Calibrating the Cryogenian

Abstract

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.