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Long-lasting habitable periods in Gale crater constrained by glauconitic clays


In situ investigations by the Mars Science Laboratory Curiosity rover have confirmed the presence of an ancient lake that existed in Gale crater for up to 10 million years. The lake was filled with sediments that eventually converted to a compacted sandstone. However, it remains unclear whether the infilling of the lake was the result of background sedimentation processes or represents punctual flooding events in a largely isolated lake. Here, we used the X-ray diffraction data obtained with the Chemistry and Mineralogy instrument onboard the Curiosity rover to characterize the degree of disorder of clay minerals in the Murray formation at Gale crater. Our analysis shows that they are structurally and compositionally related to glauconitic clays, which are a sensitive proxy of quiescent conditions in liquid bodies for extended periods of time. Such results provide evidence of long periods of extremely low sedimentation in an ancient brackish lake on Mars, the signature of an aqueous regime with slow evaporation at low temperatures. More in general, the identification of lacustrine glauconitic clays on Mars provides a key parameter in the characterization of aqueous Martian palaeoenvironments that may once have harboured life.

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Fig. 1: Intensities corresponding to clay minerals after extraction from the bulk diffraction pattern with the Le Bail method.
Fig. 2: Stacking faults in clay minerals.
Fig. 3: Experimental and calculated patterns of the glauconitic clays.
Fig. 4: Possible sequence of precipitation of glauconitic clays in the Murray formation and main steps of the physico-chemical evolution of the water column.

Data availability

Source data are provided with this paper. All data used in this study are freely available from the Planetary Data System database ( The data supporting the findings of this study are available within the paper, in the Supplementary Information file or from the corresponding author upon reasonable request.


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We thank T. Bristow for excellent feedback that notably improved the clarity of an early version of this manuscript. We also thank the Mars Science Laboratory team members for their dedication to generating the Planetary Data System database, especially to the CheMin Team. E.L.-A. was supported by the program GRC-ED431C 2017/55 (Xunta de Galicia) granted to the XM-1 group of the Universidade de Vigo, and A.G.F. by the Project ‘MarsFirstWater’, European Research Council Consolidator grant no. 818602.

Author information

Authors and Affiliations



E.L.-A. and L.G.-D. conceived the original idea and analysed and interpreted the data. C.G.-L. and A.G.F. contributed to the interpretation of the results and gave technical support and conceptual advice. E.L.-A. and L.G.-D. drafted the manuscript and designed the figures. C.G.-L., A.G.F., J.L.B. and E.B.R. contributed preliminary discussions defining the direction of the project. A.G.F., J.L.B. and E.B.R. provided insights on current results of orbital and in situ measurements on Mars. All authors provided critical feedback and helped shape the research, analysis and manuscript.

Corresponding author

Correspondence to Elisabeth Losa-Adams.

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The authors declare no competing interests.

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Peer review information Nature Astronomy thanks Adrián López-Quirós and Peter Ryan for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Bulk XRD patterns of drill samples acquired by the CheMin instrument in the Murray formation (Sebina, Quela, and Marimba).

The marked peaks as Kapton represent the signal emitted by the window of the sample holder. The figure also indicates the reflections corresponding to (001) and (02 l) lattice planes of clay minerals.

Extended Data Fig. 2 XRD intensity profiles of ‘nascent’ glauconite with 0 wt. % K2O and ‘intermediate’ glauconite with 4.5 wt. % K2O.

The XRD patterns were calculated with the Rietveld method by using the same structural model (atomic coordinates, lattice parameters, and space group) and identical profile parameters (shape of intensities and scales). No multilayers are considered in the model. It is observable the difference in integrated intensities when the occupation factor of K+ is varied.

Extended Data Fig. 3 Rietveld fits of MB sample using different compositional models for the refinement of the clay mineral phase.

a, Using ‘nascent’ glauconite, without K and low iron content, similar to a ferric collapsed smectite, (b) using glauconite with a 4.5 wt. % K2O and high iron content in the structure. The wt. % values resulting from the Rietveld fits are as follows: a) 28.2 wt. % of ‘nascent’ glauconite, and b) 17.6 wt. % of glauconite (wt. % values are referred to the sum of crystalline phases, excluding the background). χ2 of the refinements are marked at the bottom of the plots. The graphs show the observed intensity, I (obs.), marked with stars, the calculated intensity, I (cal.) (solid line), and the difference between both intensities, I (obs.) - I (cal.) (solid gray line). Bragg’s positions are marked as bars.

