The geochronology of large igneous provinces, terrestrial impact craters, and their relationship to mass extinctions on Earth

The relationship between sudden catastrophic events and sudden mass extinctions on Earth has attracted a great deal of research effort, including measurements of the absolute and relative ages of these events. The result has been a rapid improvement in the precision and accuracy of radiometric dates for large igneous provinces (LIPs), for which there is now a consensus on the peak eruption times over the last 250 Ma. In parallel there has been a more gradual improvement in the radiometric dates for craters formed by hypervelocity impacts (HVIs) of asteroids and comets with Earth. The absolute ages of the largest craters are known to within a few million years but the ages of many smaller craters are poorly constrained. In addition, whereas relatively few LIPs have formed in the last 250 Ma, at least one HVI crater larger than 20 km diameter has formed on Earth every million years (only 25 such craters have been discovered), so coincidence between the ages of HVI crater formation and ages of mass extinctions is related as much to crater preservation as to coincidence of the events. The difference in quality of geochronology between HVIs and LIPs is the result of differing availability of samples: LIPs cover large areas and present an array of basalt samples suitable for dating, whereas HVI craters are often poorly preserved and present few datable samples. The radiometric data for preserved HVIs and LIPs are now sufficiently precise and accurate for us to be confident that there is no one-to-one correlation between either LIPs or HVIs and global mass extinctions of life on Earth. However, there is a close association between a significant number of Ups and sudden environmental change, and a very close association between at least one massive HVI crater formation and a mass extinction. Further, there is no apparent correlation between HVIs and LIPs and thus no reason to suggest a causative relationship. Finally, the radiometric dating of HVI craters indicates several clusters in the geological record, but the correlation with sudden environmental change is no better than for large craters.