Environmental structuring of early biosphere evolution: spatial decoupling of metabolic innovation and ecological expansion in cyanobacteria

The emergence of cyanobacteria fundamentally transformed Earth’s surface environment by enabling oxygenic photosynthesis, ultimately leading to atmospheric oxygenation and the rise of complex life. Although the biochemical mechanisms underlying this metabolism are well understood, the environmental pathway from localized metabolic activity to global ecological dominance remains unclear. Here, we propose a conceptual framework in which metabolic emergence and ecological expansion were spatially decoupled. We suggest that long-term stabilization of oxygenic photosynthesis preferentially occurred under ultraviolet-attenuated conditions, whereas large-scale proliferation required warm, high-productivity environments capable of sustaining elevated metabolic flux. These phases were linked by iron redox chemistry, which acted as a geochemical valve coupling local oxygen production to broader ecological expansion. Within this framework, early carbon isotopic signatures lacking morphological fossils reflect spatially restricted metabolic activity, whereas stromatolites represent a later phase of sustained ecosystem engineering. This perspective reframes the Great Oxidation Event as a consequence of ecosystem scaling rather than metabolic innovation alone. Our model provides a generalizable framework for interpreting early biosphere evolution and may inform the search for life on other planets.