The project consisted of 4 work packages that were designed to study the transformations that microorganisms undergo when they are subjected to silicification (WP-1), diagenesis (WP-2), metamorphism (WP-3) and hydrothermal processes (WP-4). Throughout the project laboratory alteration experiments were carried out, microbial communities in natural hot spring environments were studied, and microfossils in Proterozoic and Archean chert deposits were characterized. We made use of a wide range of in situ analytical techniques (including CLSM, Raman spectroscopy, SEM, TEM, synchrotron-based XRF, XANES, STXM, and micro-CT) to characterize our experimental and natural samples. Currently we are still working on several manuscripts of the various projects. We recently created a dedicated website (
https://www.erc-traces.org/(s’ouvre dans une nouvelle fenêtre)) that highlights all aspects of project TRACES, and contains links to all published papers. Below a few highlights of the 4 work packages are described.
Work packages 1 and 2 focused on silicification and early diagenesis of microbial communities in geothermal silica sinters. A large part of this research was based on extensive field work and drilling operations in the El Tatio geothermal field, Atacama Desert, Chile. In low-temperature zones we traced the progressive silica-entombment of individual sheathed filamentous cyanobacteria from the surface to the interior of an active geyser silica sinter, and subsequently recorded specific steps of degradation during artificial diagenesis in controlled autoclaves. In a second research component, field-based chemical depth profiling into living microbial mats enabled us to study the exact environmental conditions for silica-entombment and conversion to microbialite structures. The third research component focused on the preservation of microbial communities in high-temperature geothermal zones. For this purpose we studied biofilms, mats, and streamers occupying various niches in and along the edges of outflow channels of two geyser systems.
Work package 3 focused on progressive diagenesis and early metamorphism of microbial remains over short to long time spans (from thousands to billions of years). We carried out a core-drilling project in one of the 10-thousand-year old extinct geyser systems, and reconstructed the 3D-evolution of a hydrothermal system over several thousands of years. In the second research component we focused on the preservation of microfossils in Proterozoic cherts. The 1.0 Ga old Angmaat Formation, Baffin Island, Canada, has a complex diagenetic history, enabling comparison of low-temperature alteration effects on suites of microfossils. In-situ analytical techniques were combined to determine alteration steps of individual coccoidal cyanobacterial microfossils.
Work package 4 focused on life detection in the oldest, hydrothermally-influenced, silica deposits on Earth. In such rocks the organic traces of life are often ambiguous because there are many abiogenic microstructures with life-like morphologies - such as self-assembled ‘biomorph’ mineral aggregates and pore space networks – that mimic preserved microorganisms. In the first component of this work package we created silica-carbonate biomorphs in variable aqueous solutions and silica gels, and compared their morphologies with those of microbial cells. We then explored the use of statistical methods to distinguish populations of microfossils from populations of biomorphs and rock pore-networks, and then expanded this into a new quantitative approach for life detection.
