58 THE BIOLOGICAL APPROACH 



tion of life can be represented by a double cone. The lower one 

 symbolizes the early mode, of life with its great number of elements 

 participating in inorganic photosynthetic and allied processes in the 

 primeval atmosphere without free oxygen. The upper cone represents 

 the development of present life, with a strong morphological varia- 

 tion based on a certain group of narrowly limited biochemical re- 

 actions under the new oxygenic atmosphere. 



From the first inorganic photosynthetic reactions occurring under 

 the primeval atmosphere, which led to the formation of the 'thin 

 soup', an extremely long time elapsed before the appearance of 

 anything resembling living matter: a stretch of time filled, of course, 

 with an extremely large number of different activities. An exact limit 

 is difficult to draw. It is, perhaps, even irrelevant. It is less important 

 where to draw the dividing line between non-living and living, than 

 to retain the fundamental much more important difference existing 

 between the primeval and the new atmosphere, and, moreover, to 

 note that, as we will see, real life existed already in that primeval 

 atmosphere, life that was capable of producing if not fossils, at least 

 remains recognizable as organic products. Real life co-existed with 

 proto-life, and also with those photosynthetic reactions which one 

 should like to call inorganic by all means. Although still anoxygenic 

 in metabolism, it was a form of real life co-existing with the earlier 

 forms, with the eobionts of Pirie. 



In general, there will have been an early evolution towards bigger 

 and more complicated molecules of 'organic' substances still formed 

 by inorganic processes. These bigger molecules were normally built 

 up by smaller units, each of similar structure. They are repetitive 

 and consist of chains of identical or related blocks. Such molecules, 

 however, through small physico-chemical differences with compara- 

 ble compounds in their surroundings, are often able to incorporate 

 new blocks into their structure; or, in other words, to grow. 



Such growing will have been favoured, for certain kinds of com- 

 pounds, by the nature of their substratum; for instance, by adsorption 

 on clays or quartz, then as now, probably the two most common 

 minerals of the surface of the earth. At that time sulphides, too, will 

 have been abundant, for instance, in the form of pyrite sands. Sul- 

 phur is known for its strong catalytic properties in reactions such as 

 those under discussion. It is, for example, noteworthy that Wilson in 



