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TRACES Report Summary

Project ID: 646894
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - TRACES (Tracing ancient microbial cells embedded in silica)

Reporting period: 2015-05-01 to 2016-10-31

Summary of the context and overall objectives of the project

Problem being addressed:

Reconstructing the nature and habitat of early life is a difficult task that strongly depends on the study of rare microfossils in the ancient rock record. The preservation of such organic structures critically depends on rapid entombment in a mineral matrix. Throughout most of Earth’s history the oceans were silica-supersaturated, leading to precipitation of opal deposits that incorporated superbly preserved microbial cells. As we trace this record of life back in deep time, however, three important obstacles are encountered; 1) microorganisms lack sufficient morphologic complexity to be easily distinguished from each other and from certain abiologic microstructures, 2) the ancient rock record has been subjected to increased pressures and temperatures causing variable degradation of different types of microorganism, and 3) early habitats of life were dominated by hydrothermal processes that can generate abiologic organic microstructures. The goal of TRACES is to determine whether key types of fossilized microbial life can be distinguished from each other, and from abiological artifacts, in the oldest, most altered part of the rock record.

Importance for society:

TRACES will establish the experimental basis required for the unambiguous identification of microfossils in silica deposits, which is the key to reconstructing the early history of life on Earth. The question will be answered whether the preservation of an ecosystem is biased towards a certain group of microorganisms or to specific favourable environmental conditions. Critical nano-scale differences will be determined between microfossils and abiologic artefacts in hydrothermal settings. The knowledge gained from this research can also be applied to the younger fossil record because it provides a firm basis for any taphonomic study of organic remains in mineral matrices. Overall this work will lead to a better understanding of the evolution of life.

Overall objectives:

TRACES is studying the critical transformations that occur when representative groups of microorganisms are subjected to artificial silicification and thermal alteration. At incremental steps during these experiments the (sub)micron-scale changes in structure and composition of organic cell walls are monitored. This will be compared with fossilized life in diagenetic hot spring sinters and metamorphosed Precambrian chert deposits. The combined work will lead to a dynamic model for microfossil transformation in progressively altered silica-matrices. The critical question will be answered whether certain types of microorganisms are more likely to be preserved than others. In addition, the critical nano-scale structural differences will be determined between abiologic artefacts – such as carbon coatings on botryoidal quartz or adsorbed carbon on silica biomorphs – and true microfossils in hydrothermal cherts. This will provide a solid scientific basis for tracing life in the oldest, most altered part of the rock record.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

TRACES started in May 2015. The first months of the project were focused on recruitment of personnel, and project and field work planning with collaborating scientists Dr. Stefan Lalonde (European Institute for Marine Studies CNRS, Université de Brest), Prof. Kurt Konhauser (University of Alberta), Prof. Juan Manuel Garcia-Ruiz (Instituto Andaluz de Ciencias de la Tierra), and Prof. Martin van Kranendonk (University of New South Wales). This was then followed by the acquisition of high-pressure, high-temperature autoclaves for the planned diagenesis and metamorphism experiments. Two work packages (WP’s) were subsequently initiated. In the Fall of 2015 postdoctoral researcher Dr. Jian Gong started his project within WP-1, and PhD student Joti Rouillard started his project within WP-4. We have also started the first tasks of WP-2.

The aim of WP-1 is to study the compositional variation of key microbial cell wall types as they are subjected to artificial silicification, and to compare these characteristics with those of silicified microbial communities in natural hot spring sinters. In order to achieve this, during 2015 and 2016 we have successfully cultured various cyanobacterial and algal cell types and have worked out different protocols of silicification (this also included the Master student M1 project of Myriam Agnel). These steps of silica entombment are now being studied using time-lapse optical microscopy, Raman spectroscopy, SEM and TEM. In the summer of 2016 we also successfully carried out field work in Iceland and obtained natural silica sinters that contain entombed cyanobacteria. We are currently comparing these natural samples with our artificially produced silica-entombed cyanobacteria. These detailed observations will soon generate insights into the factors that influence the initial preservation of microbial cells in silica deposits.

The aim of WP-4 is to study the structure and composition of artificially metamorphosed organic carbon-enriched silica biomorphs, and compare these characteristics with those of artificially metamorphosed silica-entombed microorganisms and natural organic microstructures in Archean hydrothermal cherts. In order to achieve this, during 2015 and 2016 we have generated a wide variety of silica-carbonate biomorphs under a range of chemical conditions and have studied them in detail using SEM. For instance we are able to generate spherical or filamentous structures that strongly resemble microbial cells. In the summer of 2016 we also successfully carried out field work in the Western Australia, and collected a suite of hydrothermally-influenced Archean cherts. We are currently studying the characteristics of putative microfossils and carbonaceous materials in several of these samples and earlier obtained samples (this included Raman spectroscopy work involving Master student M2 Selmia Esselma and Master student M2 Clement Jauvion). The next step is to compare these samples with our experimentally produced artefacts. This work is critical for microfossil identification in the oldest rock record on Earth.

The aim of WP-2, which started in the summer of 2016 is to study the changes in structure and composition of silicified microorganisms at different stages of artificial diagenesis, and to compare these characteristics with those of altered microbial communities in recrystallized hot spring sinters. In order to achieve this, we have started with long duration alteration experiments in dedicated autoclaves. The results of these experiments will be studied with high-resolution analytical techniques during reporting period 2, and will be compared with a suite of natural diagenetic silica samples.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The proposed work will generate a wealth of information on the reactions and interfaces between organic compounds and silica matrices. It is thus envisioned that some of the structures produced in the experiments could lead to new bio-inspired hybrid materials.

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