Normal biogeochemical cycles are not closed, although the degree of reversibility of annual cycles of the most important biogenic elements reaches 95–98%. Incomplete reversibility (openness) is one of the most important properties of biogeochemical cycles, which has planetary significance. This is what caused the biogenic accumulation of oxygen and nitrogen in the atmosphere, various chemical elements and compounds in the earth’s crust. For example, due to the incomplete reversibility of the carbon cycle over the past 600 million years, huge reserves of carbon deposits (limestone, bitumen, coal, oil, etc.) have accumulated, estimated at 1016–1017 tons.
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