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The ancient rocks of the Pilbara region of Western Australia have been an important analogue site for the study of possible inhabited environments in the search for life on early Mars for over four decades. These rocks contain the oldest, most convincing evidence of life on Earth in the 3.48 billion-year-old (Ga) Dresser Formation, situated within a hydrothermally-charged volcanic caldera lake environment. Here, stromatolites occupied very shallow water to emergent environments, including active hot springs that locally concentrated boron. An older occurrence of coniform stromatolites within shallow marine carbonates of the 3.7 Ga rocks of the Isua Supracrustal Belt, West Greenland, are still under scientific investigation to determine their biogenicity, while metaturbidites from the same belt contain carbon isotopic values indicative of life.


Figure 1: Wrinkly laminated stratiform (foreground), and domal (background) stromatolites in surface outcrops of the 3.48 Ga Dresser Formation. Shallow water rippled sediment with crystal splays of evaporative aragonite immediately underlying these horizons, combined with lithostratigraphic and facies analyses, indicate microbial growth on the shoreline of a shallow evaporative caldera lake.



Figure 2: Centimetre-high, domal, sulfidized stromatolites in drillcore through the 3.48 Ga Dresser Formation, Pilbara Craton. Note how these structures rise up from flat-laminated sulfidized sediment below and contain internal wrinkly laminations. Stromatolite growth was terminated by a high-energy event that buried them in coarse sand (green material between columns), prior to a return to abiological carbonate sediment accumulation.


Figure 3: Detailed elemental map view of a part of one of the Dresser Formation columnar sulfidized stromatolites, showing alternating enrichments of Ni and Zn in the As-rich pyrite matrix that dominates these structures. From Baumgartner et al. (2020c).

A review of the evidence for Paleo- to Neoarchean (3.7-2.5 billion-year-old (Ga)) life from the Pilbara Craton and unconformably overlying Fortescue Group of the Mount Bruce Supergroup show that it occupied a variety of habitats that range from land to sea, and into the subsurface, with shallow water environments by far the most common. The evidence for a flourishing biosphere on early Earth is found in the form of macroscopic fossil stromatolites, microfossils, and elemental concentrations and isotopic values of sulfur and carbon.

These results demonstrate that even in early Earth history, life occupied a variety of habitats and had diversified into, and flourished within, a range of different environments early in Earth history. Although identifying metabolisms of this early life are challenging due to a lack of diagnostic biosignatures arising from high metamorphic heat flow in these ancient rocks, examination of elemental concentrations and isotopic values from early life samples indicate a variety of metabolisms were likely present, including a range of sulfur metabolisms and probable anoxygenic photosynthesis in the oldest rocks. Evidence for oxygenic photosynthesis is found from 2.7 Ga rocks of this study area.


Figure 4: Large columnar stromatolites of the 2.72 Ga Tumbiana Formation, Fortescue Group, Western Australia, which flourished in shallow water evaporative lakes and may have been dominated by oxygenic phototrophic bacteria. From Van Kranendonk et al. (2021).


Additional studies from the contemporaneous Barberton Greenstone Belt of southern Africa show a similar richness of life and diversity of inhabited environments, again dominated by shallow water conditions.

Further Reading

Baumgartner, R., Van Kranendonk, M.J., Wacey, D., Fiorentini, M., Saunders, M., Caruso, S., Pagès, A., Homann, M., Guagliardo, P. (2019): Nano-porous pyrite and organic matter in 3.5 billion-year-old stromatolites record primordial life. Geology, v. 47, p. 1039-1043.


Baumgartner, R., Caruso, S., Fiorentini, M.L., Van Kranendonk, M.J., Martin, L., Jeon, H., Wacey, D., Pagès, A. (2020a): Sulfidization of 3.48 billion–year–old stromatolites of the Dresser Formation, Pilbara Craton: Constraints from in-situ sulfur isotope analysis of pyrite. Chemical Geology, 538: 119488.


Baumgartner, R.J., Van Kranendonk, M.J., Fiorentini, M.L., Pages, A., Wacey, D., Kong, C., Saunders, M., Ryan, C. (2020b): Formation of micro-spherulitic barite in association with organic matter within sulfidized stromatolites of the 3.48 billion–year–old Dresser Formation, Pilbara Craton. Geobiology 18, p. 415-425. doi: 10.1111/gbi.12392


Baumgartner, R.J., Van Kranendonk, M.J., Pagès, A., Fiorentini, M.L., Wacey, D., Ryan, C. (2020c): Accumulation of transition metals and metalloids in sulfidized stromatolites of the 3.48 billion–year–old Dresser Formation, Pilbara Craton. Precambrian Research, 337, 105534; doi: 10.1016/j.precamres.2019.105534.


Buick, R. (1992): The antiquity of oxygenic photosynthesis: Evidence from stromatolites

in sulphate-deficient Archaean lakes. Science 255, 74–77.


Djokic, T., Campbell, K.A., Van Kranendonk, M.J. (2021): A reconstructed subaerial hot spring field in the ~3.5 billion-year-old Dresser Formation, North Pole Dome, Pilbara Craton, Western Australia. Astrobiology 21(1), 1-38. DOI: 10.1089/ast.2019.2072.

Djokic, T., Bolhar, R., Brengman, L.A., Havig, J., Van Kranendonk, M.J. (2024): Trace elements (REE+Y) record marine, subaerial, and hydrothermal conditions influencing stromatolitic settings in the c. 3.5 Ga Dresser Formation, Pilbara Craton, Western Australia. Chemical Geology, 121865.

