Evolution of Earth-like extrasolar planetary atmospheres: Assessing the atmospheres and biospheres of early Earth analog planets with a coupled atmosphere biogeochemical model

TL;DR

This study uses a novel coupled atmosphere-biogeochemistry model to analyze early Earth's atmospheric evolution, revealing complex oxidation pathways and implications for detecting biosignatures on exoplanets.

Contribution

It introduces the first quantitative analysis of catalytic cycles governing O$_2$ during Earth's GOE using a new coupled model with geological constraints.

Findings

Oxidation pathways are crucial in O$_2$ destruction.

Most O$_2$ in the upper atmosphere is formed abiotically.

Multiple atmospheric states can result from similar biospheric productivity.

Abstract

Understanding the evolution of Earth and potentially habitable Earth-like worlds is essential to fathom our origin in the Universe. The search for Earth-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of Earth as a reference for Earth-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on early Earth. The Great Oxidation Event (GOE) in Earth's history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O$_2$ concentrations are fixed to values inferred by geological evidence. Applying a unique tool, ours is the first quantitative analysis of catalytic cycles that governed O$_2$ in early Earth's atmosphere near the GOE. Complicated oxidation pathways play a key role in destroying O$_2$, whereas in the upper atmosphere, most O$_2$ is formed abiotically via CO$_2$ photolysis. The O$_2$ bistability found by Goldblatt et al. (2006) is not observed in our calculations likely due to our detailed CH$_4$ oxidation scheme. We calculate increased CH$_4$ with increasing O$_2$ during the GOE. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity (NPP) of the biosphere that produces O$_2$ is unique. Mixing, CH$_4$ fluxes, ocean solubility, and mantle/crust properties strongly affect NPP and surface O$_2$ fluxes. Regarding exoplanets, different "states" of O$_2$ could exist for similar biomass output. Strong geological activity could lead to false negatives for life.