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Revealing the chemical composition of whole organic fossils in 3D!

Publication in Science Advances

by Fanny Dubray - published on

An international team led by IPANEMA, and composed of three other CNRS laboratories (ISYEB, IMPMC and LRCP), the University of Lausanne and three synchrotron facilities (SOLEIL and ESRF in France, SLAC at Stanford in the United States) has just shown that it is possible to establish the composition at each point of an organic fossil based on the totally innovative use of a method resulting from fundamental research in X-ray spectroscopy.

Figure: chemistry reveals the preservation of chitin molecular signatures, better preserved on the surface of the ant that was first in contact with the resin.

The study of fossil materials has benefited from 3D X-ray computed tomography for about fifteen years, comparable to medical scanning. Tomography allows the study of microscopic patterns necessary to understand the evolution of species, their physiology and fossilization mechanisms. It leads to "black and white" images indicative of the density of materials, as a medical X-ray shows the relative absorption of different tissues, but does not provide the internal molecular composition of fossils. Other methods, such as X-ray fluorescence imaging, can form a chemical image, but only on flat fossils.

With 3D X-ray Raman imaging, a small fraction of the X-ray energy with which a material is illuminated is transferred to its electrons by inelastic scattering, producing a detectable signal to determine its chemical composition. The team proved that coupling this method with advanced instrumentation using the qualities of focusing, energy resolution and penetration of synchrotron X-rays allowed to obtain the composition at each point of the fossil, in 3D.

The team showed that a 53-million-year-old fossil ant exceptionally preserved in amber had preserved molecular signatures of chitin, an extremely resistant complex sugar used by insects as the main structural component of their exoskeleton. The researchers also discovered that the surface of the insect that had been brought into contact first with resin had been chemically preserved better than the one that had been covered later after the insect’s death.

These results are published in the journal Science Advances.

Postscript :

Reference
R. Georgiou, P. Gueriau, C. Sahle, S. Bernard, A. Mirone, R. Garrouste, U. Bergmann, J.-P. Rueff et L. Bertrand. Carbon speciation in organic fossils using 2D to 3D x-ray Raman multispectral imaging. Science Advances, doi: 10.1126/sciadv.aaw5019

Scientific contacts:
Loïc Bertrand, IPANEMA (CNRS, ministère de la culture, UVSQ; Université Paris-Saclay), loic.bertrand@synchrotron-soleil.fr
Jean-Pascal Rueff, Synchrotron SOLEIL, jean-pascal.rueff@synchrotron-soleil.fr
Uwe Bergmann, SLAC Stanford, bergmann@slac.stanford.edu


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