4 The Nature of Biological Diversity 



fate.*) The ahundances of some elements in the terrestrial surface 

 regions are given also in Tahle 1. It will be noted that hydrogen is 

 present mostly in oxidized form as water and that carbon and nitrogen 

 are far less abundant than oxygen in surface water and even less 

 abundant relative to oxygen in igneous rocks. Terrestrial surface car- 

 bon is present mostly as carbonates, i.e., in the highest oxidation state. 

 If one added a small amount of hydrogen to the earth, one would 

 expect that carbon and nitrogen would be converted in time to 

 methane and ammonia and all sulfates would be reduced to sulfides. 



Table 1. Atomic abundances of some elements relative to oxygen 



* The carbon abundance is that of the sedimentary rocks relative to oxygen in the 

 oceans. The abundances of the mineral elements in sedimentary rocks are similar 

 to those in igneous rocks. 



sources: Sun: L. Goldberg, E. A. Miiller, and L. H. Aller. Astrophys. J., Suppl. 

 Ser. 5:1-138 (1960). Earth: K. Rankama and T. G. Sahama, Geochemistry, Univer- 

 sity of Chicago Press, Chicago (1950). 



It is evident that two important processes from the standpoint of 

 the present discussion have occurred on the earth and also on Mars 

 and Venus. (1) The more volatile fraction of solar matter has been 

 lost to a high degree, including the elements H, N, C, and O, and the 

 inert gases. (2) The surface regions of these planets have become 

 highly oxidized. The first process is veiled in the obscurity of the 

 earth's origin. Since any discussion of the process would carry con- 

 siderable doubt and would be very long and involved, it will not be 

 treated here. The second process is well understood. Oxidation of the 

 earth is probably continuing at the present time and is due to the 

 escape of hydrogen from the earth into space. The same process can 

 reasonably be supposed to have occurred in the case of Mars and 



* E. Du Fresne, Dissertation, University of Chicago, 1960. 



