MICROBE AND LIFE 



postulated to have occurred such that they represent a continuity 

 with the essential expressions of life as are known to us to-day. An 

 adequate solution of this problem obviously requires the cooperation 

 of exponents of many divergent fields of science. 



I shall now attempt to draw a sketch of ideas that have been devel- 

 oped in this connexion, but before doing so I wish to mention that 

 the outlines of the picture have been developed by many scientists 

 amongst whom I shall name only such outstanding contributors as 

 Haldane, Oparin, Horowitz, Bernal, Urey, and H.J. Muller. I, for 

 my part, cannot refrain from including some concepts derived from 

 studies of microbial metabolism. 



Let us begin by consulting the astronomers who recently have ad- 

 vocated the view that the earth owes its origin to an agglomeration of 

 small solid particles, previously formed in the primeval nebula from 

 which our planetary system was born. Such an agglomeration must 

 have led to a considerable increase in temperature, in consequence of 

 which the earth initially must have appeared as a blazing liquid 

 sphere. In his recent interesting discussion of the origin of our atmos- 

 phere our fellow-member, Berlage, has concluded that the earth's 

 mass is too small to have prevented, at the existing high temperatures, 

 the escape into interstellar space of an important part of the gases that 

 at first surrounded it. Consequently an atmosphere, later developing 

 after a period during which the earth became progressively cooler, 

 must be of secondary origin, and have arisen from gases emanating 

 from the earth's crust itself. However, the composition of this second- 

 ary atmosphere must have been quite different from that of our present 

 atmosphere. 



Especially the geochemist, Urey, has advanced forceful arguments 

 in favour of the view that the most important components were hydro- 

 gen, methane, water, ammonia, and hydrogen sulphide. That is to 

 say that there occurred in this atmosphere, besides hydrogen, the 

 elements carbon, oxygen, nitrogen, and sulphur in their most com- 

 pletely hydrogenated state. During prolonged cooling a large part of 

 the water must have condensed, and thus occasioned the coming into 

 existence of the oceans that cover the greater part of the earth. 



Gradually the earth's surface reached a temperature range within 

 which life may have made its appearance upon the earth. It is, how- 

 ever, imperative to reject the idea that such life would have exhibited 



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