A coupled model of episodic warming, oxidation and geochemical transitions on early Mars

Abstract

Reconciling the geology of Mars with models of atmospheric evolution remains a major challenge. Martian geology is characterized by past evidence for episodic surface liquid water, and geochemistry indicating a slow and intermittent transition from wetter to drier and more oxidizing surface conditions. Here we present a new model incorporating randomized injection of reducing greenhouse gases and oxidation due to hydrogen escape, to investigate the conditions responsible for these diverse observations. We find that Mars could have transitioned repeatedly from reducing (H2-rich) to oxidizing (O2-rich) atmospheric conditions in its early history. Our model predicts a generally cold early Mars, with mean annual temperatures below 240 K. If peak reducing gas release rates and background CO2 levels are high enough, it nonetheless exhibits episodic warm intervals sufficient to degrade crater walls, form valley networks and create other fluvial/lacustrine features. Our model also predicts transient buildup of atmospheric O2, which can help explain the occurrence of oxidized mineral species such as manganese oxides at Gale Crater. We suggest that the apparent Noachian--Hesperian transition from phyllosilicate deposition to sulfate deposition around 3.5 billion years ago can be explained as a combined outcome of increasing planetary oxidation, decreasing groundwater availability and a waning bolide impactor flux, which dramatically slowed the remobilization and thermochemical destruction of surface sulfates. Ultimately, rapid and repeated variations in Mars' early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life.

Published March 8 2021 in Nature Geoscience

References in corpus (8)

• Global modelling of the early Martian climate under a denser CO2 atmosphere: Water cycle and ice evolution
• Warming early Mars with CO2 and H2
• Outgassing History and Escape of the Martian Atmosphere and Water Inventory
• Evolution of Water Reservoirs on Mars: Constraints from Hydrogen Isotopes in Martian Meteorites
• Testing the Early Mars H2-CO2 Greenhouse Hypothesis with a 1-D Photochemical Model
• Anoxic Atmospheres on Mars Driven by Volcanism: Implications for Past Environments and Life
• A New Line-By-Line General Circulation Model for Simulations of Diverse Planetary Atmospheres: Initial Validation and Application to the Exoplanet GJ 1132b
• A Probabilistic Case For A Large Missing Carbon Sink On Mars After 3.5 Billion Years Ago

Cited by in corpus (2)

• 3-D Global modelling of the early martian climate under a dense CO2+H2 atmosphere and for a wide range of surface water inventories
• Multiple moist climate equilibrium states on arid rocky M-dwarf planets: A last-saturation tracer analysis