Flannery, D.T., Walter, M.R. (2011): Archean tufted microbial mats and the Great Oxidation Event: new insights into an ancient problem. Australian Journal of Earth Sciences 59, 1-11.


Flannery, D.T., Summons, R.E., Walter, M.R. (2018a): Archean Lakes as Analogues for Habitable Martian Paleoenvironments. In: N. Cabrol & E. Grin (eds) From Habitability to Life on Mars. Elsevier, 127-152.


Flannery, D.T., Allwood, A.C., Sumons, R.E., Williford, K.H., Abbey, W., Matys, E.D., Ferralis, N. (2018b): Spatially-resolved isotopic study of carbon trapped in ~3.43 Ga Strelley Pool Formation stromatolites. Geochimica et Cosmochimica Acta 223, 21-35.


Djokic, T., Van Kranendonk, M.J., Campbell, K.A., Walter, M.R., Ward, C.R. (2017): Earliest signs of life on land preserved in c. 3.5 Ga hot spring deposits. Nature Communications 8: 15263.


Nutman, A.P., Bennett, V.C., Friend, C.R.L., Van Kranendonk, M.J., Chivas, A. (2016): Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature 537, 535-538. DOI 10.1038/nature19355


Nutman, A.P., Friend, C.R.L., Chivas, A., Van Kranendonk, M.J., Bennett, V.C., Rothacker, L. (2019): Cross-examining Earth’s oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ~3700 Ma sedimentary rocks. Precambrian Research 331, 105347. DOI:10.1016/j.precamres.2019.105347


Nutman, A.P., Bennett, V.C., Friend, C.R.L., Van Kranendonk, M.J. (2021): In support of rare relict ~3700 Ma stromatolites from Isua (Greenland). Earth and Planetary Science Letters 562, 116850.


Rosing, M.T. (1999): 13C-depleted carbon microparticles in >3700 Ma sea-floor sedimentary rocks from West Greenland. Science 283, 674-676.


Shen, Y., Buick, R., Canfield, D.E. (2001): Isotopic evidence for microbial sulphate reduction in the early Archaean era. Nature 410, 77-81.


Shen, Y., Farquhar, J., Masterson, A., Kaufman, A.J., Buick, R. (2009): Evaluating the role of microbial sulfate reduction in the early Archean using quadruple isotope systematics. Earth and Planetary Science Letters 279, 383–391.


Sugitani, K., Lepot, K., Nagaoka, T., Mimura, K., Van Kranendonk, M., Oehler, D.Z., Walter, M.R. (2010): Biogenicity of morphologically diverse carbonaceous microstructures from the ca. 3400 Ma Strelley Pool Formation, in the Pilbara Craton, Western Australia. Astrobiology 10, 899-920.


Sugitani, K., Mimura, K., Nagaoka, T., Lepot, K., Takeuchi, M. (2013): Microfossil assemblage from the 3400Ma Strelley Pool Formation in the Pilbara Craton, Western Australia: Results from a new locality. Precambrian Research 226, 59-74.


Sugitani, K., Mimura, K., Takeuchi, M., Lepot, K., Ito, S., Javaux, E.J. (2015a): Early evolution of large micro-organisms with cytological complexity revealed by microanalyses of 3.4 Ga organic-walled microfossils. Geobiology 13, 507-521.


Sugitani, K., Mimura, K., Takeuchi, M., Yamaguchi, T., Suzuki, K., Senda, R., Asahara, Y., Van Kranendonk, M.J. (2015b): A Paleoarchean coastal hydrothermal field inhabited by diverse microbial communities: the Strelley Pool Formation, Pilbara Craton, Western Australia. Geobiology 13, 522-545. DOI 10.1111/gbi.12150


Sugitani, K., Kohama, T., Mimura, K., Takeuchi, M., Senda, R., Morimoto, H. (2018): Speciation of Paleoarchean life demonstrated by analysis of the morphological variation of lenticular microfossils from the Pilbara Craton, Australia. Astrobiology 18, 1057-1070.


Van Kranendonk, M.J., Philippot, P., Lepot, K., Bodorkos, S., Pirajno, F. (2008): Geological setting of Earth’s oldest fossils in the c. 3.5 Ga Dresser Formation, Pilbara Craton, Western Australia. Precambrian Research 167, 93-124. DOI 10.1016/j.precamres.2008.07.003.


Van Kranendonk, M.J., Djokic, T., Baumgartner, R., Bontognali, T., Sugitani, K., Kiyokawa, S., Walter, M.R. (2021): Life analogue sites for Mars from early Earth: Diverse habitats from the Pilbara Craton and Mount Bruce Supergroup, Western Australia. In: R.J. Soare, S.J. Conway, D.Z. Oehler, and J.-P. Williams (eds), Mars Geological Enigmas: From the Late Noachian Epoch to the Present Day, pp. 357-403, Elsevier Inc. USA, 554p.


Wacey, D., McLoughlin, N., Whitehouse, M.J., and Kilburn, M.R. (2010): Two coexisting sulfur metabolisms in a ca. 3400 Ma sandstone. Geology 38, 1115-1118.


Wacey, D., Saunders, M., Cliff, J.B., Kilburn, M.R., Kong, C., Barley, M.E., Brasier, M. (2014): Geochemistry and nano-structure of a putative ∼3,240 million-year-old black smoker biota, Sulfur Springs Group, Western Australia. Precambrian Research 249, 1-12.

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