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the pioneering formulations of the Russian chemist, Oparin, scientists 

 from many disciplines have begun to do experiments designed to test 

 specific hypotheses concerning the origin of life. 



Oparin proposed that life originated on earth at a time when the seas 

 were rich nutrient soups full of complex organic molecules. He devel- 

 oped a detailed scheme for the chemical evolution of more and more 

 complex compounds, beginning with the gases thought to be present in 

 the atmosphere when the earth cooled down — methane, ammonia, water, 

 and hydrogen. Subsequently, following a different line of reasoning, 

 Urey came to similar conclusions about the reducing atmosphere of the 

 earth at this time, and proposed that the formation of organic compounds 

 might be catalyzed by ultraviolet light and by electric discharges in 

 storms. In the absence of free oxygen, there would have been no screen- 

 ing of the high-energy short-wave-length ultraviolet radiation from the 

 earth by the ozone layer of the atmosphere, as there is now. 



The first experimental demonstration of the origin of simple amino 

 acids and other organic molecules under conditions similar to those 

 postulated by Urey was carried out by circulating hot water in an atmos- 

 phere of hydrogen, methane, and ammonia, with energy provided by a 

 spark discharge. The products, separated by chromatography and char- 

 acterized chemically, included several straight-chain amino acids and 

 other organic acids, as well as carbon monoxide, carbon dioxide, and 

 nitrogen in the gaseous phase. Recently adenine too has been formed in 

 such a system. Attempts to synthesize other aromatic compounds such as 

 pyrroles and pyrimidines, have not yet succeeded, but it seems likely that 

 with the proper choice of conditions, including the presence of trace 

 metals and surface catalysts, ring compounds characteristic of biological 

 material will be formed. These experiments, and similar ones performed 

 subsequently in other laboratories, have established the principle that 

 organic compounds can arise in the absence of life under conditions fairly 

 similar to those existing while the earth was cooling. 



Although the huge organic solution existing then would tend toward 

 disorder, the direction may have been reversed, rarely and locally. For 

 example, the adsorption of materials on clay surfaces is thought to have 

 accounted for the presence of only one of the optically active isomers of 

 many compounds, and at just such sites the necessary initial organiza- 

 tion may have been conferred upon the organic world by the pattern of 

 inorganic templates. The fact that these early reactions occur in the 

 absence of oxygen is of great importance. If oxygen had been present in 

 the atmosphere preceding the origin of life, there would have been two 

 disastrous consequences: the compounds being formed would have been 

 oxidized and lost; and an ozone layer would have accumulated in the 



