Spatial partitioning of environmental constraints in the early Earth biosphere evolution

Early Earth evolution is commonly interpreted through models that assume environmental constraints acted uniformly across the planet and were gradually relaxed over time, yet geological and geochemical evidence indicates a strongly heterogeneous Earth in which key constraints varied across space. Here, we propose a unifying conceptual framework in which major biospheric transitions arise from the spatial partitioning of environmental constraints rather than from globally uniform forcing. Within this framework, ultraviolet radiation defines spatial barriers to metabolic stabilization, metabolic flux imposes capacity constraints on biomass accumulation, and iron redox chemistry operates as a dynamic valve regulating ecological expansion through biogeochemical feedbacks. By explicitly linking spatial structure to the emergence and scaling of biological function, this perspective decouples metabolic innovation from ecological dominance and provides an alternative to trait-centered and globally averaged models, offering a new interpretation of the Great Oxidation Event as the outcome of spatially structured ecological expansion rather than a direct consequence of metabolic invention. More generally, this framework predicts that spatial heterogeneity in environmental constraints governs the timing, location, and extent of biological transitions, suggesting a general principle for the organization of biological processes across scales.