干旱区生态环境知识资源中心

The distinctive features of biota at successive stages of its development in the Proterozoic and Early Paleozoic are analyzed. Based on this analysis the minimum possible and most probable oxygen contents of the atmosphere at each of these stages are determined. It is shown that Proterozoic organisms with the higher level of organization than the background ones first appeared in oxygen oases and that later, when the same mean oxygen content was achieved across the entire water area because of an increase in atmospheric oxygen, these organisms spread widely with an explosive increase in morphological and taxonomic diversity.