SYNCHROTRON-BASED IMAGING PAST LIFE

Quantitative chemical analyses are rarely undertaken on fossils, despite the potentially valuable information to be recovered. Trace metal biomarkers have shown that discrete elemental inventories can be identified and mapped in fossil organisms that correlate to specific anatomical structures. Such elemental inventories can provide insight to specific biosynthetic pathways. Ideally such analyses measure and map the chemistry of bone, soft tissue structures and embedding rock matrix. Mapping fossils in situ helps place constraints on mass transfer between the embedding matrix and fossil, aiding in distinguishing taphonomic processes from original chemical zonation remnant from the fossil itself. Conventional non-destructive analytical methods face serious problems in this case and most recent technological advances have been targeted at developing nanometer-scale rather than decimeter-scale capabilities. However, the development of Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) at the Stanford Synchrotron permits large specimens to be non-destructively analyzed (1-100 µm resolution) and imaged using major, minor and trace element concentrations. Fossil and extant samples are mounted in a purpose-built sample chamber held on a computerized x-y-z translational stage. For light-element XRF imaging, an X-ray-transparent ∼30-μm thick polyethylene film was placed on the sample chamber, and purged of air with He to minimize scattering and increase signal to the detector. Spectroscopy constrains oxidation state and coordination chemistry of key elements (S, Ca, Cu, Zn, Sr, etc.), providing insight to the endogeneity of chemistry mapped to PPM sensitivity. This precise, repeatable and quantitative technique builds upon decades of research at synchrotron facilities, shedding new light on the chemistry and evolution of life.