Extended Data Fig. 4 Rietveld refinement of the XRD data of SB, QL, and MB.

Le bail method was used to obtain the profile of the clay minerals. Bars (I) indicate the Bragg positions of the different mineral phases in the samples. From top to bottom: Glauconitic clay, andesine, hematite, anhydrite, bassanite, gypsum, sanidine, forsterite, diopside, jarosite, and tridymite. χ2 of the refinements are marked at the bottom of the plots. The graphs show the observed intensity, I (obs.), marked with stars, the calculated intensity, I (cal.) (solid black line), and the difference between both intensities, I (obs.) - I (cal.) (solid golden line).

Extended Data Fig. 5 Comparison between XRD patterns of minerals affected for rotational disorder and the resulting in MB from the Le Bail method.

(a), Top and bottom, XRD patterns (red) of rotationally disordered non-ferric illites showing the broadening effect of n·120° rotations over the set of reflections verifying the condition k = 3n. The upper pattern corresponds to a cis-vacant structure (cv-1Md), as is marked by the diagnostic (111) peak. The bottom pattern corresponds to a trans-vacant disposition (tv-1Md), marked by the absence of (111) peak. In both cases, low iron content is reflected by the diagnostic presence of (002). The blue curve shows the intensity’s profile of MB resulting from the Le Bail method. Here, the absence of (002) corresponds to a clay mineral with high-iron content. The ratio (111) < (−112) is indicative of a tv/cv interstratification, a typical feature of interstratified G-S. The extensive broadening of the set of k = 3n reflections, not affecting the (001) peak is indicative of n·120° rotational disorder. All these features are diagnostic of a mixed layer G-S evolution. (b), Broadening of k = 3n reflections due to random stratification of layers or when rotational disorder of n 60° kind dominates. Upper curve (Blue) correspond to data from MB and the bottom curve (red) correspond to a 4.5 wt. % K2O glauconite, without rotational disorder. The intensities are in arbitrary units.

Extended Data Fig. 6 Redox stratification and location of glauconitic facies into the Gale Crater Lake according with the Goldschmidt sedimentation sequence.

The sedimentary facies displayed to the left are similar to those reported by Hurowitz et al.36 in the Gale crater. These facies correspond to the Goldschmidt sequence14, characterized by the presence of glauconite between coarse/fine-grained detrital sediments and carbonates (on Earth) and saline deposits.

Extended Data Fig. 7 HRTEM lattice fringe image illustrating the glauconitization pathway.

(a), Orientation relations between mature glauconite and ferric smectite. The central glauconite sheets consist of a defect-free regular sequence of 10 Å layers; whereas, the collapsed Fe-smectite show anastomosing d-spacings with abundance of edge dislocations. Both minerals are disposed in a subparallel way, with clear discontinuities between glauconite and smectite layers. The amorphization features of smectite around the border of grains (areas enclosed as circles) suggest a solvent-mediated growth of glauconite at expenses of smectite, in a process similar to Ostwald ripening. There are also appreciable dissolution features and d-spacings of 0.45 nm corresponding to (020) not perpendicular to (001) indicative of rotation between layers. (b), Partially dissolved glauconite after attack by 1 M HCl for 24 h showing the amorphization of the structural framework of tetrahedral and octahedral sheets, although the 10 Å basal repeat is still observable. c) SAED diagram of natural glauconitic mineral showing rotational disorder in the a*b* section. Glauconite samples were obtained from the sediment-water interface at a depth of 200 m from the Galician continental shell (NW of Spain).

Extended Data Fig. 8 Geochemical modeling of the process of dissolution-precipitation between nontronite and glauconite.

The right panels show the trend of Fetot (Fe2+, Fe3+) and K+ along the process. The models were performed at 293 K (a) and b)) and at 273 K (c) and d)). Since the concentration of the solution depends on the initial temperature, the course of salinity is different through the same evaporative process.

Supplementary information

Supplementary Information

Supplementary Tables 1–7, Discussion and Note

Source data

Source Data Fig. 3

Le Bail and FAULTS data

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Losa-Adams, E., Gil-Lozano, C., Fairén, A.G. et al. Long-lasting habitable periods in Gale crater constrained by glauconitic clays. Nat Astron 5, 936–942 (2021).

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