24 



Phanerozoic 



Precombrian 



WIDESPREAD 

 STROMATOLITES 



STEEPROCK LAKE 

 STROMATOLITES 



BULAWAYAN 

 STROMATOLITES 



OLDEST 



SEDIMENTARY 



ROCKS (GREENLAND) 



AGE 

 (x10 6 yrs.) 



re ■ 



|§6p 



~^<& < 



^1000 



^^\ 



7^1500 



^^ 



1^2000 

 > 



? 



--2500H 



i 



DIVERSE 

 MICROBIOTAS 



FORMATION 

 OF EARTH 



- '3000 {-I 



6&\ O 

 i 



O 

 i 



o 

 - 3500 - 



- 4000 - 



4500 - 1 



} 



SWAZILAND 

 "MICROFOSSILS" 



Figure III-l.— A summary chart showing the known geological distribution of 

 Precombrian fossil microorganisms (micro fossils) and stromatolites. Photo 

 courtesy J. W. Schopf 



