Information-Thermodynamic Bounds on Planetary Biosphere Productivity and Their Observational Tests

TL;DR

This work derives a universal information–thermodynamic upper bound on planetary biosphere productivity by subtracting the minimal energy cost of heritable information processing from the planetary power budget. The bound links observable exoplanetary quantities (stellar irradiation, climate, disequilibria) with microscopic information-processing costs via Landauer-type limits and proofreading penalties, yielding a concrete relation: $\mathrm{NPP} \le \dfrac{\eta_{bio}}{\Delta G_{assim}}\big(P_{in}-P_{maint}-P_{info}^{(min)}\big)$. It identifies regimes where productivity is dominated by available energy (resource-limited) versus those where information-processing demands dominate (information-limited), and provides a self-consistent closure tying $\dot N_{copy}$ to $\mathrm{NPP}$. Earth serves as a calibration point showing the bound is loose under current conditions, while low-flux worlds (e.g., M-dwarf zones, subsurface oceans) can approach the information-limited regime, constraining the possible complexity of heritable information. The paper also outlines an observational retrieval framework to place physics-based upper limits on NPP and to test these limits against atmospheric and temporal data, offering a falsifiable avenue for assessing planetary biosignatures against fundamental thermodynamic constraints.

Abstract

The productivity of a planetary biosphere is limited by how its free-energy budget is partitioned between maintaining a habitable environment, driving metabolism, and processing heritable information. We derive an upper bound on net primary productivity (NPP) from non-equilibrium thermodynamics and information theory, given a planet's usable free-energy flux and a few coarse-grained biological parameters. The bound subtracts an irreducible power cost of heritable information processing -- set by global template-copying rates, copying fidelity, alphabet size, and proofreading work -- from the planetary power budget before converting the remainder into biomass. This yields an ``information-productivity trade-off'': at fixed planetary power, higher copying rates, lower error rates, larger alphabets, or more intensive proofreading all lower the ceiling on biomass production. Using conservative parameter choices, we show that Earth lies well below this ceiling, whereas low-flux environments such as M-dwarf habitable zones and subsurface ocean worlds can be driven into an information-limited regime where only modest combinations of productivity and heritable complexity are attainable. We outline how future exoplanet observations of stellar irradiation, climate, atmospheric disequilibria, and temporal variability could be used to place physics-based upper limits on NPP and compare them with independent productivity estimates.