Accurate and precise geochronology is fundamental to earth sciences, essential for the quantification of rates and durations of geological processes and in unravelling cause and effect relationships. The 40Ar/39Ar technique has the widest temporal range of any geochronometer, can be applied to many K-rich rocks, and is used to solve key questions in earth, life, and planetary sciences. Modern mass spectrometers generate measurements with analytical uncertainties (precision) much smaller than the uncertainty of the fundamental constants required for age calculations (accuracy). Whilst precision is often better than 0.1%, accuracy is limited to ~ 2.5% due to uncertainties in the decay of 40K and absolute ages of mineral standards. Many of these parameters are based on poorly documented studies from the 1960s and 1970s and need to be improved.
I aim to improve the accuracy of the 40Ar/39Ar system from ~2.5% to ~0.5%, calibrated against SI standards and independent from other geochronometers. Objectives include: (1) develop an SI traceable isotopic standard for measuring absolute abundances of 40K, (2) measure the absolute amount of 40K in mineral standards, (3) measure the natural relative abundances of K isotopes and recalculate the partial decay constant of 40K to 40Ca, and (4) test improvements in technique accuracy with other geochronometers (e.g. U-Pb and astronomical tuning).
The determination of absolute 40K abundances described in this project is complementary to my current project in a Marie Curie ITN that develops a system for measuring absolute abundances of 40Ar. The long overdue measurements for both K and Ar will facilitate the first principles recalibration of the age of 40Ar/39Ar mineral standards, allow a future redetermination of the 40K decay scheme, and improve the accuracy of the 40Ar/39Ar technique. Ultimately, I aim to deliver the tools with which earth scientists will 'dissect' deep geological time with hitherto unattainable resolution.