The Big Bang of the Ecosphere

About 3 billion years ago the atmosphere started to transform from a reducing to an oxidizing environment as evolution developed oxygenic photosynthesis as key mechanism to efficiently generate free energy from solar radiation (Buick, 1992; Des Marais, 2000; Xiong and Bauer, 2002; Renger, 2008; Rutherford et al., 2012; Schmitt et al., 2014a). Entropy generation due to the absorption of solar radiation on the surface of the earth was retarded by the generation of photosynthesis, and eventually a huge amount of photosynthetic and other complex organisms developed at the interface of the transformation of low entropic solar radiation to heat. The subsequent release of oxygen as a “waste” product of photosynthetic water cleavage led to the aerobic atmosphere (Kasting and Siefert, 2002; Lane, 2002; Bekker et al., 2004), thus opening the road for a much more efficient exploitation of the Gibbs free energy through the aerobic respiration of heterotrophic organisms (for thermodynamic considerations, see (Renger, 1983; Nicholls and Ferguson, 2013)).

From the very first moment this interaction with oxygen generated a new condition for the existing organisms starting an evolutionary adaptation process to this new oxidizing environment. ROS became powerful selectors and generated a new hierarchy of life forms from the broad range of genetic diversity in the biosphere. We assume that this process accelerated the development of higher, mainly heterotrophic organisms in the sea and especially on the land mass remarkably.

The efficient generation of biomass and the highly selective impact of ROS lead to a broad range of options for complex organisms to be developed in the oxidizing environment. Important and more complex side effects next to the direct destructive impact of ROS are examples like the fact that the molecular oxygen led to generation of the stratospheric ozone layer, which is the indispensable protective shield against deleterious UV-B radiation (Worrest and Caldwell, 1986). ROS lead to new complex constraints for evolution that drove the biosphere into new directions - by direct oxidative pressure and by long range effects due to environmental changes caused by the atmosphere and the biosphere themselves.

For organisms that had developed before the transformation of the atmosphere the pathway of redox chemistry between water and O2 by oxygenic photosynthesis was harmful, due to the deleterious effects of ROS. It is assumed that about 90% of all living organisms died due to the impact of ROS in that period of earth history making the big bang of the biosphere, understood as the development of oxygenic photosynthesis, the most deleterious environmental change ever with its subsequent selection pressure. O2 destroys the sensitive constituents (proteins, lipids) of living matter. As a consequence, the vast majority of these species was driven into extinction, while only a minority could survive by finding anaerobic ecological niches. All organisms developed suitable defence strategies, in particular the cyanobacteria, which were the first photosynthetic cells evolving oxygen (Zamaraev and Parmon, 1980).

 
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