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


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 model that incorporates 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 (hydrogen-rich) to oxidizing (oxygen-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 carbon dioxide 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 build-up of atmospheric oxygen, 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’s early climate and surface chemistry would have presented both challenges and opportunities for any emergent microbial life.

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Fig. 1: Observations versus atmospheric evolution model predictions over Mars’s history.
Fig. 2: Integrated duration of warm intervals as a function of hydrogen fluxes into the Martian atmosphere.
Fig. 3: Thermochemical sulfate reduction on Mars in the Noachian period.
Fig. 4: Manganese oxidation on Mars during a late-stage brief warming event.

Data availability

The input data to the model used to produce the plots in this paper are available on GitHub at, and, with the exception of the HITRAN data used by the line-by-line radiative–convective model and the one-dimensional regolith heating data, which are available on Zenodo at

Code availability

The stochastic atmospheric evolution model, along with other scripts to reproduce plots in the paper, is available open source on GitHub at The line-by-line radiative–convective model used to produce the climate parameterization (PCM_LBL) is available open source on GitHub at The regolith thermal evolution model is available open source on GitHub at The Geochemist’s Workbench is proprietary software available at


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R.W. thanks D. Johnston, K. Loftus, Y. Sekine and K. Zahnle for discussions. We thank N. Lanza for helpful comments on an earlier version of the manuscript. Funding: R.W. and M.B. acknowledge funding from NSF CAREER award AST-1847120 and NASA/VPL grant UWSC10439. J.H. acknowledges support from the Simons Collaboration on the Origin of Life.

Author information




R.W., A.H.K. and J.H. conceived the paper. M.B. performed the one-dimensional regolith heating calculations. K.S. performed the post-impact three-dimensional climate simulations. R.W. performed the rest of the modelling and wrote most of the manuscript. B.L.E. provided ideas and text on surface geochemical evolution, timing and the role of evaporitic versus thermochemical processes. J.W.H. provided input and background on planetary volcanism, impactor and fluvial/lacustrine processes, and geological evolution. All authors discussed the results and provided input on multiple draft versions of the manuscript.

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Correspondence to Robin Wordsworth.

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Peer review informationNature Geoscience thanks David Catling, Edwin Kite and Nicolas Mangold for their contribution to the peer review of this work. Primary Handling Editors: Tamara Goldin; Rebecca Neely

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Wordsworth, R., Knoll, A.H., Hurowitz, J. et al. A coupled model of episodic warming, oxidation and geochemical transitions on early Mars. Nat. Geosci. 14, 127–132 (2021).

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