INFLUENCE OF ULTRAVIOLET LIGHT 63 



ARADIATIC FOR SHORTER ULTRAVIOLET LIGHT 



Moreover, there is, at present, our anaerobic life, which is also an- 

 oxygenic. We do not yet know whether, in the anoxygenic period, 

 there was also anaerobic (and anoxygenic) life, similarly excluded 

 from the primeval atmosphere. There is, however, a probability that 

 the early life forms which developed organic photosynthesis and 

 assimilation, were under disadvantages more or less comparable to 

 those anaerobic life is exposed to at present. 



Organic assimilation will then probably have been based on pro- 

 tein, as it is now. Proteins, however, now are non-resistant to radia- 

 tion of the shorter ultraviolet light, which then still reached the 

 surface of the earth. Hence it is quite possible that the early forms 

 of present-day life, the early ancestors of the group that later took 

 full ascendancy, were limited at the beginning to a set of very narrow 

 environmental conditions, comparable in a sense to the restrictions 

 imposed upon our present-day anaerobic life. They were, of course, 

 not anaerobic, because the atmosphere as such was not harmful at 

 the time. They might, however, well have been aradiatic for the 

 shorter ultraviolet light, if it is permissible to introduce this term. 

 They may have been limited at first to the hydrosphere, living in 

 rivers, lakes or oceans at such a depth that the 'thin soup' had 

 filtered out the obnoxious shorter ultraviolet light, whereas the red 

 part of the spectrum, penetrating much farther and so important to 

 organic photosynthesis, was still available to them. Again, they might 

 have lived in pores in the soil, in free communication with fresh air, 

 but shielded from direct sunlight. Of course, such considerations are 

 quite hypothetic, but knowing the prolific variation life is capable 

 of attaining, it is quite possible that some of the earliest forms capable 

 of organic photosynthesis and being aradiatic for the shorter ultra- 

 violet light, lived in the early hydrosphere, and others in pores of 

 the soil. 



PRE-ACTUALISTIC AND ACTUALISTIC 



The difference between the two atmospheres lies not only in having 

 or not having free oxygen, but also, as a direct consequence, in 

 whether the shorter ultraviolet light is kept from reaching the surface 

 of the earth, or not. Taken together, I think that these differences 

 between the primeval atmosphere and the present one are so im- 



