CONCLUSIONS 



133 



to "-' y 





Fig. 36. Schematic history of hfe on earth. 1. Biogenic lime secretions 

 from South Africa, described by MacGregor. 2a. Earliest true fossils, 

 described from Canada by Tyler and Barghoorn. 2b. Anoxygenic Blind 

 River deposits, described from Canada by Ramdohr. 3. Collenia type 

 algal reefs from Africa, described by Gravelle and Lelubre. 4. Non- 

 oxidized rocks from Finland, described by Rankama. 5. Anoxygenic 

 Dominion Reef deposits from South Africa, described by Ramdohr. 

 7. Anoxygenic iron formations, described from Canada and Montana, 

 by Lepp and Goldich. 8. Approximate age of earliest red beds. For 

 geographical location of numbers 1 to 7, compare Fig. 15. 



