Life: Its Nature and Origin 45 



comparable amounts of the many much less reactive organic salts 

 and acids. 



In summary, the miniature physico-chemical universe called the 

 living cell, if situated in its proper environment, ticks along auto- 

 matically like a watch, first growing and finally dividing into two 

 daughters, each like the original and each automatically repeating 

 the processes of growth and reproduction. 



ORIGIN OF LIFE 



A plausible explanation for the origin of life must account for three 

 items : ( 1 ) the simple elements or molecules of the pre-biological 

 world which formed the building blocks for life, (2) a logical set 

 of chemical reactions which would lead to the formation of life, 

 and (3) a source of nutrient materials for the persistence of life. 



Available Materials 



As was indicated in Chapter 1, there has been considerable con- 

 troversy about the pre-biological composition of the atmosphere 

 and the oceans, but most authors agree that the atmosphere con- 

 tained little or no oxygen and was essentially a reducing or at least 

 a non-oxidizing medium. It probably contained chiefly water vapor, 

 carbon dioxide, and nitrogen, with small quantities of hydrogen 

 sulphide, methane, and ammonia. The oceans probably contained 

 dissolved carbon dioxide, ammonia, and hydrogen sulphide, with 

 various metallic compounds, chlorides, and phosphorus compounds 

 in solution. 



Pre-biological Syntheses 



Oparin (1938) believed that, during a time when atmospheric 

 temperatures were from 300°C to 1,000°C, a certain proportion 

 of these compounds would combine to form simple hydrocarbons 

 such as acetylene and that later, when the oceans formed, they 

 would contain quantities of these hydrocarbons in solution. 



In 1953 S. L. Miller pumped a mixture of ammonia, methane, 

 water vapor, and hydrogen (the mixture believed by Urey to 

 constitute the primeval atmosphere) past an intermittent electric 

 discharge and found that at the end of a week the condensed water 

 vapor had become red and turbid. On analysis, the products proved 

 definitely to contain three amino acids, glycine, a-alanine, and 

 ^-alanine, and possibly a fourth, aspartic acid. Because amino acids 



