THE EARTHTIME INITIATIVE: PROGRESS AND PROMISE

The EARTHTIME initiative is a community-based effort to focus attention on the calibration of at least the last 800 million years of Earth history. This requires using a unified, multi-chronometer (radioisotopic and cyclostratigraphic) approach integrated with paleobiological and climate proxy datasets, enabling earth scientists to pose questions that rely on knowledge of precise rates of biological, geological, and climatic change. The goals of the first phase were to: 1) forge links between geochronologists, paleontologists, and stratigraphers, and identify key intervals of Earth history for which higher resolution temporal constraints are essential, 2) develop the tools necessary to calibrate earth history using both U-Pb and ⁴⁰Ar/³⁹Ar geochronology and, 3) to develop a program of education and public outreach. We now have more than 300 members and a parallel effort in Europe.

A major effort has been to minimize and/or eliminate inter-laboratory and inter-technique bias. The U-Pb community has manufactured, distributed, and calibrated a ²⁰⁵Pb-²³³U-²³⁵U tracer solution and synthetic zircon solutions to monitor long-term analytical reproducibility. In addition, a new open-source data reduction and age calculation software ,U-Pb_Redux, is available for transparent reduction, analysis, and archiving of all U-Pb geochronological data with links to global databases and will function as a teaching tool.

The ⁴⁰Ar/³⁹Ar community has undertaken two major inter-laboratory comparison experiments involving more than twenty labs. Under controlled experimental conditions, variability between laboratories for relative ages of commonly used standards is significantly outside individually quoted precision. Ongoing determination of inter-laboratory bias is a priority.

EARTHTIME outreach activities include development of curriculum for middle- and high-school students and hands-on exercises. Our goal is to seamlessly integrate U-Pb, ⁴⁰Ar/³⁹Ar, and cyclostratigraphic techniques to construct high-fidelity records of earth history. Ultimately, the level of community involvement in general, and forging alliances between geochronologists and paleontologists in particular, will determine the degree to which the goals of EARTHTIME are realized.