The mass extinction event 66 million years ago between the Cretaceous and Paleogene periods decimated non-avian dinosaurs, although the primary cause of this extinction has been intensely debated. There was a period of intense volcanism in the Deccan Traps of present-day India that preceded the extinction event. These eruption events are thought to have produced millions of cubic kilometers of magma over a period of 700,000 years. The climatic effects of these eruptions have been a suspected cause of this extinction event (and other previous extinction events) by contributing to global warming and stress on ecosystems. Another suspected cause of this extinction is an asteroid impact, which left a 180- to 200-kilometer-diameter crater in the present-day Gulf of Mexico. The so-called Chicxulub impact occurred in carbonate and sulfate-rich sediments, and ejected and globally dispersed large amounts of dust, ash, sulfur and other atmospheric aerosols. The result of this impact would have led to prolonged periods of screening of sunlight and global cooling. So the question has persisted — was it the heat of volcanism or the cooling effects of the impact that caused the end-Cretaceous extinction?

A team of scientists led by Alfio Alessandro Chiarenza at the Imperial College London looked to answer this question quantitatively by testing each extinction scenario. The team used climate and ecological modeling tools to explore how a large impact and extensive volcanism would have affected dinosaur habitats and life on Earth. Chiarenza and colleagues demonstrate that the Chicxulub impact caused substantial detrimental effects on dinosaur habitats through global cooling (also described as an impact winter) by as much as 67°C in the most extreme scenarios simulated. Conversely, no extinction could be modeled using various Deccan volcanism scenarios alone. In fact, the Deccan volcanism may have acted as a buffer against negative effects on global ecosystems and climate by partially counteracting the global cooling caused by the impact. In this way, the Deccan volcanism could have actually promoted the survival of many species and the rapid recovery of others. Because of this, the team concludes that an asteroid impact is the likely primary cause of the end-Cretaceous extinction. READ MORE