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Sustained wet–dry cycling on early Mars


The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet these are rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet–dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet–dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet–dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian–Hesperian transition (3.8–3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

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Fig. 1: In situ observations of polygonal ridges.
Fig. 2: Bedrock enrichments in Ca-sulfate and Mg-sulfate.
Fig. 3: Formation model for sulfate-enriched polygonal ridges.
Fig. 4: Mars’s potential for prebiotic record.

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Data availability

All data are available in the NASA Planetary Data System ( Geoscience Node in the Mars Science Laboratory directory ( or Supplementary Information.


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We thank A. Vasavada and A. Fraeman for discussions; and T. Goudge and J. Bishop for the comments and review. The data used are available in the NASA Planetary Data System Geoscience Node in the Mars Science Laboratory directory ( This project was supported in the United States by NASA’s Mars Exploration Program and in France is conducted under the authority of CNES. Mastcam mosaics were processed by the Mastcam team at Malin Space Science Systems. E.S.K. funding by NASA grant 80NSSC22K0731. L.M.T. funding as a Mars Science Laboratory team member is provided by the CSA.

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Authors and Affiliations



W.R. and G.D. equally led the writing of the paper. W.R., G.D., B.C.C., J.S., L.C.K., L.M.T., P.J.G., P.-Y.M. and J.L. contributed to methodology, investigation and data processing. O.G. and N.L.L. are the leads of the ChemCam instrument investigation. J.S. and E.S.K. provided significant contributions to the writing and reviewing of the paper. All co-authors provided helpful comments and inputs to the paper.

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Correspondence to W. Rapin.

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Nature thanks Janice Bishop and Timothy Goudge for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Context of observations in Gale crater, Mars.

Stratigraphic context (left) of the lower portion of Mount Sharp and map (right) showing Curiosity rover traverse (white) on the High Resolution Imaging Science Experiment (HiRISE) base map overlaid with Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) S-index, which tracks sulfates (shaded yellow). Red rectangle shows the location of close-up map and detailed stratigraphy (Extended Data Fig. 3b).

Extended Data Fig. 2 Larger color image of bedrock with polygonal ridges for context.

MastCam image (mcam100270) and close-ups (a,b and c) with rectangle locations of close-up view from Fig. 1. Close-ups (b,c) show bedrock 10 to 20 meters away where regularly spaced ridges and nodules can be observed supporting lateral extension of the same polygonal pattern although camera resolution prevents detailed geometrical analysis at this distance.

Extended Data Fig. 3 Local stratigraphic context of the examined section.

Close-up map of the examined sections along the rover traverse with location of the observed polygonal pattern (red circles) and associated geochemical measurements (red triangle and diamond, see Figs. 2, 3) (a); as well as general stratigraphic column for context with detailed log facies for East (Extended Data Fig. 9), Medium (Extended Data Fig. 10), and West (Extended Data Fig. 11) sections (b). Other locations with possible polygonal ridges as incipient or altered variants are annotated in Extended Data Fig. 12. The approximate distance of 200 m and 220 m between the adjacent sections centers is annotated on top (b). Facies are drawn based on available images from Mastcam M34/M100, MAHLI and ChemCam RMI. Nodular features within bedrock interpreted as chemical deposits are highlighted in red, whereas physical sedimentary structures are shown in blue. Sedimentary structures were rarely observed and the host rock of chemical deposits was mostly smooth and featureless. Geochemical data from polygonal ridges are represented with triangle (a and b). Location of ChemCam LIBS observations on bedrock are shown in the “CCAM obs.” column with a red cross where points analyzed chemical deposits and blue dot for host rock. Locations of APXS and MAHLI observations are also highlighted the same way, with a cross for chemical deposits and circle for host bedrock.

Extended Data Fig. 4 Polygonal ridges pattern analysis.

Top view of bedrock from sol 3154 generated using Onsight, with circles representing marked polygon sizes (blue) and junctions (yellow dots) connected to well-expressed (solid lines) and uncertain ridges (dashed lines) forming the pattern mapped on image (a). Red contour represents the area covered on Fig. 1e, and white rectangles areas for polygon size statistics (Supplementary information Table 1). Top view with extended context shows the area of analysis along with the location of closeups where polygonal ridges are observed in the distance (b). Elevation change is indicated by 1 m contour lines (yellow) to estimate the thickness of the observable strata from this location. Distribution of junction angles for well-expressed ridges only (solid red) and all ridges (dashed red) with gaussian fit (c). Distribution of polygon sizes and fit with Poisson probability distribution (d), see Supplementary information Table 1.

