Molecular fossils: new compounds from 4900-year-old wood

 

If you dug up a wooden artefact, how could you tell what type of tree it came from? French chemists have identified unique molecules from an ancient piece of oak that could hold the key.

Pierre Adam and co-workers from the University of Strasbourg, France, used gas chromatography-mass spectrometry to identify triterpenoid molecules, which appear to be related to the natural product oleanane, in a 4900-year-old wood sample collected from river sediments. The discovered triterpenoids are unusual as they only have an oxygen-containing functional group at the C-2 position, while triterpenoids from living trees either have this at C-3 or both C-2 and C-3. This crucial difference could be due to chemical breakdown of the molecules by micro-organisms in the environment where the wood is buried.

The transformation is important, as the structure of the molecules identified today can be directly traced back to the natural molecules that existed in the living wood, so they can be linked. ‘Reliable triterpenoid biomarkers are useful for both archaeological and geochemical studies. These molecular fossils might be useful for tree species differentiation of severely altered wooden items, for example, wood from shipwrecks or in ancient tombs,’ says Adam. He suggests that they could also be used to reconstruct prehistoric vegetation through time and to identify the contribution of oak organic matter to sediments, both of which could give insight into past environmental changes.

Ian Bull, a research fellow in organic geochemistry at the University of Bristol, UK, says the work is ‘a rigorous piece of analytical chemistry research that increases the range of studies where organic geochemical techniques may be usefully applied. I wish more people in this field did work like this, it is really underappreciated and deserves some attention’. The next step for Adam and colleagues is to study ancient samples from a variety of tree species to build up a reliable library of specific molecular fossils, which could be used to identify archaeological woods.