Chapter XI 



CONCLUSIONS 



WHAT WE KNOW 



The factual conclusions from our study of the geological aspects of 

 the origin of life on earth have been summarized in Fig. 36. Fig. 35 

 is a companion figure, for comparison with Fig. 36. Fig. 35 is taken 

 from the American paleontologist and stratigrapher Raymond C. 

 Moore (1958) and shows what geology is normally interested in, 

 i.e. the study of the history of the earth, datable by the fossil record. 

 Detailed information of this kind practically begins at the base of 

 the Paleozoic, with the Cambrian system. Nine out of ten of the 

 phyla of the animal kingdom were already represented in the Cam- 

 brian system. Very little, on the other hand, is known about earlier 

 periods, and all ancestry lines during this time are dotted, with the 

 exception of that of the microbes. Moreover, at about 1200 my ago, 

 everything originates from nebulous beginnings. 



In Fig. 36 Moore's picture is re-drawn on another scale to em- 

 phasize those earlier periods of the history of the earth. From this 

 picture it follows immediately how relatively short the time since the 

 beginning of the Paleozoic is, when compared to the time life has 

 existed on earth. There are no nebulous beginnings around 1200 my 

 ago, but we have real fossils of some 1600 my ago, and even much 

 older indications of the presence of life on earth. 



Apart from the fossils and para-fossils, there are definite indications 

 that the earth had an anoxygenic atmosphere of reducing character, 

 certainly up to 2 billion years ago. Some of the indications we have 



Fig. 35. Evolution of life on earth, as schematized by R. C. Moore 

 (1958). Main divisions of plants and animals and their evolutionary 

 development in the course of time are shown. Times of some important 

 orogenetic periods in North America are posted at the left. 



