The FOURTH mass extinction event happened around 200 million years ago, as the Earth trembled with massive volcanic activity. Temperatures and carbon dioxide levels naturally rose with the increased volcanic activity, instigating massive global warming and ocean acidification. This event killed many ocean invertebrates and large land animals, including Crurotarsans (crocodile-like reptiles) and Temnospondyls (giant amphibians), paving the way for Dinosaurs to rule the land.