Quantification of phosphate in precambrian fossils using X-ray techniques: implications for the rise of animals' hard parts

Full text: The presence of purely organic or biomineralized carapaces among Precambrian fossils brings important information about the ecological relations and the paleoenvironment. In addition, the biomineralization phenomenon can be used in astrobiology for the search for biosignatures of extant or extinct life on Earth or elsewhere. A specific problem is the detection of phosphate, an important component of many animals, being also precipitated by several microorganisms. The phosphate is difficult to be studied using spectroscopic techniques such as Raman or X-ray Fluorescence (XRF) due to specific experimental problems. In this work, the group has developed a synchrotron-based methodology to detect and quantify phosphate in the fossil context, using the phosphorous K-edge XANES spectra (P K XANES). Calibration curves in many different substrates were built and the results obtained for the fossils were interpolated to determine the concentration of P on the carapace. Several fossils were studied using this technique and the detection limit compared with other spectroscopic techniques, such as Raman and XRF. (author)