Potassium-argon (K-Ar) and argon-argon (⁴⁰Ar/³⁹Ar) methods are widely used to date rocks and minerals, constraining the timing and rates of geological processes, but their ultimate accuracy and precision have long been held back by uncertainties in the decay of ⁴⁰K and in how we calibrate the neutron irradiation step in the ⁴⁰Ar/³⁹Ar technique.

Recently, a novel Bayesian approach was used to re-evaluate all four decay branches of ⁴⁰K by cross-calibrating the ⁴⁰Ar/³⁹Ar with the uranium-lead (U-Pb) method. Because U-Pb is known to a higher confidence, aligning these approaches yields a precise estimate of the ⁴⁰K decay constants.

At the same time, advances in noble-gas mass spectrometers allow for the dating of historically observed eruptions with high precision. The famous 79 CE eruption of Mt. Vesuvius, can serve as a 'time-stamp' to check these decay constants and can be used as a direct geological comparison to the direct counting methods used in the physics community.