Stromatolites represent lithified, layered formations that serve as tangible evidence of intricate interactions between microbial consortia and their surrounding habitats.
Hand sample of Dresser Formation stromatolite with domical topography (arrowed). Image credit: Hickman-Lewis et al., doi: 10.1130/G50390.1.
The most ancient morphological signatures of life on our planet frequently engender considerable debate, attributed to both the propensity of abiogenic mechanisms to generate superficially similar structures and the advanced alteration or metamorphism these microfossil specimens often undergo.
Historically, stromatolites have been regarded as pivotal macrofossils for the detection of life within ancient sedimentary strata; however, the biogenic provenance of archaic stromatolites has been subject to recurrent skepticism.
In a recent investigative endeavor, geoscientists affiliated with the Natural History Museum in London, along with other institutions, meticulously examined stromatolites dating back 3.48 billion years, originating from the Dresser Formation in Western Australia.
Employing a suite of advanced analytical techniques, including optical and electron microscopy, elemental geochemistry, Raman spectroscopy, and both laboratory- and synchrotron-based tomography, they successfully identified a multitude of characteristics unequivocally indicative of a biological genesis.
“Beyond conducting laboratory-based tomography on the 3D macrostructure of the stromatolites, we succeeded in achieving unprecedented sub-micron pixel and voxel resolutions for the imaging of Precambrian stromatolite microstructures through the utilization of phase contrast imaging at the SYRMEP beamline within the Elettra Synchrotron in Trieste, Italy,” the researchers articulated.
“This technological advancement facilitated the discernment of asymmetrical layer morphologies, interstitial voids resulting from the outgassing of decomposing organic matter, and columnar, vertically oriented structures interpreted as microbial palisade arrangements, a well-recognized biomarker for photosynthetic activity.”
“The stromatolites of the Dresser Formation have primarily undergone replacement by hematite owing to recent weathering processes,” they stated.
“While this transformation precludes the feasibility of organic geochemical analyses, such a mineralogical composition holds substantial significance for initiatives focused on the search for extraterrestrial life, particularly on Mars.”
“Surface sedimentary rocks on Mars have been subjected to analogous pervasive oxidation and are predominantly composed of iron oxides within their upper superficial layers, extending from centimeters to meters in depth.”
“Consequently, the stromatolites of the Dresser Formation may represent uniquely pertinent geological materials to elucidate a precise mode of biosignature preservation anticipated on the Martian surface.”
“As NASA’s Perseverance rover continues its comprehensive exploration of Jezero Crater, our efforts should be directed toward seeking morphological manifestations of life analogous to those identified within the Dresser Formation, and simultaneously preparing for sophisticated multi-technique analyses upon the eventual return of Martian samples to Earth.”
This groundbreaking research is comprehensively detailed in a published paper in the esteemed journal Geology.
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K. Hickman-Lewis et al. Advanced two- and three-dimensional insights into Earth’s oldest stromatolites (ca. 3.5 Ga): Prospects for the search for life on Mars. Geology, published online November 4, 2022; doi: 10.1130/G50390.1
