SYSTEMATIC ERRORS IN THE CONTEXT OF THE EARTHTIME INITIATIVE

The Earthtime initiative presents a variety of exciting challenges to the geological and geochronological community. First and foremost it calls upon groups with diverse backgrounds to seek a means to interact in a positive and truthful fashion to advance our knowledge of deep-time processes with an unprecedented level of community spirit. Both philosophical and analytical advances are required to achieve a geological timescale that is calibrated to ca. 0.1% precision. In this context, the evaluation of systematic errors between systems and within disciplines requires significant attention. As an example the 40Ar/39Ar community is faced with standards and unknowns with different chemical compositions and relies on making important corrections on materials that yield isotopic compositions vastly different from commonplace silicates. Compromises between standards and unknowns are necessary toward efficient use of reactor time and costs, but can lead to systematic errors. To this end, the 40Ar/39Ar facilities need to build on a growing synergy to inform and communicate critical information that allows an overall increase in expectations and knowledge to overcome analytical issues that cause systematic errors. As and example, a simple compilation of interfering reaction correction factor data for a given reactor will identify the degree of spread existing amongst the laboratories for a parameter that should be essentially constant. Recognition by the group that certain common minerals like biotite often give inaccurate apparent ages compared to sanidines from the same eruption can lead to an understanding of the cause and perhaps a cautious use of certain data in general. In addition, use of biotite as a fluence monitor likely leads to systematic errors related to recoil loss of 39Ar. The entire suite of basic analytical and statistical protocols need more attention by an interactive group of labs in order to identify advantages and disadvantages that can be standardized without the loss of personal decision making. This latter issue requires a fairly substantial change in how geochronology labs go about business as usual, but ultimately will increase the reproducibility of data between all laboratories.