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Searching for biosignatures in sedimentary rocks from early Earth and Mars


The recognition of past habitable environments on Mars has increased the urgency to understand biosignature preservation in and characterize analogues of these environments on Earth. In this Review, we examine the detection and interpretation of potential biosignatures preserved in deposits rich in carbonates, silica and clay. Many of the earliest chemical, textural and morphological evidence of life on Earth are found in carbonates and carbonate-hosted phases. Early diagenetic chert within carbonate deposits can exceptionally preserve microbial body fossils, and clay minerals that form in ultramafic terrains can protect organic matter. On Mars, similar deposits older than 3.5 billion years could contain biosignatures or remnants of prebiotic processes that have long been erased from Earth. Terrestrial analogues for the deposition of magnesium carbonate minerals in Jezero crater, Mars, present patterns that can guide the collection of samples with the highest astrobiological potential by the Perseverance rover. Continued characterization of terrestrial analogue sites and rigorous examination of the processes that impact the preservation of isotopic signals, organic compounds, and microbial textures and fossils will advance the interpretation of Martian deposits.

Key points

  • Sedimentary deposits on Mars that are older than 3.5 billion years could contain biosignatures or remnants of prebiotic processes that have long been erased from Earth.

  • Diverse terrains and minerals in and around Jezero crater record an ancient, previously unexplored, surface environment that contains deltaic sediments rich in clay minerals produced during the weathering of ultramafic rocks, widespread carbonate minerals and patches of hydrated silica.

  • Studies of biosignatures from early Earth and processes that preserve microbial fossils and organic matter in environments will inform the identification and collection of samples in Jezero crater, Mars.

  • Precipitated hydrated magnesium carbonate minerals in lakes on Earth can preserve textural biosignatures, microbial fossils and organic matter, and are good targets for exploration on Mars.

  • Early diagenetic hydrated silica and Fe/Mg smectite minerals within ultramafic terrains have a high potential to preserve organic compounds and biosignatures.

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Fig. 1: Landing site of the Perseverance rover and mineral distribution in Jezero crater, Mars.
Fig. 2: Biogenic textures in Archaean stromatolites and modern terrestrial microbialites.
Fig. 3: Exceptionally preserved Archaean biogenic textures and fossils of filamentous organisms in chert.
Fig. 4: Gas-related textures.
Fig. 5: Biogenic textures in modern terrestrial microbialites.
Fig. 6: Radial-fibrous and palisade textures containing elongated crystals of calcite, aragonite and silica sinter.
Fig. 7: Deposition of magnesium carbonate minerals in ultramafic terrains.


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The authors thank the Simons Foundation Collaboration on the Origins of Life (grants to T.B. and J.P.G.) and the NASA Mars 2020 programme.

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T.B. wrote and edited the article. K.R.M., J.G. and J.P.G. provided comments and figures and contributed to the editing.

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Correspondence to Tanja Bosak.

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Microbial mats

Laminated, mm-thick or cm-thick layered organic or organosedimentary structures formed by a benthic microbial community.


Laminated sedimentary structures that are attached to the substrate and grow away from a point or plane.


Time period in the early history of Mars, likely more than 3.6 billion years ago, characterized by impacts and the presence of liquid water at the surface.


Organosedimentary deposits resulting from a benthic microbial community trapping and binding sediment and/or acting as the locus of mineral precipitation.


Concentrically layered and rounded grains less than 2 mm in diameter.


A form of titanium dioxide.


mm-Scale and cm-scale flat-rimmed areas that form owing to the precipitation of minerals in thin films.


A macroscopic multilobed structure with lobes that radiate from the same point.


Long, narrow mineralized strings with long axes aligned in the direction of the flow.


Microbialites that are not clearly laminated, instead containing clotted and sometimes porous textures.


Concentrically layered and rounded grains more than 2 mm in diameter.


Spheroidal grains that lack distinct layering.

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Bosak, T., Moore, K.R., Gong, J. et al. Searching for biosignatures in sedimentary rocks from early Earth and Mars. Nat Rev Earth Environ 2, 490–506 (2021).

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