856 MILLER [chap. 32 



of amino acids by the action of ultraviolet light on a 2.5% formaldehyde 

 solution containing ammonium chloride. These high concentrations of formalde- 

 hyde would not have occurred on the primitive Earth. It would be interesting 

 to see if similar results could be obtained with 10~4-10~5 m formaldehyde. This 

 type of experiment deserves further investigation, 



C. Radioactivity and Cosmic Rays 



Because of the small amount of energy available, it is highly unlikely that 

 high-energy radiation could have been very important in the synthesis of 

 organic compounds on the primitive Earth. However, a good deal of work has 

 been done using this type of energy, and some of it has been interpreted as 

 bearing on the problem of the origin of life. 



Dose and Rajewsky (1957) produced amines and amino acids by the action of 

 X-rays on various mixtures of CH4, CO2, NH3, N2, H2O and Ho. A small yield 

 of amino acids was obtained by the action of 2 MeV Van de GraafF electrons on 

 a mixture of CH4, NH3 and H2O (Miller, unpublished experiments). 



The formation of formic acid and formaldehyde from carbon dioxide and 

 water by 40 MeV helium ions was mentioned previously. These experiments 

 were extended by using aqueous formic acid (Garrison, Morrison, Haymond and 

 Hamilton, 1952). The yield per ion pair was only 6x 10~4 for formaldehyde 

 and 0.03 for oxalic acid. Higher yields of oxalic acid were obtained from 

 Ca(HC03)2 and (NH4)HC03 by Hasselstrom and Henry (1956). The helium 

 ion irradiation of aqueous acetic acid solution gave succinic and tricarbolic 

 acid along with some malonic, malic and citric acids (Garrison et al., 1953). 



The irradiation of 0.1 and 0.25% aqueous ammonium acetate by 2 MeV 

 Van de Graaff electrons gave glycine, aspartic acid and a third compound, 

 probably diaminosuccinic acid (Hasselstrom, Henry and Murr, 1957). The yields 

 were very small. Massive doses of gamma rays from cobalt-60 on solid am- 

 monium carbonate yielded formic acid and very small quantities of glycine and 

 possibly some alanine (Paschke, Chang and Young, 1957). 



The concentrations of carbon compounds and dose rates in the above ex- 

 periments were very much larger than could be expected on the primitive Earth, 

 and the products and yields may depend markedly on these factors, as well as 

 the effect of radical scavengers such as HS"", and Fe2+ and ¥e^+. It is difficult to 

 exclude high-energy radiations entirely, but if one is to make any interpretations 

 from laboratory work, the experiments should be performed at much lower 

 dose rates and concentrations of carbon sources. 



D. Thermal Energy 



The older theories of the formation of the Earth involved a molten Earth 

 during its formation and early stages. These theories have been largely aban- 

 doned, since the available evidence indicates that the solar system was formed 

 from a cold cloud of cosmic dust. The mechanisms for heating the Earth are the 



