Imperial College London
Earth Science and Engineering

The emergence of Eukarya—one of the main domains of life, which includes plants, animals, fungi, and many single-celled organisms—was a major evolutionary milestone in Earth's history. By one billion years ago, all major groups of Eukarya present today had already diverged. Fossils of this age are identified as eukaryotic based on physical features common to all eukaryotic groups, and only rarely do they exhibit features diagnostic of specific eukaryotic lineages. A geochemical technique, Fourier transform infrared spectroscopy (FTIR), characterizes the chemical composition of organic matter my measuring energy absorption patterns. In some cases, these chemical signatures are unique to particular eukaryotic group(s) and can serve as a diagnostic tool. However, the possibilities for signal alteration have not been adequately or systematically explored. Geological processes destroy or rearrange these chemical signatures, potentially leading to incorrect interpretations of fossil identity. I will test the utility of FTIR spectroscopy in deep time by tracking the persistence of spectral signatures in modern eukaryotic specimens through simulated ‘aging’ experiments in the laboratory, as well as in younger eukaryotic fossils of known placement within the eukaryotic tree. I will compare these signatures to older eukaryotic fossils with unknown placement within Eukarya. Applying chemical information to identify early eukaryotic fossils has the potential to clarify evolutionary relationships among the earliest branches of living eukaryotic groups. However, for this tool to be utilized with confidence, the possibilities of signal alteration must be explored. This is best achieved by working from the present into the past— linking spectral signatures of modern groups to their fossil representatives. Only then might the geochemical signatures of some microfossils be used to identify their place within the eukaryotic tree.