Could TRAPPIST-1e and nearby rocky exoplanets realistically be dominated by microbial life rather than complex lifeforms?

The low-light argument may overextend Earth’s history into a different stellar environment. TRAPPIST-1e’s atmospheric chemistry could make ozone and oxidation develop more efficiently than on Earth, potentially enabling oxygenic respiration sooner. Pre-oxygen photosynthetic ecosystems also offer routes to substantial biological activity without modern-Earth oxygen levels.

• A 2026 coupled climate-photochemical model finds that ozone forms more efficiently on TRAPPIST-1e, potentially allowing a Great Oxidation Event up to 1 billion years earlier than Earth’s.
• That model finds oxygen levels could eventually enable oxygenic respiration and animal development, challenging a permanently microbial scenario.
• Pre-oxygen photosynthesizing life could generate atmospheric biosignatures before an Earth-like oxygen atmosphere exists.
• The 0.9% PAR estimate and very long biological timescales depend on assumptions linking oxygen production and evolutionary progress to photon availability; the source identifies the linear assumption as problematic.

Featured sourceDearth of Photosynthetically Active Radiation Suggests No Complex Life on Late M-Star Exoplanetsarxiv.org4 sourcesView sources