Extended Data Fig. 5 Flux of impacts on Mars through time.

Curves representing the impact rate chronology on Mars based on cumulative density of craters with D>1 km per unit area (a). This model is based on the equation from the crater chronology49,50 giving the cumulative number of craters larger than 1 km as N(1) = 5.44 × 10−14 [exp(6.93 T) − 1] + 8.38 × 10−4 T. The derivative of this function gives the flux of impact craters larger than 1 km over time (b) is given by the equation: N’(1) = 3.77 × 10−13 [exp(6.93 T) − 1] + 8.38 × 10−4 T. This curve presents a strong decrease in intensity of cratering with time which can be used as a proxy for extra-terrestrial material accretion with time. The link between the flux of impact craters of a given size and the accretion flux of the planet is then shown as a gradient bar (c) that is represented on Fig. 4 in the main text.

Extended Data Fig. 6 APXS data bedrock and diagenetic features.

CaO (a) and MgO (b) versus SO3 content for bedrock and diagenetic features in the investigated section. Resistant nodules, forming collectively nodular bedrock, show MgO and SO3 enrichment. The data only includes relatively clean, dust-free targets. List of target names for bedrock: Gourdon, Bardou_DRT, Ribagnac_DRT, Chenaud_DRT, Monpazier, Plaisance_DRT, Monsec_DRT. For veins/coating: Terrasson_Lavilledieu, Festalemps_DRT, Quinsac, Biras, Pezuls. For resistant bedrock: Gardonne_DRT, Simeyrols, Rouffignac, Bosset, Bosset_offset, Nabirat, Sarlande, Salagnac, Le_Bugue.

Extended Data Fig. 7 ChemCam images of fine-grained host bedrock.

The bedrock matrix typically composed of a light-colored smooth-textured mudstone.

Extended Data Fig. 8 ChemCam images of nodular bedrock.

Salt-bearing concretions are widespread and abundant in the examined section.

Extended Data Fig. 9 Stratigraphic log of East section.

Lumped nodules organized in polygonal ridges (dotted lines) on bedrock block (a, sol 3137 Montaut). Lumped nodules forming possible incipient ridges (dotted lines) on bedrock (b, sol 3137 Montignac). Irregular nodules forming possible incipient or altered ridges (dotted lines) observed within nodular bedrock (c, sol 3117 drive_direction). Laminated bedrock with variably coalescent nodular texture (d, sol 3119 allas_les_mines). Aligned, variably coalescent micro-nodules within laminar bedded facies (e, sol 3112 garreloup).

Extended Data Fig. 10 Stratigraphic log of Medium section.

Bedrock with evenly distributed dendritic nodules (a, sol 3147 workspace). Close-up image of a dendritic nodule showing jagged, multifaceted, multi-centimeter texture (b, MAHLI target Nabirat 25 cm standoff). Incipient polygonal ridges (dotted lines) on bedrock (c, sol 3139 workspace). Dendritic nodules (d, MastCam on Vayres).

Extended Data Fig. 11 Stratigraphic log of West section.

Partially coalescent nodules and laminar bedded facies (a, sol 3170 Organized_nodules). Nodular bedrock and laminar bedded facies adjascent to smooth or laminated bedrock at Pontours location (b, sol 3163 drill_area_context). Large, polymorphic vacuolar nodules (c, sol 3161 workspace). Coalescent nodules aligned in planar beds (d, sol 3158 diagenetic_transition). Incipient polygonal ridges (dotted lines) on bedrock (e, sol 3151 workspace).

Extended Data Fig. 12 Polygonal pattern as incipient or altered variants.

Details of images of other locations with possible polygonal ridges (dotted lines) from Extended Data Figs. 911 with markings (left) and without (right), see corresponding figures for context.

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This file contains Supplementary Tables 1–3.

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Rapin, W., Dromart, G., Clark, B.C. et al. Sustained wet–dry cycling on early Mars. Nature 620, 299–302 (2023).

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