ORIGIN OF ORGANIC PHOTOSYNTHESIS 59 



his experiments succeeded in producing macromoleculcs after in- 

 troducing H'iS into his mixture. So the presence of sulphur might 

 have been an important factor in those early days. 



A further step will have been that various kinds of these bigger, 

 'growing' molecules became dominant. From this stage to life-like 

 compounds with specific metabolistic processes and capable of pro- 

 pagation, is, of course, another step requiring a great number of 

 separate reactions. However, it is a step which, although taken in a 

 gradual way by a large number of separate reactions, is quite well 

 conceivable from our present knowledge of both inorganic and 

 organic chemistry. 



MUTANTS ACQUIRING A NEW SKILL: ORGANIC PHOTOSYNTHESIS 



Life in that early time, still under the primeval atmosphere, even 

 then must have produced mutants. For mutation is something akin 

 to those larger molecules of 'organic' composition. Although still not 

 well understood, mutation is the result of some minor switch-over 

 in local structure of one of the small building blocks of a large 

 molecule; a switch-over due to some energy flux, probably mostly 

 external, which might be of thermal or radiative character. 



Somewhere, sometime, mutations of that early life will have pro- 

 duced compounds capable of organic photosynthesis, i.e. of organic 

 assimilation. They acquired the unique capability of dissociating 

 carbon dioxide (CO2) into carbon (C) and free oxygen (O2). The 

 carbon may be used to build more organic matter for the living 

 organism, whilst the oxygen escapes into the atmosphere. 



The results of this new capability of early life have been complex, 

 and in the end overwhelming. The first benefit of organic photo- 

 synthesis was not so much in the easy acquisition of carbon to build 

 more living matter, but in the much greater energy freed by this 

 process, when compared to the anaerobic metabolism. Any such 

 reactions in which free oxygen is not involved, such as those of 

 nitrate-, sulphate- or carbonate-reducing bacteria, have a much lower 

 energy production than freed by the assimilation of carbon dioxide. 

 The new way of life consequently gave an immediate advantage in 

 the struggle for life over those contemporary organisms which were 

 still based on earlier metabolism. 



