EARTHTIME: A community-based effort towards high-precision calibration of earth history

Geological time is customarily treated as an independent variable; deductions and conclusions are made assuming that the geological timescale as given is precise and accurate. Current geological timescales are based on data of variable quality, commonly averaging dates obtained by different techniques, with differing (though often ignored) absolute uncertainties. Consequently, the greatest uncertainty in most analyses of geologic and evolutionary rates is the timescale itself. Recent advances in geochronology and correlation methods now allow us to reframe research into the timing and rates of geological and biological processes in deep time, producing a newly calibrated geological timescale with significantly improved accuracy and precision standards commensurate with new and emerging geochronologic and chronostratigraphic methodologies. To address these issues the EARTHTIME initiative has been proposed as a new community-based effort to focus attention on the calibration of at least the last 800 million years of earth history. This will allow earth scientists to address a whole new series of questions that rely on knowledge of precise rates of biological, geological, and climatic change. Two EARTHTIME workshops have been held, the first to discuss the need for better integration of geochronology and paleontology and the second, on intercalibration of the U-Pb and Ar-Ar chronometers. As an outgrowth of these two meetings we have proposed the production of a mixed Pb-Pb-U-U spike for distribution to the international community and the sponsorship of a community wide intercalibration experiment using standard material (see Heizler et al., and Condon et al., this session). Community support is growing and we expect that this effort will fundamentally change our knowledge of the distribution of time in the rock record and give us unprecedented insight into the rates of geological, biological, and climatic processes in deep time. The EARTHTIME concept has wide application to all parts of the geological record and the Earth Sciences. Intercalibration of astronomical and radioisotopic time K. KUIPER, A. DEINO, F. HILGEN, W. KRIJGSMAN, P. RENNE AND J. WIJBRANS Utrecht University, Faculty of Geosciences, The Netherlands (kkuiper@geo.uu.nl, fhilgen@geo.uu.nl, krijgsma@geo.uu.nl) Berkeley Geochronology Center, Berkeley, USA (adeino@bgc.org, prenne@bgc.org) Vrije Universiteit Amsterdam, Isotope Geochemistry, The Netherlands (Jan.Wijbrans@falw.vu.nl)