Earth’s oldest stromatolites and the search for life on Mars

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 are often subject to advanced changes and metamorphoses.

Stromatolites, layered organo-sedimentary structures due to complex interactions between microbial communities and their environment, have long been considered the most important macrofossils for detecting life in ancient times sedimentary rock; however, the biological origin of ancient stromatolites has often been criticized.

An article that appeared in the magazine on Friday Geology uses a range of advanced two- and three-dimensional analytical techniques to establish the biological origin of the oldest stromatolites on Earth from the 3.48-billion-year-old Dresser Formation, Pilbara, Western Australia.

Although these stromatolites have undergone severe diagenesis and weathering and do not retain organic materials, a team led by Dr. Keyron Hickman-Lewis of the Natural History Museum, London, optical and electron microscopyelemental geochemistry, Raman spectroscopy, and laboratory and synchrotron-based tomography to identify numerous features indicative of 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 Precambrian imaging stromatolite microstructures via phase contrast imaging using the SYRMEP beamline at the Elettra Synchrotron, Trieste, Italy. This allowed the identification of non-uniform layer morphologies, voids created by the outgassing of decaying organic materials, and pillar-like vertical structures interpreted as microbial palisade structure, a common indicator of phototrophic growth.

The stromatolites of the Dresser Formation have been largely replaced by hematite (iron oxide) due to recent weathering. While this makes organic geochemical analysis impossible, this composition is highly relevant to the search for life on Mars.

Sedimentary rocks on the surface of Mars are subject to similar pervasive oxidation and also contain mainly iron oxides in their upper centimeters to meters. In this regard, the Dresser Formation stromatolites may be uniquely relevant materials to inform us of a precise style of biosignature conservation expected on Mars.

As the Mars 2020 Perseverance rover continues its exploration of Jezero Crater, we must look for morphological expressions of life similar to those identified in the Dresser Formation and prepare for advanced multi-technical analysis when Mars samples eventually reach the Earth. be returned to earth.