Several lines of evidence have recently reinforced the hypothesis that an ocean existed on early Mars1,2,3,4,5,6,7. Carbonates are accordingly expected to have formed from oceanic sedimentation of carbon dioxide from the ancient martian atmosphere7,8. But spectral imaging of the martian surface has revealed the presence of only a small amount of carbonate, widely distributed in the martian dust9. Here we examine the feasibility of carbonate synthesis in ancient martian oceans using aqueous equilibrium calculations. We show that partial pressures of atmospheric carbon dioxide in the range 0.8–4 bar, in the presence of up to 13.5 mM sulphate and 0.8 mM iron in sea water8, result in an acidic oceanic environment with a pH of less than 6.2. This precludes the formation of siderite, usually expected to be the first major carbonate mineral to precipitate8. We conclude that extensive interaction between an atmosphere dominated by carbon dioxide and a lasting sulphate- and iron-enriched acidic ocean on early Mars is a plausible explanation for the observed absence of carbonates.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Clifford, S. M. & Parker, T. J. The evolution of the martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains. Icarus 154, 40–79 (2001)
Phillips, R. J. et al. Ancient geodynamics and global-scale hydrology on Mars. Science 291, 2587–2591 (2001)
Dohm, J. M. et al. Ancient drainage basin of the Tharsis region, Mars: Potential source for outflow channel systems and putative oceans or paleolakes. J. Geophys. Res. 106, 32943–32958 (2001)
Craddock, R. A. & Howard, A. D. The case for rainfall on a warm, wet early Mars. J. Geophys. Res. 107, doi:10.1029/2001JE001505 (2002)
Fairén, A. G. et al. Episodic flood inundations of the northern plains of Mars. Icarus 165, 53–67 (2003)
Malin, M. C. & Edgett, K. S. Evidence for persistent flow and aqueous sedimentation on early Mars. Science 302, 1931–1934 (2003)
Moore, J. M. Blueberry fields for ever. Nature 428, 711–712 (2004)
Catling, D. C. A chemical model for evaporites on early Mars: Possible sedimentary tracers of the early climate and implications for exploration. J. Geophys. Res. 104, 16453–16469 (1999)
Bandfield, J. L., Glotch, T. D. & Christensen, P. R. Spectroscopic identification of carbonate minerals in the martian dust. Science 301, 1084–1087 (2003)
Carr, M. H. & Head, J. W. Oceans on Mars: An assessment of the observational evidence and possible fate. J. Geophys. Res. 108, doi:10.1029/2002JE001963 (2003)
Kirkland, L. E., Herr, K. C. & Adams, P. M. Infrared stealthy surfaces: Why TES and THEMIS may miss some substantial mineral deposits on Mars and implications for remote sensing of planetary surfaces. J. Geophys. Res. 108, doi:10.1029/2003JE002105 (2003)
Huguenin, R. L. J. The formation of goethite and hydrated clay minerals on Mars. J. Geophys. Res. 79, 3895–3905 (1974)
Mukhin, L. M., Koscheev, A. P., Dikov, Yu. P., Huth, J. & Wänke, H. Experimental simulations of the photo-decomposition of carbonates and sulphates on Mars. Nature 379, 141–143 (1996)
Clark, B. C. On the non-observability of carbonates on Mars. 5th Mars Conf. Abstr. 6214 (Lunar and Planetary Institute, Houston, Texas, 1999).
Baker, V. R. Water and the Martian landscape. Nature 412, 228–236 (2001)
Head, J. W. III, Kreslavsky, M. A. & Pratt, S. Northern lowlands of Mars: Evidence for wide-spread volcanic flooding and tectonic deformation in the Hesperian Period. J. Geophys. Res. 107, doi:10.1029/2000JE001445 (2002)
Bhattacharyya, A. & Friedman, G. M. Modern Carbonate Environments (Hutchinson Ross, Stroudsburg, Pennsylvania, 1983)
Brain, D. A. & Jakosky, B. M. Atmospheric loss since the onset of the martian geologic record: Combined role of impact erosion and sputtering. J. Geophys. Res. 103, 22689–22694 (1998)
Squyres, S. W. & Kasting, J. F. Early Mars: How warm and how wet? Science 265, 744–749 (1994)
Forget, F. & Pierrehumbert, R. T. Warming early Mars with carbon dioxide clouds that scatter infrared radiation. Science 278, 1273–1276 (1997)
Melosh, H. J. & Vickery, A. M. Impact erosion of the primordial atmosphere of Mars. Nature 338, 487–489 (1989)
Barley, M. E., Pickard, A. L. & Sylvester, P. J. Emplacement of a large igneous province as possible cause of banded iron formation 2.45 billion years ago. Nature 385, 55–58 (1997)
Russell, M. J. & Hall, A. J. The emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front. J. Geol. Soc. 154, 377–402 (1997)
Holland, H. D. The oceans: A possible source of iron in iron-formations. Econ. Geol. 68, 1169–1172 (1973)
Zuber, M. T. The crust and mantle of Mars. Nature 412, 220–227 (2001)
Schaefer, M. W. Aqueous geochemistry on early Mars. Geochim. Cosmochim. Acta 57, 4619–4625 (1993)
Burns, R. G. Ferric sulfates on Mars. J. Geophys. Res. 92, 570–574 (1987)
Fernández-Remolar, D. et al. The Tinto river, an extreme acidic environment under control of iron, as an analog of the Terra Meridiani hematite site of Mars. Planet. Space Sci. 52, 239–248 (2003)
Johnson, J. W., Oelkers, E. H. & Helgeson, H. C. SUPCRT92: A software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bars and 0° to 1000 °C. (Earth Sciences Department, Lawrence Livermore Laboratory, 1991).
Bruland, K. W. in Chemical Oceanography 8 (eds Riley, J. P. & Chester, R.) 157–220 (Academic, London, 1983)
Special acknowledgements to the MER team, as their compelling evidence probing the acidity of martian palaeoenvironments was unfolded while our work was in progress, and resulted in adjustments in our model following our initial submitted draft. We also thank S. Clifford, I. Fairchild and J. Kasting for comments and suggestions that refined and focused this paper.
The authors declare that they have no competing financial interests.
About this article
Frontiers in Microbiology (2019)
Annual Review of Earth and Planetary Sciences (2019)
Frontiers in Microbiology (2019)
Meteoritics & Planetary Science (2019)
Ore Geology Reviews (2019)