88 THE FOSSILS 



The important points of tiie Gunflint fossils are, first, that they 

 are real fossils, being structurally-preserved remains of organisms; 

 secondly, that remains are found of several quite different plants, 

 indicating the existence already at that time of a diversified, although 

 of course primitive, flora; and lastly, their great age, which is now 

 thought to be 1600 my. 



Thus far, to quote the 1954 paper of Tyler and Barghoorn, five 

 distinct organic forms have been recognized, four multicellular, and 

 one unicellular. Two of the former are related to algae and two 

 others to fungi. Their form is best seen from the accompanying 

 photographs (Figs. 20-23). Microbiologists who have studied the 

 original thin sections agree without the slightest hesitation that all 

 these are really fossilized remains of simple plants and microbes. 

 The amazing fact, to my mind, is that this is not only proof of the 

 existence of life at that time, but also of the high level of diversifica- 

 tion it had already attained. We are already far removed from the 

 beginning, when all life was still represented by microbes, because 

 there is already a definite variety of simple forms of higher plant 

 life. 



The age of these earliest fossils was not easily settled at first. In 

 1954 only helium measurements were available, not even from the 

 Gunflint formation itself in Ontario, but from magnetite of the 

 Negaunee iron formation in Michigan, which was correlated in a 

 rather loose way with the Gunflint, and thought to have a slightly 

 younger or about the same age. The helium datings, notoriously un- 

 trustworthy, ranged from 800 my to 1650 my, averaging 1300 my. 

 The plant fossils were found near the base of the Gunflint, however, 

 and consequently an age approaching 2 billion years was thought 

 likely. It is this figure which has since been repeated in the literature, 

 trying to make the 'oldest fossils' as old as possible. Later, as yet 

 unpublished rubidium — strontium determinations of the Gunflint iron 

 formation itself gave consistent absolute ages of 1600 my (Barghoorn, 

 in lit.), the figure which is provisionally accepted here. 



Apart from the absolute age of these earliest fossils, the question 

 of their environment is of importance. Did these primitive plants still 

 live under a pre-actualistic atmosphere, or did they already belong 

 to actual life, living under a normal oxygenic atmosphere? At the 

 present state of our knowledge this cannot be decided. As will be 



