We often think of fossils as being solid and three-dimensional body parts, like dinosaur bones or ancient sea shells, and we can imagine these fossils being part of an organism that lived in ancient times. Eventually that organism would have died and become buried under sediment. Sometimes sediment does an excellent job of preserving fossils through deep time. But not always – sometimes the weight of the sediment crushes the fossil almost completely, flattening out the three-dimensional features. Working with flat fossils can be tricky if you are interested in the fine details of these ancient body parts. Pierre Gueriau and colleagues recognised this problem, and described a chemical imaging technique that can better help with visualising these flattened remains.
Gueriau and colleagues used x-ray fluorescence to study crushed fossils. X-ray fluorescence is useful for describing the elemental composition of a fossil. When this elemental information is collected from many thousands of points, there is enough information to build an elemental map. Researchers can visualise the distribution of elements in a fossil by assigning different colours to different elements. So how does this help to visualise the structure of a crushed fossil?
“…Here, we discriminate tissues in exceptionally well-preserved fossils on the basis of their content in chemical elements from majors to traces, in particular trace rare earths and transition metals, and alkaline earths. We exploit the distinct affinities of mineralized tissues and authigenic phases for fixing elements as a source of contrast between hard and soft fossil parts. Our results are based on the identification of spatial distributions of more than twenty elements in entire fossils through synchrotron X-ray spectral raster-scanning…” – Gueriau et al. PLoS One 2014
So, different parts of the fossils actually contain slightly different elemental compositions. Using false colour maps, where different colours correspond to different elements, the authors were able to produce images like this:
The authors were able to produce incredibly detailed maps of fossils because they were using a synchrotron as the source of their x-rays. The high-energy, tightly focused x-ray beam from the synchrotron meant that a great deal of data could be quickly gathered from one tiny spot on each fossil. Repeat several thousand times to produce a map!
#PLOSONE: Trace Elemental Imaging of Rare Earth Elements Discriminates Tissues at Microscale in Flat Fossils http://dx.plos.org/10.1371/journal.pone.0086946
Gueriau P, Mocuta C, Dutheil DB, Cohen SX, Thiaudière D, et al. (2014) Trace Elemental Imaging of Rare Earth Elements Discriminates Tissues at Microscale in Flat Fossils. PLoS ONE 9(1): e86946. doi:10.1371/journal.pone.0086946