Issues

Gently inclined strata of the upper Bylot Supergroup in Edwin Inlet, Baffin Island (Canada). Bangiomorpha pubescens, a fossil red alga and the oldest taxonomically resolved eukaryote, occurs in the Bylot Supergroup and equivalent rocks in northeastern Canada. Recent radiometric dating has tightly constrained the first appearance of this fossil to ca. 1045 million years ago. Image kindly provided by Galen Halverson (McGill University), who with his co-authors in this issue, reviews the methods by which the Proterozoic time scale is dated and provide an up-to-date compilation of age constraints on key fossil first and last appearances, geological events, and horizons during the Tonian and Cryogenian periods. Their article also develops a new age model for a ca. 819–740 Ma composite section in Svalbard. For details, see pages 137–147.