The Origin of Organic Molecules 5 



Venus. It is most improbable that hydrogen is now escaping from the 

 major planets. The general course of oxidation of carbon and nitrogen 

 expected is shown in Table 2. The compounds listed are only the most 

 simple examples. Many complex CiSOH compounds exist in which the 

 oxidation states of C and N lie between the lowest and highest oxida- 

 tion states. (The oxidation state is usually denned by counting oxygen 

 as —2 and hydrogen as -\-l and making the carbon and nitrogen states 

 such that the molecule is neutral. As is well known, the oxidation 

 states are not always uniquely determined.) The general course of 



chemical change on the earth and other terrestrial planets has been 

 from the more reduced to the more oxidized condition, i.e., from left 

 to right in the table. It is evident that a favorable condition for the 

 existence of compounds such as those required for living organisms 

 would be present during this oxidation process. 



The escape of hydrogen frtun the earth 

 and inorganic reactions involved 



It is possible to estimate the conditions for the escape of hydrogen 

 from the earth rather plausibly, though hardly with certainty. The 

 escape conditions have been given in considerable detail by Urey 

 (19591. Jeans derived the formula for the escape of planetary atmos- 

 pheres. Its application to the earth indicated a loss of hydrogen from 

 the earth considerably larger than could be accounted for by the 

 oxidation of surface elements by the oxygen left behind in the process. 

 Harteck and Jensen showed that diffusion was important and sug- 

 gested a diffusion layer at the tropopause. Subsequent work showed 

 that circulation occurred through this layer and Urey suggested that 

 the diffusion layer was at the top of the atmosphere.* The rate of 

 escape is determined by diffusion in this layer and the rate is pro- 

 portional to the surface hydrogen pressure, which at present is 10~ 

 atmosphere. The present rate was calculated as 10 7 atoms sec -1 cm" . 

 This is not a highly precise value. It is probable that the rate of escape 



* See Bates and McDowell (1957) for a discussion of the escape problem for 

 He 3 and He 4 . 



