THE GENEJiAL ENVIRONMENT 



75 



left a relatively rarefied atmosphere that 

 was probably free from oxygen and, there- 

 tore, from ozone. 



There is a fair possibility that the early 

 atmosphere did lack oxygen and that the 

 gases then present did not act as effective 

 screens for ultraviolet radiation. If the sun's 

 full ultraviolet spectrum did reach the pri- 

 meval earth, some possible effects include 

 the following: 



1. Under the influence of photochemi- 

 cally active radiations, the relatively inert 

 chemicals dissolved in the oceans might 

 well have formed increasingly complex or- 

 ganic compounds with varied colloidal 

 structures until, finally, Hving substance it- 

 self was synthesized. This photochemical 

 hypothesis avoids certain difficulties im- 

 posed by the more usual postulation of a 

 theiTnal activation of the beginning of Ufe. 

 It is pertinent that ultraviolet radiation is 

 reported to effect the synthesis of carbo- 

 hydrates from carbon dioxide and watei 

 without the aid of chlorophyll (Baly, 

 1929). Radiations of comparable wave- 

 length acting on modern genes accelerate 

 the rate of mutation. Hence, perhaps, we 

 could expect more rapid evolution in an 

 environment in which they were effectively 

 present in graded intensities. 



2. If the initial hving material so formed 

 was similar to present day protoplasm, it 

 could have remained aUve only in or near 

 the shadows cast by objects Hke rocks that 

 are opaque to these shorter solar radiations, 

 or in other niches where the newly formed 

 life would not have been exposed for the 

 whole day to the action of the lethal rays. 

 Water could have furnished suitable pro- 

 tection only where it was very deep. It 

 follows that the presence of such abiotic 

 rays above the protecting umbrella of the 

 earth's atmosphere would probably, then as 

 now, kill cysts and spores that might be 

 drifting through interplanetary space. It 

 may be recalled that the theory of the ex- 

 tramundane origin of the ancestors of all 

 Ufe now found on the earth has been sup- 

 ported by various outstanding scientists, the 

 chemist Arrhenius among them. Photo- 

 chemical considerations are strongly op- 

 posed to such a possibility. 



The change in the ultraviolet spectrum, 

 after the production of the oxygen-ozone 

 atmospheric screen, would account for the 

 apparent absence of spontaneous genera- 

 tion of life on the earth today when theory 



apparently demands such an origin at some 

 time in the remote past. This whole fine 

 of speculation assumes that the oxygen now 

 in our atmosphere has been largely pro- 

 duced by pholosynthetic activity of plants 

 and, hence, that fife itself has played an 

 important role in estabUsliing its modern 

 environment. These particular speculations 

 are developed further by Hutchinson 

 (1944) and Giese (1945), who cite many 

 key references. 



Oparin (1938) marshalls the evidence 

 indicating that fife evolved on the etirth 

 from simple inorganic materials. According 

 to his reconstruction, the sUghtly cooled 

 earth had a central molten core containing 

 metals acquired originally from the sun. 

 The core was surrounded by "a membrane 

 of primary igneous rocks" and enveloped in 

 an atmosphere made up in the main of 

 superheated steam. Oxygen and carbon 

 dioxide were not present in the original 

 atmosphere, but developed secondarily. 

 Carbon itself first appeared as carbide of 

 iron and other metals, all coming from the 

 parent sun. According to these views, 

 hydrocarbons arose from the action of water 

 on the metalhc carbides. Nitrogen also ap- 

 peared on the earth in the reduced state, 

 probably as ammonia. 



Oparin summarized the essence of his 

 argument as follows (p. 126): 



"Hydrocarbon derivatives such as alcohols, 

 aldehydes, organic acids, amines, amides, etc., 

 undergo important transformations when tlieir 

 aqueous solutions are allowed to stand. In these 

 solutions the dissolved substances undergo re- 

 actions of condensation and polymerization, as 

 well as oxidation-reduction reactions; in other 

 words, every type of change occurring in the 

 living cell. As a result, numerous high molec- 

 ular compounds, similar to those present in 

 living cells, may appear in aqueous solutions of 

 hydrocarbon derivatives on long standing." 



From these, given more time, comes the 

 origin of primary colloidal systems and 

 finally of organisms. 



Living protoplasm is not adjusted to 

 meet the extreme conditions known to exist 

 within our solar system. Environmental ex- 

 tremes must not be too great, and the 

 transition from one extreme to another must 

 not be too sudden. With life based pri- 

 marily on water as ours is, the temperature 

 for active metabolism can range only a few 

 degrees below to a few tens of degrees C. 



