Sub-epsilon natural ²³⁴ U/ ²³⁸ U measurements refine the ²³⁴ U half-life and U-Th geochronology

234 U/ 238 U ratios are used across various fields in Earth science, but their measurement is highly challenging due to the four orders of magnitude difference in isotope abundance between 234 U and 238 U. Here, we develop refined techniques for accurately and precisely measuring 234 U/ 238 U using multicollector inductively coupled plasma mass spectrometry, providing a reproducibility of ±0.08 per mil (2σ). At this sub-epsilon precision level, the half-life of 234 U is refined to 245,670 ± 260 years. For U-Th geochronology, systematic uncertainties from decay constants largely cancel, effectively reducing the uncertainty in the 234 U half-life to ~±25 years. This improved measurement precision consequently reduces total 2σ age uncertainties to ±3 thousand years (kyr) at ~600 thousand years ago (ka) and ±6 kyr at ~700 ka, a substantial improvement over earlier methods with uncertainties of tens of thousands of years.