How not to study fossil biomolecules

The search for fossil biomolecules often requires combining many techniques to properly characterize their chemical composition. Recently, it was suggested in 6 papers that conventional Raman spectroscopy (i.e., equipped with a 532 nm laser as the excitation source under continuous illumination) can be used alone to identify diverse remnants or derivatives of biomolecules in animal fossils, with important implications for both evolutionary events and fossilization processes. Unfortunately, the reported claims are not supported by the spectroscopy data provided, which actually result from instrumental artefacts and data processing. Here, we outline the limitations of Raman spectroscopy with respect to the identification of biomolecules in fossil materials, and then describe in detail the origin of the misinterpreted signal. Conventional Raman spectroscopy alone cannot be used to identify fossil biomolecules. Instead, non-conventional Raman spectroscopy, mass spectrometry and infrared and X-ray absorption spectroscopy techniques, are successfully used by paleontologists to identify fossil biomolecules that help understanding both the history of life and the mechanisms of fossilization.