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| Titel |
EPR study of thermally treated Archean microbial mats analogues and comparison with Archean cherts: towards a possible marker of oxygenic photosynthesis? |
| VerfasserIn |
M. Bourbin, S. Derenne, F. Westall, D. Gourier, P. Gautret, J.-N. Rouzaud, F. Robert |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058660
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| Zusammenfassung |
| The datation of photosynthesis apparition remains an open question nowadays: did oxygenic
photosynthesis appear just before the Great Oxidation Event (GOE) of the atmosphere,
2.3 to 2.4 Gyr ago, or does it originate much earlier? It is therefore of uttermost
interest to find markers of oxygenic photosynthesis, applicable to samples of archean
age.
In order to handle this problem, Microcoleus Chtonoplastes cyanobacteria and
Chloroflexus-like non-oxygenic photosynthetic bacteria, were studied using Electron
Paramagnetic Resonance (EPR) spectroscopy, a high sensitivity technique for the study of
organic radicals in mature geological samples (coals, cherts, meteorites...). M. chtonoplastes
and Chloroflexus-like bacteria were sampled in mats from the hypersaline lake "La Salada de
Chiprana" (Spain), an analogue to an Archean environment, and were submitted to
accelerated ageing through cumulative thermal treatments.
For thermal treatment temperatures higher than 620Ë C, a drastic increase in the EPR
linewidth of the oxygenic photosynthetic bacteria (M. chtonoplastes) occurred, as compared
with the anoxygenic photosynthetic one (Chloroflexus-like). The EPR study of a thermally
treated mixture of the two bacteria evidences that this linewidth increase is driven by catalytic
reaction at high temperatures on an element selectively fixed by M. chtonoplastes. Based on
comparative EDS analyses, Mg is a potential candidate for this catalytic activity but its
precise role and the nature of the reaction are still to be determined. The EPR study of organic
radicals in chert rocks of ages ranging from 0.42 to 3.5 Gyr, from various localities and that
underwent various metamorphisms, revealed a dispersion of the signal width for the most
mature samples.
This comparative approach between modern bacterial samples and Precambrian cherts
leads to propose the EPR linewidth of mature organic matter in cherts as a potential marker of
oxygenic photosynthesis. If confirmed, this marker would support the hypothesis of
oxygenic photosynthesis apparition at least 3.5 Gyr ago, long before the GOE. |
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