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Dating carbonaceous matter in archean cherts by electron paramagnetic resonance
M Bourbin1, D Gourier, S Derenne
1Biogéochimie et Ecologie des Milieux Continentaux, UMR CNRS 7618, Université Pierre et Marie Curie, Paris, France.
Astrobiology
|February 13, 2013
Summary
Electron paramagnetic resonance (EPR) can determine the syngeneity of organic matter in ancient cherts. This method helps date primitive organic matter and aids exobiology studies, even on samples from Mars.
Area of Science:
- Geochemistry
- Geochronology
- Exobiology
Background:
- Ancient geological materials, especially Archean cherts, are prone to contamination.
- Establishing the syngeneity of organic matter in mineral matrices is vital for studying early life.
- Electron paramagnetic resonance (EPR) is explored as a tool to assess organic matter syngeneity in ancient rocks.
Purpose of the Study:
- To assess the syngeneity of organic matter in ancient cherts using EPR.
- To establish a correlation between Precambrian sample age and EPR signal shape.
- To investigate the effects of thermal treatments and metamorphism on EPR signals as syngeneity proxies.
Main Methods:
- Utilized electron paramagnetic resonance (EPR) spectroscopy on Precambrian chert samples.
- Correlated EPR signal shape with sample age and subjected samples to controlled thermal treatments.
- Investigated the impact of metamorphism on EPR signals using Silurian cherts of varying metamorphic grades.
- Prepared and analyzed "contamination-like" mixtures to test detection limits.
Main Results:
- Established a statistically significant correlation between Precambrian sample age and EPR signal shape.
- Demonstrated that thermal treatments of cyanobacteria mimic the EPR signal evolution of thermally treated young cherts.
- Ruled out metamorphism as a confounding factor for cherts older than 2 Gyr, as even highly metamorphosed Silurian samples did not match Archean EPR signals.
- Found that EPR lineshape analysis alone is insufficient for detecting contamination; it requires cumulative thermal treatments.
Conclusions:
- EPR is a powerful and effective tool for studying primitive organic matter in low-metamorphic grade geological samples.
- The method enables the dating of carbonaceous matter in Archean cherts.
- EPR holds potential for future exobiology studies, including the analysis of extraterrestrial samples like those from Mars.
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