Geologic data on atmospheric history
Attention is focussed on the possible existence of an anoxygenic, primeval atmosphere and on the history of atmospheric O2 and CO2. 
 
For this purpose, geologic data can be divided into those on fossil remains, on biogenic deposits formed by early life, on “chemicofossils”, and on deposits formed by exogenic geologic processes. Only the latter, mainly through the processes of weathering and sedimentation, give any indication of the nature of the contemporaneous atmosphere. 
 
A tentative schematic diagram of the history of atmospheric O2 and CO2 is presented in Fig. 1.