Hand sample of Dresser Formation stromatolite, revealing an intricate layered structure formed of quartz, hematite, and barite, and a domed upper surface area (dome arrow). Credit: Keyron Hickman-Lewis and coworkers
Advanced 2D-3D insights into Earths earliest stromatolites.
The oldest morphological traces of life in the world are in some cases very questionable, both since non-biological processes may generate relatively similar structures and since such fossils have often gone through advanced alteration and metamorphism.
Stromatolites, layered organo-sedimentary structures that show complex interactions between microbial neighborhoods and their environment, have actually long been considered as important macrofossils for detecting life in ancient sedimentary rocks; nevertheless, the biological origin of ancient stromatolites has been extensively disputed. A paper just recently released in the journal Geology of the Geological Society of America integrates a variety of innovative 2- and three-dimensional analytical techniques to identify the biological origins of Earths earliest stromatolites from the 3.48-billion-year-old Dresser Formation in Western Australia.
Three-dimensional rendering of stromatolite microstructure, allowing the distribution of stages throughout the structure of the stromatolites to be envisioned. Credit: Keyron Hickman-Lewis and coworkers
Regardless of the truth that these stromatolites have undergone extreme diagenesis and weathering and do not consist of any organic materials, a group led by Dr. Keyron Hickman-Lewis of the Natural History Museum, London, has utilized optical and electron microscopy, essential geochemistry, Raman spectroscopy, and lab- and synchrotron-based tomography to determine a number of attributes suggestive of a biological origin.
In addition to carrying out lab tomography of 3D stromatolitic macrostructure, the team was able to achieve the first sub-micron pixel and voxel sizes for imaging of Precambrian stromatolite microstructures by means of phase contrast imaging utilizing the SYRMEP beamline at the Elettra Synchrotron, Trieste, Italy. This enabled the identification of non-uniform layer morphologies, space areas developing from the degassing of decaying organic products, and pillar-like vertical structures analyzed as microbial palisade structures, a typical indicator of phototrophic growth.
Optical photomicrograph (left) and EDX map (right) revealing main and replacement mineralogy in undulatory laminations of the Dresser Formation stromatolites. Credit: Keyron Hickman-Lewis and coworkers
The Dresser Formation stromatolites have actually been mostly replaced by hematite (iron oxide) due to recent weathering. While this renders natural geochemical analyses impossible, this structure is highly appropriate for the search for life on Mars.
Sedimentary rocks at the surface of Mars have undergone similar prevalent oxidation and likewise consist of mainly iron oxides in their upper centimeters to meters. In this regard, the Dresser Formation stromatolites may be uniquely relevant materials to notify us of a precise design of biosignature preservation anticipated on Mars. As the Mars 2020 Perseverance rover continues its exploration of the Jezero crater, we ought to look for morphological expressions of life looking like those determined in the Dresser Formation and prepare for innovative multi-technique analyses when Martian samples are eventually returned to Earth.
Reference: “Advanced two- and three-dimensional insights into Earths earliest stromatolites (ca. 3.5 Ga): Prospects for the search for life on Mars” by K. Hickman-Lewis, B. Cavalazzi, K. Giannoukos, L. DAmico, S. Vrbaski, G. Saccomano, D. Dreossi, G. Tromba, F. Foucher, W. Brownscombe, C.L. Smith and F. Westall, 4 November 2022, Geology.DOI: 10.1130/ G50390.1.
Sedimentary rocks at the surface of Mars have actually been subjected to similar prevalent oxidation and also consist of mostly iron oxides in their upper centimeters to meters. In this regard, the Dresser Formation stromatolites may be distinctively relevant materials to inform us of an accurate design of biosignature conservation anticipated on Mars. As the Mars 2020 Perseverance rover continues its expedition of the Jezero crater, we must search for morphological expressions of life resembling those identified in the Dresser Formation and prepare for advanced multi-technique analyses when Martian samples are ultimately returned to Earth.
