We know that the Chicxulub asteroid impact 66 million years ago causes massive changes in earth's condition that led to the extinction of the dinosaurs. Or do we? More recent research leads to a possible second culprit, the Deccan Traps, a system of volcanos now in western India. Their activity a few million years before the asteroid showed up caused massive climate change, carbon dioxide poisoning, and acid rain, which may have been the death knell of the dinosaurs and a lot of other species. If this was the case, then the Chicxulub impact could have been just the cherry on top of the mass extinction event that began earlier. We don't yet know, because dating scarce fossils and geological evidence is hard, especially when you are trying to measure a timeline many millions of years ago, not to mention estimating populations of species based on what we know. Scientists have their opinions, and can argue about it for days. Kurzgesagt explains the Deccan Traps and how it would have impacted life on earth before the asteroid showed up.