The rock stratigraphic record exists as a rich, albeit complex and incomplete repository of Earth history, tracing the processes of biological evolution, climate change, oceanic and atmospheric chemistry, sea-level fluctuations, mountain-building and erosion, and basin subsidence. Without a detailed and precise temporal framework, however, the richness of the record, including global stratigraphic correlations, evaluation of cyclicity and rates of regional and global change, major sedimentary depositional hiatuses, and biological extinctions cannot be fully exploited. In the past two decades major advances in U-Pb zircon geochronology have allowed us to evaluate the distribution of time in the rock record and rates of geological processes with unprecedented precision (see Parrish et al., this volume; Davis et al., this volume). While much work has focused on major transitions in Earth history, there is considerable promise for a highly calibrated time scale from the Neoproterozoic to Holocene that will permit increasingly more sophisticated questions to be addressed using the rock record. It has been long appreciated that there are dramatic events in the diversification and extinction of life such as the Cambrian radiation, the end-Permian extinction, and the end-Cretaceous extinction. However, important questions remain regarding the tempo and causes of evolutionary radiation and extinction. For example, what are the durations of mass extinctions? How long does ecological recovery take following a major extinction? Do evolutionary radiations correlate with changes in chemistry and temperature of the ocean-atmosphere system and global climate? Are there relationships between evolution and the aggregation and dispersal of supercontinents? Are apparently abrupt isotopic excursions in seawater chemistry globally synchronous and of similar duration? Although the biostratigraphic record has been historically used to address these questions, we are now moving into an era where an essential test of correlation and tempo will and must be high-precision geochronology of volcanic rocks interlayered with …