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Revival of the concept of the cold prehistory of life

The extra-terrestrial scenario of the origin of life suggested by Svante Arrhenius (1908) as the ‘panspermia’ hypothesis was revived by the discovery of a low-temperature quantum limit of a chemical reaction rate in 1973. Entropy factors play no role near absolute zero, and slow molecular tunnelling can lead to the exothermic formation of quite complex molecules. Interstellar grains or particles of cometary tails could serve as possible cold seeds of life, with acetic acid, urea and products of their polycondensation as quasi-equilibrium intermediates. Scenarios of the origin of life should consider the appearance of a typical feature of living species—chiral purity of their aminoacids and sugars. Very cold solid environment hinders tunnelling racemization under conditions typical for outer space. However, the decisive problem of the origin of chiral purity of the Earth's biosphere is the mechanism of the spontaneous breaking of mirror symmetry rather than the search for some ‘advantage factors’ which can promote gradual accumulation of enantiomeric excess. Extra-terrestrial (cold, solid phase) scenarios of the origin of life seem to be more promising from that point of view than terrestrial (warm) scenarios. In a scheme of five main stages of prebiological evolution some problems important for further investigation are briefly discussed.