Huge volcanic eruptions and the emission of enormous amounts of carbon dioxide were responsible for the onset of mass extinction at the end of the Cretaceous period, preceding the famous Chicxulub meteorite impact, according to a study published in Nature Communications this week. The findings, which stem from a detailed analysis of fossils in Antarctica, indicate a double kill mechanism over a period of a few hundred thousand years.
Non-avian dinosaurs, along with three-quarters of the planet’s species, were wiped out during a mass extinction event at the boundary of the Cretaceous and Paleogene periods, approximately 66 million years ago. The cause of this event is still debated, with many citing the impact of the giant Chicxulub meteorite as the primary cause, and the eruption of the massive Deccan Traps volcanic province in India as a secondary mechanism. However, the close timing of these two events, and incomplete fossil records, make them difficult to distinguish.
Sierra Petersen and colleagues study the extinction event in a high-quality, complete fossil record from Seymour Island, Antarctica. Using a new geochemical approach - carbonate clumped isotope palaeothemometry - they are able to more accurately calculate changes in temperature recorded in the shells of molluscs across the Cretaceous-Palaeogene boundary. The authors show that species extinction coincided with two rapid spikes in temperature, with the first event being synchronous with the onset of volcanism at the Deccan Traps, and the second, smaller event more similar in timing to the actual Cretaceous-Palaeogene boundary and Chicxulub meteorite impact.
The authors propose that the pre-boundary extinction event increased ecosystem stress, making it more vulnerable to a second event once the meteorite struck. However, separating the respective roles of volcanism and meteorite impact regarding this second event remains difficult.