Shedding synchrotron light on the fossil record of early plant evolution

The evolution of land plants transformed the surface, atmosphere and ocean of our planet - by fixing carbon through biosynthesis and increased rates of weathering, as well as through establishing a terrestrial environment habitable by animals. Our understanding of how this was brought about rests less on primitive living plants (mosses, liverworts and hornworts) whose evolutionary relationships are poorly understood but, rather, from the microscopic fossil remains of the earliest plants. Two fossilization mechanisms have provided us with unique insights: (i) the snapshot of a hot vent community in the Late Devonian Rhynie Chert where the neighboring plants were enveloped and preserved in minerals from the hot fluids, and (ii) the charcoalification of plants by wildfires in a number of much older deposits through the Silurian and Devonian. The process of charcoalification is instant fossilization - it makes plant material chemically inert and physically brittle but resistant to bacterial decay and preserves anatomical structure to the cellular level - making fossils preserved in this way an unparalleled archive in of plant evolutionary history.

Ancient charcolified remains of primitive land plants hold insights into their anatomy to the cellular level, but unlocking this information is very difficult. This invaluable material has traditionally been studied by destructively dissection, yielding glimpses of the internal anatomy along cracks that open up in chance orientations. The overall anatomy has to be pieced together by destroying many specimens and the linkage between internal structures are inferential; many structures are never revealed at all.

The obvious alternative is to use non-invasive computed tomography - CT scanning. We introduced a very high resolution method in 2007 of studying charcolified remains of advanced seed and flowering plants using a synchrotron - a kind of particle accelerator. However, the results of analyses of the most ancient land plant remains were terrible - crystals of pyrite (fools gold) have grown within the cell spaces of the fossil remains and the huge difference x-ray absorption between the pyrite (high absorption and scattering) and the charcoal (extremely low absorption) making it impossible to make out any anatomical structure.

Since 2007 there have been improvements in the synchrotron beamline measurement technology, but also in the processing of the data that it collects. In particular, the stage in which the raw measurements are converted to x-ray slices, has been improved with filtering algorithms that allow us to see the anatomy of the fossil in pin-sharp detail.

Our project will entail optimising the measurement parameters and of algorithms involved in the data processing stages, through collaboration with our long-standing Project Partner Prof Marco Stampanoni at the Swiss Light Source Synchrotron - who build the instruments and program the algorithms for data processing. We will exploit these advances in CT scanning new material of early plant remains that we will recover from the critical fossil deposit in Shropshire. We have extensive experience of computer modelling of fossils from synchrotron data and we will analyse computer models of the fossils, dissecting them virtually to better understand the anatomy and physiology of these early plants, in intimate collaboration with the world expert in the biology of these organisms, Prof Dianne Edwards FRS. This work will allow us to understand the sequence of evolutionary steps in early land plant evolution and, in turn, this work will contribute to our understanding of how land plants transformed the planet, and may also prove pivotal in resolving controversy concerning the evolutionary relationships of their living relatives.

The principle method of disseminating the results of this research will be through a number of publications in a high impact peer-reviewed journals, supported by a project-specific web page and conference presentations. Contributions will be made to in-house publications at the Paul Scherrer Institut and the Joint Users Meeting to present the improvements of the technology to other beamline scientists. Disseminate to the public will be achieved through alerts of newsworthy results to press officers and publishing in 'general audience' venues such as Planet Earth. The PDRA is a regular contributor to an online science magazine, through which the research can be publicised. In addition, Earth Sciences (Bristol) have an established staffed outreach programme aimed at both school and college students (funded by the Heritage Lottery Fund) with which we will work. We will also strongly encourage the PDRA to participate in the Researchers in Residence scheme (http://www.researchersinresidence.ac.uk).

The questions at the core of our project bear directly on our understanding of the origins of the terrestrial environment that surrounds us. What were the earliest plants like, how did they cope physiologically with the harsh environment of terrestrialization, and how did these miniscule organisms bring about such a dramatic shift in the chemistry of the atmosphere and the oceans? Fundamental curiosity about these big questions extends well beyond academic beneficiaries into the wider public, and research combining this with a particle accelerator and ancient fossils preserved in the earliest wildfires to ravage the terrestrial environment provides an excellent vehicle for engaging general audiences, including non-scientists and children, with fundamental yet accessible and exciting NERC-funded science. Means by which we will ensure that we engage with these wider audiences are:

1. Distribution of press releases through Eurekalert and AlphaGalileo, leading to dissemination of information via mass media and blogs. The investigators have been trained and have an excellent track record of effective promotion and presentation of their research using these methods, with previous press releases generating worldwide newspaper reports, features on news websites, blog postings, local, national and international radio interviews, as well as national and international television and documentaries. The PI and PDRA has already the NERC media training course.

2. We will develop project specific webpages describing the significance of our research and progress made in the project, written in non-technical language. As part of this we will produce a YouTube-hosted movie encompassing the stages of research, from fieldwork, to laboratory recovery of the fossils, their analysis at the synchrotron beamline and the subsequent computed tomographic study, demonstrating how our evolutionary conclusions are made through every step of the process. The computed tomography lends itself particularly well to this kind of media and, hence, our work has featured in a number of documentaries including the recent 'First Life'.

3. Through the auspices of the Bristol Dinosaur Project , a Heritage Lottery Funded project delivering Earth Sciences outreach to local schools and adult audiences, we will present our work to local schools and also bid for an interactive display at the Bristol Festival of Nature.