Micro- to nanoscale Molecular, Mineralogical, Morphological and isotopic identification of Micro and Macro-fossils. – M6fossils
Micro- to nanoscale Molecular, Mineralogical, Morphological and isotopic identification of Micro and Macro-fossils.
Our planet’s chemistry was modified drastically by microorganisms during the 3 billion years that preceded the coming of land plant (about 400 million years ago). A majority of the fossils of this age remains difficult to interpret in terms of metabolism (intracellular chemical reactions), taxonomy (species), and ecosystems. We aim at constraining the nature of these fossils and of their relationships with their host environment using an arsenal of novel characterization techniques.
Characterization as a means to identify the nature of (micro)fossils and their environmental interactions
Our global objective is to build an integrated and innovative set of methods to identify micro- and macro-fossils for which morphology alone is not diagnostic, and apply these methods to fundamental questions concerning the early evolution of life on Earth, and one of its major consequence: atmospheric oxygenation. Molecules diagnostic of specific metabolisms or classes of organisms (biomarkers) have traditionally been investigated using bulk rock analyses, which has three disadvantages: 1) the molecules cannot be correlated with the morphological features of fossils, 2) their structure and concentration have been altered in the most ancient rocks, which are in turn vulnerable to contaminations, and 3) a variety of biopolymers from distinct organisms fossilize simultaneously, forming a mixture that cannot be resolved using usual bulk-rock techniques. Spectromicroscopy techniques analyzing organic functional groups are not diagnostic as they do not describe molecules completely. Here we develop new mass spectrometry devices, more informative on molecules, with the objective to analyze single fossil microorganisms. Moreover, we lack information on the nanoscale structure of single fossil cells and on post-mortem modifications endured by individual micro- and macro-fossils, which may lead to misinterpreting microscopic morphological features. Furthermore, organic carbon isotope compositions of microfossils have been difficult to interpret in term of metabolism, partly due to possible bias induced by selective preservation of specific classes of molecules. This bias can only be constrained by coupled molecular/isotopic microanalyses. Finally, geochemical and mineralogical signatures of metabolic processes can be found in biominerals (e.g. Fe-oxides, sulfides), but their links with fossils remain elusive. We will perform integrated molecular, isotopic, morphological and mineralogical analyses to constrain the nature of individual fossil cells.
We develop Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS, at UCCS Lab in Lille), and microscale Laser-desorption Laser-ionization Mass Spectrometry (µL2MS at PhLAM in Lille) to analyze the molecular compositions of single cells of micro- and macro-fossils and address possible contaminant distributions. We compare multiple ToF-SIMS ionization sources and their effect of fragmentation of molecules. We upgrade our L2MS instrument to perform high spatial resolution analysis (7-10 µm, µL2MS) and molecular mapping with minimal fragmentation and higher mass resolution (m/z 10k-50k). We use bulk-rock gas-chromatography mass-spectrometry (at LOG in Lille) to constrain the molecules (e.g. resolve isomers) detected on microscale. In parallel, we use advanced (spectro)microscopy methods (micro-infrared, X-ray absorption spectroscopy, Raman, chemical mapping in Transmission Electron Microscopy,…, mostly available in Lille University) to document the structure and composition of fossils and their mineral matrices at the micro- and nano-scales. We perform isotope ratio analyses in bulk rock (at IPG Paris and Biogeosciences Dijon) and at the microscale with SIMS (at CRPG Nancy). We analyze a series of fossiliferous rocks 150 to 3400 million years old. In some of the least thermally mature targets, we will compare the micro- to nanoscale biosignatures of plants, animals, fungi, bacteria, algae, which we will use as criteria to identify much older and ambiguous microfossils. We have selected samples to address the effects of diagenetic and metamorphic transformations, with quartz-hosted fossils whose age gradient is correlated with an increase in organic matter maturity and mineral matrix recrystallization. We investigate the preservation of biosignatures in morphologically identified microfossils (e.g. cyanobacteria) of increasing thermal maturity and age, and in ambiguous microfossils.
Fossil microorganisms older than 1.7 billion years are difficult to identify due to their small size, their simple shape, and their alteration. We studied 1.88 billion year old microfossils within a stromatolite of the Gunflint Formation, Canada. Using nanoscale imaging, we demonstrated the preservation of cellular shapes in filamentous microfossils. Spectromicroscopy allowed us to demonstrate the intimate association of ferruginous intracellular minerals with some microfossil morphospecies. This allowed us to support the hypothesis, which has been debated for the last 60 years that these microfossils were oxygen-producing photosynthesizers (cyanobacteria). Publication Lepot et al. 2017 Nature Communications.
We studied microfossils associated with an Australian Banded Iron Formation from the Great Oxygenation Event (2.4–2.2 billion year old). Although the microfossils are much more degraded than those of the Gunflint, we could evidence a diversity of morphospecies using spectromicroscopy. We have shown fossil microorganisms associated with ferruginous minerals that bear a 56Fe/54Fe isotope ratio diagnostic of an iron oxidation reaction. This suggests that the microorganisms could have been bacteria that oxidized iron in relatively deep waters (Fadel et al., in review).
