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The oldest stromatolites on Earth and the search for life on Mars

The oldest stromatolites on Earth and the search for life on Mars

The oldest stromatolites on Earth and the search for life on Mars

Hand sample of a Dresser Formation stromatolite, showing a complex layered structure formed by hematite, barite, and quartz, and a domed upper surface (dome arrow). Credit: Keyron Hickman-Lewis and colleagues

The earliest morphological traces of life on Earth are often highly controversial, both because non-biological processes can produce relatively similar structures and because such fossils have often undergone advanced alteration and metamorphism.

Stromatolites, layered organo-sedimentary structures reflecting the complex interplay between microbial communities and their environment, have long been considered key macrofossils for uncovering ancient life sedimentary rocks; however, the biological origin of ancient stromatolites has often been criticized.

Article published on Friday in the magazine Geology uses a range of advanced two-dimensional and three-dimensional analytical techniques to determine the biological provenance of Earth’s oldest stromatolites from the 3.48-billion-year-old Dresser Formation, Pilbara, Western Australia.

The oldest stromatolites on Earth and the search for life on Mars

Optical photomicrograph (left) and EDX map (right) showing primary and replacement mineralogy in undulating beds of Dresser Formation stromatolites. Credit: Keyron Hickman-Lewis and colleagues

Although these stromatolites are subjected to severe diagenesis and weathering and do not preserve organic materials, the team led by dr. Keyron Hickman-Lewis from the Natural History Museum in London used optical and electron microscopyelemental geochemistry, Raman spectroscopy and laboratory and synchrotron tomography to identify numerous features that indicate a biological origin.

In addition to performing laboratory tomography of 3D stromatolitic macrostructure, the team was able to achieve the first submicron pixel and voxel sizes for imaging the Precambrian stromatolite microstructures by phase contrast imaging using the SYRMEP beamline at the Elettra Synchrotron, Trieste, Italy. This enabled the identification of patchy bed morphologies, voids resulting from degassing of decaying organic materials, and vertical pillar-like structures interpreted as microbial palisade structure, a common indicator of phototrophic growth.

The oldest stromatolites on Earth and the search for life on Mars

Three-dimensional representation of the microstructure of stromatolites, which allows visualization of the distribution of phases in the structure of stromatolites. Credit: Keyron Hickman-Lewis and colleagues

Dresser Formation stromatolites are mostly replaced by hematite (iron oxide) due to recent weather conditions. Although this makes organic geochemical analyzes impossible, this composition is highly relevant to the search for life on Mars.

Sedimentary rocks on the Martian surface have undergone similar comprehensive oxidation and also contain mainly iron oxides in their upper centimeters to meters. In this sense, Dresser Formation stromatolites may be uniquely relevant materials to inform us about the precise style of biosignature preservation expected on Mars.

As the Mars 2020 Perseverance rover continues its exploration of Lake Crater, we should look for morphological expressions of life that resemble those identified in the Dresser Formation and prepare for advanced multi-technique analyzes when samples from Mars eventually return to Earth.

More information:
K. Hickman-Lewis et al, Advanced two- and three-dimensional insight into Earth’s oldest stromatolites (ca. 3.5 Ga): Prospects for the search for life on Mars, Geology (2022). DOI: 10.1130/G50390.1

Citation: Earth’s oldest stromatolites and the search for life on Mars (2022, November 7) Retrieved November 8, 2022, from https://phys.org/news/2022-11-earth-oldest-stromatolites-life-mars.html

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