(ORDO NEWS) — The earliest morphological traces of life on Earth are often highly controversial because non-biological processes can produce relatively similar structures, and in addition, such fossils have often undergone significant alteration and metamorphism.
The paper, published in the journal Geology, uses a range of advanced 2D and 3D analytical techniques to establish the biological origin of Earth’s oldest stromatolites from the 3.48 billion year old Dresser Formation found in the Pilbara region of Western Australia.
Although these stromatolites had undergone severe diagenesis and weathering and retained no organic material, a team led by Dr. Keiron Hickman-Lewis of the Natural History Museum, London, used optical and electron microscopy, elemental geochemistry, Raman spectroscopy, and laboratory and synchrotron tomography to reveal the characteristics, pointing to a biological origin.
The team was able to achieve the first submicron pixel and voxel sizes to visualize Precambrian stromatolite microstructures using phase contrast imaging using the SYRMEP beam channel at the Elettra synchrotron.
This made it possible to identify heterogeneous layer morphology, void spaces resulting from degassing of decaying organic materials, and columnar vertical structures interpreted as a microbial palisade structure, a common indicator of phototrophic growth.
The stromatolites of the Dresser Formation have been mostly replaced by hematite (iron oxide) due to recent weathering.
Although this makes organic geochemical analysis impossible, this composition is of great importance in the search for life on Mars.
Sedimentary rocks on the Martian surface have undergone similar widespread oxidation and also contain mainly iron oxides in the upper layers.
As the Perseverance rover continues its exploration of the Lake crater, we should look for morphological manifestations of life similar to those found in the Dresser Formation and prepare for advanced multi-method analysis when the Martian samples are eventually brought back to Earth.
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