CONTENTS VII 



Reefs of algal limestone in the Sahara 89 



Optimistic outlook 92 



Chapter VIII. the environment 94 



Weathering of rocks 94 



Minerals unstable in present weathering 95 



Minerals stable under anoxygenic atmosphere .... 96 



Studies by Rankama: detritus of granites 97 



Studies by Ramdohr: gold-uranium reefs 98 



Sands with pyrites, pitchblende and other minerals ... 99 



Age of sediments formed under anoxygenic atmosphere . 109 



Studies by Lepp and Goldich: iron formations 109 



Sediments formed under oxygenic atmosphere: the red beds 1 1 1 



Provisional dating of transition between the two atmospheres 1 13 

 Type of geological evidence drawn from fossils and from 



the environment 114 



Chapter IX. miscellaneous geological considerations . . 115 



General 115 



The importance of clays 116 



The importance of quartz 117 



Geochemical inventories 118 



Uniformity of surface temperature of the earth . . . . 120 



Glasshouse effect of the atmosphere 122 



The dangers of comparative biochemistry 124 



Chapter X. the origin of life and its later evolution . . 126 



Evolution and paleontology 126 



Seven assumptions 127 



Possibility of multiple biogenesis 129 



Chapter XL conclusions 131 



What we know 131 



What we shall never know 134 



What further research may teach us 135 



Closing remark 135 



references 137 



INDEX 141 



