The role of carbonates in the evolution of early Martian oceans

Abstract

ABSTRACT. Central to the question of life on Mars is whether there has been liquid water on the martian surface and how the planet could have evolved from possible initial warm and wet conditions to the cold and dry present state. Virtually all models for this climatic evolution rely strongly on the removal of an initial thick carbon dioxide atmosphere by precipitation of carbonate minerals from surface waters that may have been quite similar to those of Hadean Eon Earth's oceans. In order for this to occur, a hydrologic cycle would be necessary in which chemical weathering of silicate rocks consumes CO 2 that precipitates as carbonates in an acidic martian ocean which probably had a very high alkalinity. The consumption of atmospheric CO 2 by this process would result in a gradual decrease of the atmospheric greenhouse influence and cooling of the climate.Once the surface of Mars became cold enough so that freezing conditions prevailed, the hydrologic cycle would largely cease, and the uptake of CO 2 by silicate rock weathering would greatly diminish. The alkalinity of the freezing seawater would probably be sufficient to result in the removal of all calcium as calcium carbonate. Some magnesium and sodium would also likely be removed as carbonates as well. The removal of these cations as carbonates has a major influence on the final temperature at which liquid brines would be able to persist on the surface of Mars. During the period of freezing, the oceans would act as a source of CO 2 rather than a sink, further slowing the rate of climate change on Mars.

Europa's Crust and Ocean: Origin, Composition, and the Prospects for Life

“…The FREZCHEM 5 model (modified after Spencer et al 1990 by Marion and Grant 1994, Mironenko et al 1997, with modifications including addition of carbonate minerals and improved parameterizations of sulfates to high ionic strengths) was used without carbonate to compute the thermal evolution of chondritic brines. An earlier version of this computational tool was used to investigate the chemical evolution by freezing of Earth's seawater and a hypothetical martian ocean (Morse and Marion 1999). The FREZCHEM models select the compositions of the solutions and solid phases that minimize the Gibbs free energy of the system.…”

Modeling aluminum–silicon chemistries and application to Australian acidic playa lakes as analogues for Mars

“…Earth analogues for Meridiani Planum surface geochemistries include: (1) acid mine drainages (AMD) (Fernandez-Remolar et al, 2003Bishop et al, 2004), (2) Antarctic deserts (Wierzchos and Ascaso, 2002;Bishop et al, 2003;Kreslavsky and Head, 2008), and (3) acidic saline lakes (Benison and LaClair, 2003;Benison and Bowen, 2006;Benison et al, 2007;Bowen and Benison, 2008). Potential geochemistries of Meridiani Planum have also been explored using laboratory studies (Banin et al, 1997;Tosca et al, 2004;Golden et al, 2005) and modeling (Schaefer 1990(Schaefer , 1993Morse and Marion, 1999;King et al, 2004;Marion and Kargel, 2008;Marion et al, 2008b). In a recent paper, Benison and Bowen (2006) made a strong case for why WA acidic, saline lakes are especially sound as analogues for the Burns formation in the Meridiani Planum region of Mars.…”

The composition and evolution of primordial solutions on Mars, with application to other planetary bodies

“…Because these models invoke a separate fluid source for S, this has allowed authors to "decouple" the S salts from the other salts, and instead model S-free brines on the surface of Mars (e.g., Cl-fluids in Knauth and Burt, 2002; HCO 3 ϩCO 3 -fluids in Morse and Marion, 1999). These simplified systems, while instructive, may not provide accurate predictions of solution evolution, because on Earth the S-species cannot operate in isolation from other soluble species such as Cl -, HCO 3 -, and CO 3 2-(e.g., Table 1) in either high-temperature systems (Krauskopf and Bird, 1995) or low-temperature evaporite systems (Hardie and Eugster, 1970).…”