Major extinction level events are associated with carbon dioxide level imbalances. The first event was caused by the evolution of Cyanobacteria that consumed carbon dioxide down to the point that the Greenhouse Effect could no longer maintain sufficient temperatures on Earth to sustain most life. Other extinction level events were caused by excessive amounts of carbon dioxide release from very large scale volcanic activity that caused spikes in temperatures and in ocean acidification.
Note: That the dinosaurs were driven to extinction by an asteroid is somewhat doubtful because the fossil bearing zone below the K-T boundary popularly called the 3-meter gap is generally barren of dinosaur fossils. Whether their extinction was complete by the time of the asteroid strike is not yet known. It is certain, however, that the extinction was in progress... “Long before the Chicxulub impact, a different disaster was underway on the other side of the planet. Back then, India was its own landmass near Madagascar (off of the East Coast of what is now Africa). The Deccan volcanic eruptions there would ultimately belch out some 1.3 million cubic kilometers (300,000 cubic miles) of molten rock and debris. That’s more than enough material to bury Alaska to the height of the world’s tallest skyscraper. Gases spewed by similar volcanic outpourings have been linked to other major extinction events.”