52 



THE BIOLOGICAL APPROACH 



could penetrate through the atmosphere to the surface of the earth. 



This is no mere theoretical possibility: experiments have in later 

 years proved that mixtures of gases such as given in Fig. 8 can yield 

 many different 'organic' compounds when treated with water in glass 

 vessels by strong electrical sparks or by irradiation with short ultra- 

 violet rays, the only pre-requisite being the absence of free oxygen. 

 The best known experiments are those by Miller (1959, 1960), who 

 succeeded in producing amino-acids in this way. Moreover, Wilson 

 (1960) recently reported how even far larger molecules could be 

 formed under similar conditions. 



A schematized drawing of the spark discharge apparatus used by 

 Miller is given in Fig. 9. Electrical sparks are used for convenience. 

 Their energy is smaller than can be obtained by irradiation with 

 shorter ultraviolet light, but they present fewer experimental diffi- 

 culties. The small flask in the lower left-hand corner contains water, 

 whilst the rest of the system contains, say, a mixture of hydrogen, 

 methane and ammonia. The water is boiled, the spark is operated 



25 



50 75 

 Time, 



100 



125 150 



Fig. 10. Concentrations of ammonia, hydrogen cyanide and aldehydes 

 in the U-tube, and amino-acids in the 500 ml flask, while sparking a 

 mixture of methane, ammonia, water and hydrogen in the apparatus of 

 Fig. 9 (from S.L.Miller, 1959). 



