Power and Biological Potential

Habitability, biomass abundance, growth rates, and rates of evolution are constrained by the availability of biologically accessible energy through time -- power. It is well understood that life requires energy not only to grow, but also to support standing biomass without new growth. Quantifying this “maintenance energy” requirement is critical for understanding the biological potential of low energy systems, including many systems of astrobiological interest, but field- and culture-based estimates differ by as much as three orders of magnitude. Here, we evaluate and compare these estimates to environmental energy supply in two examples: methanogenic metabolism in serpentinizing systems and a hypothetical “thermotrophic” metabolism. In both cases, evaluation of the power budget introduces constraint and resolution beyond that provided by evaluation of Gibbs energy change for metabolic reactions.