466 Annals New York Academy of Sciences 



alternative, but rather complementary, approaches to the study of the forma- 

 tion of organic compounds on the abiotic earth.^^'** In fact, they represent 

 progressive stages in the development of the earth. An important condition 

 which is common to all of these models is thai they are essentially reducing or 

 at least nonoxidizing in character, of which we have cosmochemical^"-^' and 

 geochemical^- evidence. Additional evidence for the reducing conditions of 

 the atmosphere of magmatic origin is provided by the fact that the terrestrial 

 rate of oxygen production by photolysis of water is less than the rate of vol- 

 canic carbon monoxide production.*^ 



Energy Sources 



Several sources of energy were available for the synthesis of organic com- 

 pounds during the transformation of the Earth from protoplanet into planet. 

 The main source was, of course, the sun providing ultraviolet light and ion- 

 izing radiation at a rate 10^ times as high as that observed at the present time.^* 

 A second source was the earth itself with its natural radioactivity^^ ■*■* and the 

 heat derived from gravitational compression and radioactivity.^^ 



However, I wish to emphasize that if, as indicated above, some of the primor- 

 dial constituents of the earth protoplanet were radicals or reactive chemical 

 compounds, then organic synthesis could have occurred spontaneously at 

 relatively low temperatures during the melting of the protoplanetary ices in 

 the absence of highly activating forms of energy. It is surmised that these 

 spontaneous syntheses were responsible for the formation of substantial 

 amounts of organic and biochemical compounds. Furthermore, due to the rela- 

 tively low prevailing temperatures and the reducing conditions of the proto- 

 planetary environment, the compounds thus formed would have been pre- 

 served for very long times. 



During the further stages of geological development additional sources of 

 energy were available on the surface and atmosphere of the earth. It is 

 likely that in addition to ultraviolet light and ionizing radiation, electric 

 discharges and the heat from plutonic processes contributed also to the forma- 

 tion of organic compounds. 



Synlliesis of Amino Acids and Hydroxy Acids 



The synthesis of amino acids and hydroxy acids under possible primitive 

 Earth conditions has been accomplished by several investigators who used 

 electrical discharges, ultraviolet light, and ionizing radiation. Moreover, 

 when some of the reactive carbon compounds detected in comets were used, the 

 formation of amino acids and hydroxy acids was observed to occur spon- 

 taneously at moderate temperatures. 



(/) By electric discharges. In particular, Loeb,** Miller, *^"*^ Hough and 

 Rogers,*^ Abelson,^'' Heyns e/ a/.,''^ Pavlovskaya and Pasynskii,*^- Franck,^^ and 

 Oro and Engberg,^'' applied silent and spark discharges to aqueous mixtures of 

 totally reduced (CH4 , NH3) or partially oxidized carbon and nitrogen com- 

 pounds. The products obtained include the amino acids glycine, alanine, 

 (3-alanine, sarcosine, a-amino-n-butyric acid, a-aminoisobutyric acid, glutamic 

 acid, aspartic acid, valine, and leucines, and the hydroxy acids glycolic, lactic, 

 succinic and hydroxybutyric. 



