33 



The pursuit of kerogen investigation, together with related bio- 

 logical and geological studies, seems very likely to fulfill its promise. 

 Organic geochemists now appear to have a good chance to make sig- 

 nificant contributions, less to the blunt question "when did life 

 arise?" than to the much more detailed set of questions dealing with 

 the biochemical natures of the ancient communities once they are 

 disclosed to the searching paleontological eye. 



THE RECORD IN LIVING FORMS 



While the paleontologist studies the fossils that the old organ- 

 isms left in the rocks, the biochemist would like to study the biologi- 

 cal processes in those earliest organisms. The descendants of those 

 ancient organisms are alive today, and they, with their molecular 

 traditions from the past, can be the subject of the biochemist's 

 investigations. Some of these traces exist in a form much changed 

 from the original, while others appear to have been handed down to 

 generation after generation, practically unchanged. One important 

 simple tenet of evolutionary theory is this: If several organisms are 

 found to share a certain trait, that trait was most likely inherited 

 from a common ancestor rather than evolved independently on 

 several separate occasions. But certain important features are now 

 shared in identical form by every organism extant. For instance, all 

 life contains one set of amino acids, the building blocks of proteins, 

 and one set of nucleotides, the building blocks of nucleic acids (ribo- 

 nucleic acid (RNA) and deoryribonucleic acid (DNA), the genetic 

 material). The main features of the complex system which serves to 

 pass genetic information from one generation to the next are shared 

 by all organisms. That is a clean example of what biochemistry can 

 tell us about early common ancestors of all life: They contained 

 nucleic acids, spelling out a genetic code for proteins, and they passed 

 these down to all life forms present today. The random reorderings 

 of amino acids and nucleotides observed in functionally related 

 polymers must have evolved over the eons through various shuffling 

 and mutational events. Locked in the arrangement of the monomers 

 in various polymers in the cells of organisms is a coded record of the 

 evolution of these organisms. The key to reading this record lies in 



