87 



earlier, the reduction of C0 2 to formaldehyde and methane has been 

 accomplished by the interaction of UV light with an aqueous solu- 

 tion of C0 2 and ferrous ions. In preparation for the Viking mission 

 to Mars, the reduction of C0 2 was also observed to occur on silicate 

 surfaces. The reduction of nitrogen to ammonia by titanium dioxide 

 has been accomplished, again by using UV light. 



In laboratory experiments, biomonomers have been synthesized 

 in the presence of clays. Investigations have shown that clays affect 

 the formation of amino acids and nitrogen heterocycles from CO and 

 NH 3 at temperatures of about 300°C. In addition, biomonomers can 

 be adsorbed onto clays. This adsorption provides an excellent 

 mechanism of concentration to facilitate subsequent chemical reac- 

 tions. The clay- and/or metal ion-mediated oligomerization of 

 biomonomers has also been demonstrated. Through this mechanism 

 polypeptides and oligonucleotides have been formed in higher yield 

 or with longer strands than in the absence of these inorganic compo- 

 nents. Thus, inorganic chemistry may have played an important role 

 in the emergence of life on Earth. 



POLYPEPTIDES, POLYNUCLEOTIDES, AND THE 

 BEGINNINGS OF NATURAL SELECTION 



The transition from a mixture of organic molecules to an 

 organized system that is capable of reproducing itself, represents the 

 most puzzling problem in the study of the origin of life. We know 

 that contemporary cells rely on proteins, very complex molecules, to 

 catalyze specifically almost all biological reactions, including the 

 replication and translation of nucleic acids. The proteins are them- 

 selves the products of the translation process, and their synthesis is in 

 turn dependent on the presence of preformed nucleic acids. The 

 origin of the genetic process thus appears to be a chicken-and-egg 

 problem; which came first — proteins or the coded nucleic acids? 



Not everyone agrees that studies of the origin of self-replicating 

 systems should concentrate on nucleic acids and proteins. Some 

 researchers suggest a variety of simple, alternative self-replicating sys- 

 tems. Cairns-Smith, for example, proposes an entirely inorganic 

 genetic system based on cation substitutions in clays. The major idea 



