The Origin of Life 



present atmosphere its oxidizing character, came from two sources: 

 Part had a photochemical origin (from water undergoing photolysis 

 in the upper atmosphere, with the hydrogen escaping into space)- 

 the rest was produced photosynthetically by living organisms (the 

 main source today). 



Fig. 1.1 I Spark-discharge apparatus. 



( After Miller, 1957, Ann. N.Y. Acad. Sci. 69. ) 



In addition to the abiogenic formation of organic compounds as 

 outlined above, simple organic compounds are formed by the inter- 

 action of water vapor with carbides in magma brought to the sur- 

 face by volcanic activity (3Fe,„C„ -|- 4mHoO = Fe.{04 + C;i„H,sm). 

 Calvin and others have shown in experiments with ionizing radia- 

 tions (of the sort that would be produced by radioactive materials 

 or by cosmic rays) that, in the presence of molecular hydrogen, 

 partial reduction of carbon dioxide can occur. Further irradiation of 

 aqueous solutions of the substances produced (formic acid, formal- 

 dehyde ) leads to the formation of compounds such as oxalic acid or 

 acetic acid. Eventually molecules of two-carbon compounds (acetic 

 acid) may combine to produce a four-carbon compound (succinic 

 acid). In these experiments amino acids also are produced. 



In other experiments, Fox has shown that heating dry amino acid 

 mixtures results in the formation of synthetic polypeptides (pro- 



