170 R. L. BERG 



the early stages of embryonic life in land animals and some plants, also the 

 adaptation of gametes to movement through an aqueous medium and (3) the 

 marine nature of the earliest sedimentary deposits of biogenic origin. 



The similarity in the salt composition of the waters of the ocean and that of 

 the body fluids of land animals could be accounted for, as Vernadskiï explained 

 in 1921, by a parallel accumulation of salts in the organism and in the sea water, 

 although the mechanism of this accumulation and regulation is completely 

 different in the two cases. 



The indispensabihty of water for the processes of fertilization shows, at most, 

 that the ancestors of the group of animals or plants in question lived in an 

 aqueous medium, but this fact must not be regarded as proof that life originated 

 in the ocean. In most plants the pollen cannot even endure moistening. The nuclei 

 of the pollen tube making their own ways into the ovarian sac of angiosperms 

 do not constitute a locomotor apparatus like the locomotor apparatus of sper- 

 matozoa. As Gerassimova-Navashina has shown, the forces which repel these 

 nuclei from one another are similar to those which act in every mitotic division 

 of a cell. 



The presence of the external skeletons which make up the strata of sedimentary 

 formations demonstrate the secondary nature of the creatures which gave rise 

 to these formations. The exoskeleton is, in essence, a screen. The first inhabi- 

 tants of the Earth are supposed to have had no exoskeletons. We must also 

 remember that land organisms leave less recognizable remains than do marine 

 organisms. Clearly, not one of the arguments used in favour of the exclusively 

 marine origin of Hfe vvdll withstand criticism. 



The most serious consideration which excludes, not merely all open waters, 

 but also the whole surface of the land, from having been the seat of biopoiesis 

 was put forward by L. S. Berg in 1947. He stated that, at present, life is protected 

 from the harmful effects of ultraviolet radiation by the so-called 'ozone screen'. 

 Free oxygen serves as a shield for living things. However, there was no oxygen 

 in the primaeval atmosphere. Living things are the only sources which could 

 bring about a constant oxygen content in the atmosphere. L. S. Berg poses the 

 question: What protected living things from short-wave radiation during their 

 development ? 



The idea of something which served the purpose of the ozone screen thus came 

 forward. According to L. S. Berg, life came into being 'in the solid substrate of 

 the dry land, within the superficial layers of mechanically shattered rocky 

 formations, and there it existed, concealed from the destructive ultraviolet rays 

 while, at the same time, being accessible to the external world and to the heat 

 radiation of the Sun.' 



It was hving organisms that produced the free oxygen of the atmosphere and 

 only then did they colonize the dry land and open water. 



At present we have some reason to beUeve that there is a constant source of 

 free oxygen in the atmosphere itself and that there are, or once were, analogues 

 of the ozone screen, not only in the lithosphère, but also in the hydrosphere and 

 atmosphere. 



According to Urey, short-wave radiation played a decisive part in the evo- 



