Global Abiotic Sulfur Cycling on Earth-like Terrestrial Planets

TL;DR

This paper introduces an open-source model to simulate Earth's abiotic sulfur cycle over deep time, highlighting differences in sulfur distribution that could inform studies of habitable exoplanets.

Contribution

It provides a novel dynamical model for abiotic sulfur fluxes and concentrations, excluding biological influences, to understand planetary sulfur geochemistry.

Findings

Marine sediment sulfate content is two orders of magnitude higher without life.

Marine sediment sulfide content is four orders of magnitude lower without life.

Model helps predict sulfur cycling on potentially habitable exoplanets.

Abstract

Sulfur is a redox active element that may have helped mediate an electron flow that kickstarted life and which presently is an essential element for all life on Earth. Despite current uncertainties in global sulfur fluxes, modeling sulfur's abiotic cycling through Earth's deep history is important for understanding the impact of a planet wide biosphere on sulfur geochemical cycling and availability and vice versa. We present here an open-source, dynamical box model for estimating global sulfur fluxes and concentrations among surface and deep Earth reservoirs over Earth history, allowing tracking and estimation of the sulfur distribution in planetary reservoirs over deep time in the absence of life. While the main model presented here does not take into account the abrupt evolution of redox-shunting biosynthetic pathways such as oxygenic photosynthesis, we also modeled the abiotic sulfur cycle before and after a Great Oxidation Event-like transition on Earth-like planets. Our results suggest a considerably distinct chemical makeup of sulfur content in marine sediments in the absence of life on an Earth-like planet, leading to a marine sediment sulfate content two orders of magnitude larger than on present-day Earth and a marine sediment sulfide content 4 orders of magnitude lower than on present day Earth, attributable to the lack of microbial sulfur metabolism. This model could be useful for understanding sulfur cycling on potentially habitable exoplanets.