Closure of Constraints in the Earth System: Biogeochemical Cycles and Planetary-Scale Biological Organisation

Alejandro Merlo 

The concept of closure of constraints has been developed as a characterization of the distinctive causal regime at work in biological systems. Its extension to ecological systems has been attempted but faces persistent difficulties regarding the individuation of ecosystems and the scope of functional ascription. Meanwhile, the question of the biological character of the Earth system (variously approached through the concepts of organism, autopoiesis, and self-regulation) remains open, and the available frameworks each illuminate certain aspects of the planetary system while leaving others unaddressed. In this paper, I argue that the closure-of-constraints framework provides an especially apt conceptual tool for articulating what is specifically biological about the organisation of the Earth system, and that the planetary scale may provide a more tractable domain for this framework than the ecosystem. The central claim is that organisational closure does not reside in any individual biogeochemical cycle (which are regularly but misleadingly used as examples of merely physical circularity) but in the organisation that the Earth’s biogeochemical cycles form together. Each cycle maintains flows and levels of distinct elements, but can only do so if the others are also functioning; together they sustain system-level properties that are simultaneously conditions and expressions of a determinate organisational regime. I illustrate this with the Quaternary period as an example of an evolved, stable organisational state. The paper contributes both to the ongoing debate on the applicability of closure of constraints to supra-organismal systems and to the broader question of the nature of the living Earth system.