Impact or eruptions: Are both to blame in the great end-Cretaceous whodunit?

Published in Earth magazine: Few episodes in geologic history are as widely recognized as the Cretaceous-Paleogene, or K-Pg, boundary 66 million years ago. Utter “K-Pg,” “K-T” (for Cretaceous-Tertiary, as it’s still commonly known) or “end-Cretaceous” to any geoscientist and you’re virtually assured of a knowing glance as he or she recalls at least the textbook basics of a large bolide impact and mass extinction that finished off the dinosaurs and gave rise to the Age of Mammals. Mention it to science-interested laymen, meanwhile, and they may conjure images of tyrannosaurs peering over their shoulders in anguish as they flee from streaking meteors.