Boundaries of the earth's biosphere

Abstract

We estimated the boundaries of the Earth's biosphere using the presentations developed earlier by authors of the new physical thermo-vacuum mechanism which causes irreversible (“explosive”) damage to vegetative cells and spores of microorganisms under space vacuum conditions around the Earth (M. D. Nussinov and s. V. Lysenko, JBIS, 42, 431 (1989)). As the consequences of this mechanism, which are based on experimental testing, the conditions of microorganisms may be written as set of inequalities: Pe^PsH₂O(I), Pe>PsH₂O (2) and Te^S_c(3), where: Pe-environmental (ambient) pressure; Ps_H2O-water vapour pressure; Se-environmental (ambient) temperature and Sc-critical temperature for H₂O (Sc≈160°C). These inequalities allowed us to estimate roughly the upper (in atmosphere) (H atm) and the lower (in Earth's interior) (H int), boundaries of biosphere. The estimation gives the H atm value <100 km. This estimation was confirmed from two series of measurements of microorganisms sampled in the upper atmosphere with high-altitude sounding rockets [(S. V. Lysenko, Advanced Microbiology, 16, 231, (1981) (in Russian)]. Approximate agreement between predicted and experimental results is observed. From H > 80 to 90 km no microorganisms were observed in the rocket traps. Therefore, to a first approximation H atm ≈ 100 km. The lower boundaries for Pe and Se conditions clearly correspond to H int ≈ 30 km below the Earth's surface, at the Moho layer and some deeper.

These conditions may help to explain the existence of thermophilic microorganisms discovered recently in the “black smokers” of the deep-sea bottom, i.e., in regions at high pressure and temperatures. We concluded that the cells of microorganisms able to reach Earth orbit due to light pressure action or other means, e.g., from space or on outer surfaces of space probes, would be heated quickly by IR sunlight up to S ≈ 400 K (considering a microbial cell as a black body) and would quickly explode. Therefore, both space vacuum and ionizing space radiations are serious obstacles to radiopanspermia and throw doubt on the comet hypothesis.

Conditions (1) to (3) may be considered suitable for a rough estimation of the possibility of primitive microbial life on other worlds. For example, this fact may be indicative of the absence of microbial life on the surface of Venus where Te ≈ 500°C (i.e. higher than Tc) and pressure is high (Pe ≈ 100 atm). As to Mars then, the conditions (1) to (3) also give reason to doubt the possibility of primitive microbial life on its surface because the diurnal temperature difference is ΔT ≈ 100°C with T_max ≈ 27°C. Then with the pressure on Mars surface P ≈ 5 torr, conditions (1) to (3) are not satisfied.