Implications of Abiotic Oxygen Buildup for Earth-like Complex Life

Abstract

One of the chief paradoxes of molecular oxygen (O${}_2$) is that it is an essential requirement for multicellular eukaryotes on Earth while simultaneously posing a threat to their survival via the formation of reactive oxygen species. In this paper, the constraints imposed by O${}_2$ on Earth-like complex life are invoked to explore whether worlds with abiotic O${}_2$ inventories can harbor such organisms. By taking the major O${}_2$ sources and sinks of Earth-like planets into account using a simple model, it is suggested that worlds that receive time-averaged X-ray and extreme ultraviolet fluxes that are $\gtrsim 10$ times higher than Earth might not be capable of hosting complex lifeforms because the photolysis of molecules such as water may lead to significant O${}_2$ buildup. Methods for testing this hypothesis by searching for anticorrelations between biosignatures and indicators of abiotic O${}_2$ atmospheres are described. In the event, however, that life successfully adapts to high-oxygen environments, these worlds could permit the evolution of large and complex organisms.

Published in The Astronomical Journal; 9 pages; 2 figures

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