Scientists have argued over whether the extinction of the dinosaurs was caused by a space impact or by super-volcanic activity which lasted for 1.5 million years. The space impact would have caused sudden large-scale fires and earthquakes. Volcanic activity would have caused a cooling of the atmosphere and acid rain which would be seen in changes to marine and land ecosystems over the 500,000 years before the extinction. As no such changes were identified during this period, the space impact is the only plausible explanation.