**5. The impact of redox carbon cycle on the rate of biodiversity**

It is a known fact in geological history that in the past there were "explosions" of life and mass extinctions of living organisms. In some works, a periodicity in a rate of change of biodiversity (a rate of appearance of the new fauna and flora species per geological unit) in time was revealed [24]. Following the redox carbon cycle model, these facts can be reasonably explained. It was supposed that periodicity is caused by the increase of oxygen concentration in the Phanerozoic atmosphere [25]. The assumption was supported by a close coherence of the curves illustrating the time dependence of a rate of change of biodiversity and other parame‐ ters, strongly related with oxygen concentrations. The peaks of all curves fully coincided and corresponded to oxygen maximum (see Figure 7 from [25])

The physical sense of this link is quite clear. The elevated O2 concentrations in the atmosphere stimulate (photo)respiration in photosynthesizing organisms, which is followed by superoxide radical formation. They attack gene molecules causing mutations. Though in a cell there are some enzymes, which destroy radicals reducing them to H2O and O2, at the time of oxygen growth, the enzymes fail to cope with the abundance of radicals and to diminish their amount to the safe level. As a result, mutations appear and the rate of change of biodiversity increases. Rothman [26] found a good correlation of *ε* parameter and the rate of change of biodiversity for land plant families as well as for marine animals. His results prove the relation of orogenic cycles and biodiversity rate.

**4. The effect of redox carbon cycle on the climate in the past**

bution of other greenhouse gases.

62 Applied Photosynthesis - New Progress

The role of CO2 in climate formation is a well-known fact. It is the main component of "greenhouse" gases [20]. The periodic filling of the "atmosphere–hydrosphere" system with CO2 in orogenic time and the following depletion of CO2 due to photosynthetic assimilation in geosynclynal period provide alternating warming–cooling change. It is even possible to use the relation between CO2 concentrations and Earth temperature for the determination of paleotemperatures [21], although the validity of this correlation is limited due to the contri‐

Following the logic of this model, the existence of climatic cycles is a result of the orogenic cycles. The beginning of the orogenic cycle may be considered as the warmest time of the cycle

The mentioned *ε* parameter may be used as the indicator of orogenic and climatic cycles. At the beginning of the orogenic cycle, when CO2/O2 ratio is maximal and the contribution of photorespiration is low, *ε* parameter is also at its maximum and corresponds to the warming period. Conversely, at the end of the cycle, when CO2/O2 ratio is minimal and photorespiration

Popp et al. [15] found a coherence of *ε* values and climatic cycles in the Cenozoic. Hayes and others [16], having examined carbon isotope composition for more than 5000 samples of coeval carbonates and sedimentary organic matter spanning the Precambrian and Phanerozoic, found statistically significant differences in *ε* values in interglacial periods and those in periods of

It is a known fact in geological history that in the past there were "explosions" of life and mass extinctions of living organisms. In some works, a periodicity in a rate of change of biodiversity (a rate of appearance of the new fauna and flora species per geological unit) in time was revealed [24]. Following the redox carbon cycle model, these facts can be reasonably explained. It was supposed that periodicity is caused by the increase of oxygen concentration in the Phanerozoic atmosphere [25]. The assumption was supported by a close coherence of the curves illustrating the time dependence of a rate of change of biodiversity and other parame‐ ters, strongly related with oxygen concentrations. The peaks of all curves fully coincided and

The physical sense of this link is quite clear. The elevated O2 concentrations in the atmosphere stimulate (photo)respiration in photosynthesizing organisms, which is followed by superoxide radical formation. They attack gene molecules causing mutations. Though in a cell there are some enzymes, which destroy radicals reducing them to H2O and O2, at the time of oxygen growth, the enzymes fail to cope with the abundance of radicals and to diminish their amount to the safe level. As a result, mutations appear and the rate of change of biodiversity increases.

and the end as the coldest one. The latter is often accompanied with glaciations.

increases, *ε* parameter reaches its minimum and corresponds to the cooling period.

glaciations. The results were supported by other researchers [22, 23].

corresponded to oxygen maximum (see Figure 7 from [25])

**5. The impact of redox carbon cycle on the rate of biodiversity**

The observed periodicity of mass extinctions of plant and animal species on the Earth has a close agreement with the previous correlation. These events are also linked with a change of CO2/O2 ratio in the atmosphere over time [27]. According to the model, the abrupt change of CO2/O2 ratio in the atmosphere occurring in orogenic cycles' transitions should lead to the extinction events, because they are followed by the change of aerobic conditions to anoxic ones causing a mass extinction of aerobic organisms.
