EVOLUTION 



303 



in millions of years. The percentage following this figure is the 

 percentage of the whole of geological time. The bracketed 

 figures give time durations of the periods. The table is based 

 on a total of 1,800 millions of years of geological time. 



It will be noted from Table 1 that prior to the Cambrian 

 period only the more primitive forms of life have been found. 

 Thus the sedimentary rock of the Azoic era is entirely without 

 fossils. During the Archeozoic and Proterozoic eras life was 

 beginning, but in all a total of something over 1,000 millions of 

 years passed before the record shows the existence of inverte- 



