The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ¹³C over 90,000 years, and coincided with a δ¹³C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.

Aging Snowball Earth: Earth's glacial cycles have varied dramatically over time; at one point glaciers may have covered nearly the entire planet. Correlating various paleoclimate proxies such as fossil and isotope records from that time hinges on the ability to acquire precise age estimates of rocks deposited around the time of this so-called “Snowball Earth.” Macdonald et al. (p. 1241 ) report new high-precision U-Pb dates of Neoproterozoic strata in the Yukon and Northwest Territories, Canada, to calibrate the timing of carbon isotope variation in rocks from other locations around the globe. Based on the estimated past positions of where these rocks were deposited, glaciers probably extended to equatorial latitudes. The overlap with the survival and, indeed, diversification of some eukaryotes in the fossil record suggests that life survived in localized ecological niches during this global glaciation.