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Final Report Summary - INACMA (Inorganic Nanoparticles in Archaean Carbonaceous Matter - a key to early life and palaeoenvironmental reconstructions)

The primary focus of the INACMa research project was the characterization of inorganic nanoparticles (IN) in ancient Archaean (3.5-3.2 billion year-old) carbonaceous material (CM) for deciphering crucial aspects of the nature of early life and its environmental context. IN have great potential as a biosignature and paleoenvironmental proxy when associated with fossil objects.
Rock samples from the Barberton greenstone belt in South Africa were obtained, prepared and routinely characterized in 2014 and 2015. This step was an essential milestone in the development of a digital catalogue of all the acquired results and for the reconstruction of lithological microfacies. Based on these results, in the following two years of the project, it was possible to select and further investigate the most promising samples containing features rich in carbonaceous material and of potential biological origin. These selected samples were investigated using in situ high-resolution analytical technics, in order to define the nature of their CM and related IN components. Through collaboration with national and international colleagues, and with two PhD students also involved in this project, the proponent has successfully developed a standard for sample preparation and analyses for the different in situ, high-resolution analytical techniques (from micron- to atomic-scale observation) used in this research.
In particular, the following was undertaken: 1) a combination of analytical techniques was required to characterize the CM; 2) specific experiments (at high-resolution) were designed to identify, measure and quantify heavy metals and IN content; 3) specific standards were manufactured for the calibration of sensitive instruments to measure organics and trace elements. This methodological approach has permitted us to define some significant biosignatures and keys for environmental reconstructions of the early Earth.
In the frame of the project, one of the PhD students has recently demonstrated that analyses of the Raman signals obtained from the study of the Archean carbonaceous matter, different CM precursors could be identified and could indicate – and may reflect – either different CM sources or different alteration chemistries from various microbial metabolic pathways. The other PhD project has demonstrated that as modern biological dependency on low concentrations elements may be a consequence of their enrichment in the early oceans, the biologically important transition metals recurrently enriched within the CMa from ancient hydrothermal chert must reflect the chemical composition of the habitats of early life, and be rich in, for instance, Fe, V, Cr, Cu, Ni, and Co, elements integral to the microbial metallome.
In the frame of an international collaboration, a quantitative nano-imaging of metal traces in a solid was applied to an ancient microfossil detected from INACMa samples. This is a recent development arising from the construction of hard X-ray nano-probes dedicated to X-ray Fluorescence (XRF) imaging on upgraded third generation synchrotrons. Micrometer sample preparation for trace analysis is a fundamental part of the required developments to capitalize on the reduced minimum detection limits (MDLs). Practical guidelines led us to propose a customized use of Focused Ion Beams backed by state of the art Monte Carlo XRF modelling to achieve the preparation of new samples and certified standards. The usefulness of these developments was illustrated by the first detection of Ni traces in ancient microfossils. A list of feasibility checks provides a means of achieving below 5 ppm MDLs for acquisition-times of 10 seconds with an analytical precision better than 10%.
Exceptionally well-preserved microbial morphologies made of CMa have been detected in samples from the INACMa project. Studying the CMa in high resolution, we can suggest that these microbes inhabited a Paleoarchean serpentine-hosted cryptic habitat – and therefore most likely a primitive chemoautotrophic ecosystem – that has very profound implications on our understanding of the very early scenarios for life. This further extends our knowledge on the early fossil record.
The obtained results, i.e. an understanding of microbial features in specific primitive habitats and their nano-scale composition (trace-elements and IN), suggest a metal-based bio-geochemistry for the organisms and add some constrains (in terms of chemical composition of the fluids) to the otherwise very basic characterizations of early habitats.
UniBO is now also known for having a research team and lab led by the proponent which studies early life and is involved in new H2020 projects.

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