Integrating Planetary Atmosphere, Interior, and Photosynthesis Models to Constrain Environmental Controls on the Evolution of Light-Harvesting Processes and Biosignature Production

Understanding the broad environmental context in which photosynthesis evolved is key to understanding its significant role in long-term biogeochemical cycles (carbon, in particular) operating in the wider Earth system. Duffy et al. (2023) developed an agnostic evolutionary model of photosynthetic light-harvesting processes. Given some environmental parameters this physics-based, machine learning algorithm ‘evolves’ efficient light-harvesting bioarchitectures. These parameters are the spectral irradiance of light, temperature, and the availability of chemical reductants.

However, this model does not yet couple photosynthetic organisms to the atmospheric and geophysical processes of the Earth, limiting its ability to develop our understanding of the role of the Earth's changing environment in the evolution of photosynthesis, as well as to predict broad biosphere characteristics and possible atmospheric biosignatures in the atmospheres of distant planets. Ecosystems powered by oxygenic and/or anoxygenic photosynthesis offer several remotely detectable atmospheric 'biosignatures', including a strong spectral signal (the ‘red ‘edge’) at the visible/NIR transition, as well as gaseous byproducts of both anoxygenic and oxygenic photosynthesis (O2, CH4, H2S etc.) that are emitted into the atmosphere. Should exoplanetary ecosystems driven by photosynthesis exist, these may be remotely detectable by spectroscopy using next-generation observatories.

This project will leverage existing models of varying complexity, including 1-D photochemical-climate, 2-D geophysical, and 3-D GCMs, that have been modified for comparative planetology (Rushby et al. 2018, 2020; Woodward et al. 2025) to provide more robust input into the evolutionary photosynthesis model, thereby improving constraints on the environmental controls affecting the emergence and evolution of light-harvesting processes.