Finally, we have shown an unexpected quality of preservation in 2.1 billion year old filamentous and spherical microfossils and debated of the biogenicity of putative star-shape microfossils that are intimately associated with these spherical and filamentous microfossils. Lekele Baghekema et al., in prep.
Our ongoing research includes:
- Development of molecular microanalyses in Lille
- Application of molecular microanalyses to Phanerozoic fossils
- Application of molecular microanalyses to Proterozoic microfossils
- Coupling these molecular analyses to spectromicroscopy analyses and to morphological investigation down to the nanoscale
Peer-reviewed publications:
Lepot, K., Addad, A., Knoll, A. H., Wang, J., Troadec, D., Béché, A., and Javaux, E., 2017. Iron minerals within specific microfossil morphospecies of the 1.88 Ga Gunflint Formation. Nature Communications 14890.
Conferences:
Fadel, A., Lepot, K., Riboulleau, A., Nuns, N., and Knoll, A. H., 2017. Draken microfossils: geochemical perspective. Neoproterozoic snowball Earth workshop, IPG Paris.
Lepot, K. Identification moléculaire, minéralogique, morphologique et isotopique des micro- et macro-fossiles aux échelles micro et nano. 2016. Colloque Annuel CNRS Réseau des Stations et Observatoires Marins, Boulogne
We aim at constraining the co-evolution of life and the environments on early Earth, targeting five milestones through life evolution (between 3.4 Ga – 400 Ma, Billion-Million years) linked with important changes in redox conditions and oxygenation. Identifying the fossils of these times has been limited by (1) morphological simplicity, (2) non-diagnostic organic carbon isotope ratio, (3) difficulty to correlate individual fossils with molecular biomarkers analyzed on bulk rocks, (4) difficulty to correlate fossils with geochemical metabolic/environmental proxies from bulk rocks. To overcome these limitations, we will use a combination of micro- to nanoscale characterizations of fossils. We will develop novel microscale molecular methods: Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and microscale Laser-desorption Laser-ionization Mass Spectrometry (µL2MS). Thanks to these innovative techniques we will be able, for the first time, to retrieve molecular information (biomarker and fossil biopolymer composition) on single fossil cells, and to distinguish adjacent cells as well as cell anatomy. These spatially-resolved analyses will identify possible in-lab and weathering contaminations. Complementary nanoscale analytical (spectro)microscopy will be used to analyze anatomy as well as mineral structures informing on post-mortem morphological modifications and biominerals. Metabolic signatures will be investigated using microscale and bulk-rock isotope analyses of organic matter and biominerals. The project builds on the gathered participants’ expertise in the fields of organic and isotope geochemistry, paleontology, nano-mineralogy, mass spectrometry and spectroscopy, and analytical developments.
(A) Our selection of samples will allow us to address the effects of diagenetic and metamorphic transformations, as i) all fossils are preserved in quartz, ii) their age gradient is correlated with an increase in organic matter maturity and mineral matrix recrystallization, iii) 412 Ma to 1.6 Ga samples contain comparable microfossils (e.g. cyanobacteria, algae). (B) The 412-410 Ma samples will allow us to build a database of microscale molecular fingerprints on a large diversity of micro-organisms (cyanobacteria, algae, fungi) and specialized cells of macrofossils (plants, animals) correlated with nanoscale anatomical imaging. This will inform on cell structures and compositions in some of the earliest land plants (412-400 Ma) thus constraining the evolution of biopolymers including lignin, which triggered a rise in pO2 (O2 partial pressure). (C) We will compare morphologically identified microfossils and ambiguous morphospecies in 800-700 Ma old rocks with coupled molecular, textural and isotopic criteria. We hope to identify the relative importance of cyanobacteria and micro-algae in the primary photosynthetic production in order to constrain the role of the evolution of algae in the rise of pO2 of the Neoproterozoic Oxygenation Event, which resulted in the evolution of multicellular life. (D) ~1.6 Ga microfossil assemblages, coincident with the earliest eukaryotic fossils, will be characterized to constrain primary production during a period of reduced pO2 using microfossils of increased thermal maturity. (E) Microfossil assemblages of the Great Oxidation Event and its aftermaths between 2.45 and 1.8 Ga, will be studied to constrain metabolisms in environments characterized by important redox and pO2 fluctuations, with a focus on Fe-biomineralization associated with ferruginous conditions characterizing the ocean of this time period. (F) Organic microstructures (2.7 Ga) and enigmatic assemblages of small and large microfossils (3.0-3.4 Ga) will be studied to document primary production, methane and sulfur metabolisms associated with early anoxic and ferruginous environments together with possible early production of O2.
Project coordination
Kevin Lepot (Laboratoire d'Océanologie et de Géosciences)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partner
UNIV-LILLE1 Laboratoire d'Océanologie et de Géosciences
Help of the ANR 340,000 euros
Beginning and duration of the scientific project:
October 2015
- 48 Months
