Using light to describe the ancient world

X-ray fluorescence chemical map of an ancient teleost fish. From Gueriau et al. PLoS One 2014: doi:10.1371/journal.pone.0086946.g001

X-ray fluorescence chemical map of an ancient teleost fish. From Gueriau et al. PLoS One 2014: doi:10.1371/journal.pone.0086946.g001

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:

 

Figure 1. Synchrotron X-ray fluorescence mapping of major-to-trace elements in fossils from the OT1 Lagerstätte. (A–C) Optical photographs of the specimen of the shrimp Cretapenaeus berberus MHNM-KK-OT 01a (A), the usual teleost fish MHNM-KK-OT 02 (B) and the newly identified teleost fish MHNM-KK-OT 03a (C). (D–F) False color overlays of elemental distributions reconstructed from a full spectral decomposition of the synchrotron raster-scanning data. (D) False color overlay of neodymium (red), yttrium (green) and iron (blue) distributions from the shrimp (scan step: 100×100 µm2, 26,751 pixels). (E) False color overlay of neodymium (red), strontium (green) and iron (blue) distributions from the characteristic teleost fish (scan step: 125×123 µm2, 21,120 pixels). (F) False color overlay of neodymium (red), yttrium (green) and iron (blue) distributions from the newly identified teleost fish (scan step: 100×100 µm2, 50,851 pixels). Images demonstrate the strong elemental contrast between fossil skeletal and soft tissues. The yellow and red squares in C indicate the two areas that were mapped at higher spatial resolution in Fig. 2. The scale bar is 5 mm and applies to all panels. doi:10.1371/journal.pone.0086946.g001

Figure 1. Synchrotron X-ray fluorescence mapping of major-to-trace elements in fossils from the OT1 Lagerstätte. (A–C) Optical photographs of the specimen of the shrimp Cretapenaeus berberus MHNM-KK-OT 01a (A), the usual teleost fish MHNM-KK-OT 02 (B) and the newly identified teleost fish MHNM-KKOT 03a (C). (D–F) False color overlays of elemental distributions reconstructed from a full spectral decomposition of the synchrotron raster-scanning data. (D) False color overlay of neodymium (red), yttrium (green) and iron (blue) distributions from the shrimp (scan step: 100×100 µm2, 26,751 pixels). (E) False color overlay of neodymium (red), strontium (green) and iron (blue) distributions from the characteristic teleost fish (scan step: 125×123 µm2, 21,120 pixels). (F) False color overlay of neodymium (red), yttrium (green) and iron (blue) distributions from the newly identified teleost fish (scan step: 100×100 µm2, 50,851 pixels). Images demonstrate the strong elemental contrast between fossil skeletal and soft tissues. The yellow and red squares in C indicate the two areas that were mapped at higher spatial resolution in Fig. 2. The scale bar is 5 mm and applies to all panels. doi:10.1371/journal.pone.0086946.g001

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

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Tag Cloud

%d bloggers like this: