Dinosaurs, the “terrible lizards” that dominated the planet for 150 million years, are perhaps best known for how they died. The asteroid strike that snuffed out most of their kind 66 million years ago has become a source of endless fascination.

But it turns out that dinosaurs rose to prominence in the first place thanks to the worst crisis in the history of life on Earth. About 252 million years ago, intense volcanic activity spewed tons of carbon dioxide and other greenhouse gases into the atmosphere, and the heat ignited coal beds that threw even more ash and particulates into the air. The cataclysm blotted out the sun, acidified the oceans, spurred global warming, and even reduced oxygen levels in the