by "overland" volcanoes.

Apparently, as the internal areas of the Earth were cooling, the flow of ÑÎ₂ evolving on the surface was weakening. The total amount of carbon in the crust, oceans and atmosphere could also be reduced under the influence of the growing activity of the subduction process - the sinking tectonic plates took away with them a fair quantity of carbon.

It is supposed that geologic evolution includes cyclic processing of carbon. This is shown by the fact, well established nowadays, according to which the carbon evolving now from the depths of the Earth has the same isotope composition as the carbon contained in ancient sedimentary strata. About half of ÑÎ₂ evolved on the surface during the geologic history has already passed such cyclic "reprocessing", coming back to the depths of the Earth.

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