32 



in fixing these dates, but it does seem possible that both chemical 

 and isotopic investigations might be of substantial use. Kerogen 

 analyses might follow an approach already highly successful in other 

 fields of geochemistry and concentrate on determinations of stable 

 isotopes of the elements present. It seems likely, for example, that 

 any shift in the mode of primary production of polyatomic carbon 

 molecular skeletons — chains and rings and the like — would have 

 been accompanied by some shift in the ratio of light to heavy carbon 

 isotopes within the reduced organic matter. 



Whatever else they might do, kerogen analyses must deal with 

 the fact that differences observed between specimens are as likely to 

 be due to postdepositional effects as to differences in the original 

 communities. The mineralogy, as it pertains to the origin and evolu- 

 tion of the rocks, and the structural geology of a given rock unit 

 must be considered in addition to its organic geochemistry if this is 

 to be done adequately. Such investigations are becoming more fre- 

 quent, with many investigators realizing that the methods they 

 choose should be designed both to decode the chemical message 

 which might describe the original community and to assess the state 

 of preservation of that message. 



It seems appropriate in the study of microfossils with single 

 structural morphology, such as most of those found in the Archean, 

 to seek chemical-supporting data to establish their biological origin. 

 Combined electron microprobe-scanning, electron microscope sys- 

 tems can now detect C, N, O, and P in micron-sized objects within 

 reasonable limits of error. Micropaleontologists, using, e.g., micro- 

 probe techniques capable of detecting elements with atomic numbers 

 as low as carbon, may be able to resolve details of the original 

 organisms that left their remains. 



Just the same, Precambrian paleobiology has now made notable 

 advances. These include the certain great antiquity of now uncon- 

 tested stromatolites, the wonderful Ediacaran fauna, the Bitter 

 Springs, Gunflint, Transvaal, Belcher Island, and Fig Tree microfos- 

 sils, and the oldest "North Pole" finds from W. Australia. Some of 

 these deposits contain an abundance of well-preserved forms, e.g., 

 Gunflint, Bitter Springs; others contain only relatively few forms, 

 most of which are broken "debris," e.g., Transvaal. What is note- 

 worthy is that these micropaleontological and organic geochemical 

 findings can be related in some degree to living analogues. 



