The passage suggests that during the 1980s researchers found meteorite impact a convincing explanation for the extinction of dinosaurs, in part because A. earlier theories had failed to account for the gradual extinction of many ocean species at the end of the Cretaceous period B. geologists had, up until that time, underestimated the amount of carbon dioxide that would be released during an episode of explosive volcanism C. a meteorite could have served as a source of the iridium found in a layer of clay deposited at the end of the Cretaceous period D. no theory relying on purely geological processes had, up until that time, explained the cause of the precipitous drop in sea level that occurred at the end of the Cretaceous period E. the impact of a large meteorite could have resulted in the release of enough carbon dioxide to cause global climatic change