title: Search for EPR markers of the history and origin of the insoluble organic matter in extraterrestrial and terrestrial rocks.
abstract: The insoluble organic matter (IOM) of three carbonaceous meteorites (Orgueil, Murchison and Tagish Lake meteorites) and three samples of cherts (microcrystalline SiO2 rock) containing microfossils with age ranging between 45 million years and 3.5 billion years is studied by electron paramagnetic resonance (EPR). The age of the meteorites is that of the solar system (4.6 billion years). The purpose of this work was to determine the EPR parameters, which allow us to discriminate between biogenic and extra terrestrial origin for the organic matter. Such indicators should be relevant for the controversy regarding the biogenicity of the organic matter in the oldest cheroot (3.5 billion years) and in Martian meteorites containing microbe-like microstructures. The organic matter of meteorites contains a high concentration of diradicaloid moieties characterised by a diamagnetic ground state S = 0 and a thermally accessible triplet state S = 1. The three meteorites exhibit the same singlet-triplet gap (ST gap) DeltaE approximately 0.1 eV. To the best of our knowledge, such diradicaloids are unknown in insoluble organic matter of terrestrial origin. We have also shown that the EPR linewidth of insoluble organic matter in cherts and coals decrease logarithmically with the age of the organic matter. We conclude from this result that the organic matter in the oldest cherts (3.5 billion years) has the same age as their SiO2 matrix, and is not due to a latter contamination by bacteria, as was recently found in meteoritic samples.
authors.affiliation: Ecole Nationale Supérieure de Chimie de Paris (ENSCP), Laboratoire de Chimie appliquée de l'Etat Solide, UMR-CNRS 7574, 11 rue Pierre et Marie Curie, 75231 Paris 05, France. gourierd@ext.jussieu.fr
authors.forename: Didier
authors.initials: D
authors.lastname: Gourier
authors.forename: Laurent
authors.initials: L
authors.lastname: Binet
authors.forename: Audrey
authors.initials: A
authors.lastname: Scrzypczak
authors.forename: Sylvie
authors.initials: S
authors.lastname: Derenne
authors.forename: François
authors.initials: F
authors.lastname: Robert
mesh_terms: D002244:Carbon / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D019418:Evolution, Chemical; D005118:Extraterrestrial Environment / Q000737:chemistry*; D005580:Fossils; D019110:Meteoroids; D008855:Microscopy, Electron, Scanning; D009930:Organic Chemicals / Q000032:analysis* / Q000302:isolation & purification; D012822:Silicon Dioxide / Q000032:analysis; D012995:Solubility
chemical_list: D009930:Organic Chemicals; D002244:Carbon; D012822:Silicon Dioxide