Mars

Hematite Is A Mineralogical Marker Of Ancient Climate Change On Mars

by Keith CowingJuly 9, 2026July 9, 2026

Proposed conceptual model of hematite formation and evolution in Gale crater. (A) Stratigraphic column from Fig. 1A showing boundaries between the Murray, Carolyn Shoemaker, and Mirador formations (black lines). (B) Left, ferrihydrite formation from dissolved Fe(III) and deposition. The vertical arrow indicates a transition from wet (blue) to dry (dark gray) surface conditions, reflecting a shift from lacustrine deposition in the Murray and Carolyn Shoemaker formations to groundwater-dominated settings in the Mirador formation. Middle, early diagenesis produced small hematite crystallites and goethite from ferrihydrite. Right, late diagenesis. The vertical arrow shows decreasing diagenetic temperatures from warmer conditions (red), favoring goethite-to-hematite transformations and hematite coarsening in the Murray formation, to colder conditions (gray) that inhibit further alteration. The horizontal arrow (top) indicates cooling surface temperatures from ≥0°C to present-day conditions. Dotted horizontal lines are boundaries between formations. Red arrows indicate warm conditions. Shapes indicate hematite, ferrihydrite, goethite, and groundwater (see legend). -- Science

[Science via PubMed] The ancient climate of Mars changed from warm to cold surface conditions. This climate transition is demonstrated by geomorphological evidence but lacks suitable mineralogical indicators.

We investigated the crystallographic properties of hematite (iron oxide) in Gale crater measured by the Curiosity rover and compared them with laboratory experiments. Hematite crystallite sizes are about 5 to 65 nm in the oldest sedimentary rocks investigated by the rover (the Murray formation) and less than 10 nm in the younger overlying strata (the Mirador and Carolyn Shoemaker formations).

We attribute the larger crystallites in the Murray formation to postdepositional coarsening by groundwater in warm and wet conditions that persisted for several million years. Hematite with small crystallites co-occurs with goethite (iron oxyhydroxide) in the overlying layers, consistent with colder and water-limited conditions.

Hematite is a mineralogical marker of ancient climate change on Mars, Science via PubMed
Hematite is a mineralogical marker of ancient climate change on Mars, Science (open access)

Astrobiology, Astrogeology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp... More by Keith Cowing

Hematite Is A Mineralogical Marker Of Ancient Climate Change On Mars

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