"Scientists calculate that about 95 percent of marine species, and an uncountable but probably comparable percentage of land species, went extinct in a geological heartbeat"
"So what happened 252 million years ago to cause those physiological stresses in marine animals? Additional clues from carbon, calcium and nitrogen isotopes of the period, as well as from organic geochemistry, suggest a “perturbation of the global carbon cycle,” the scientists’ second paper concluded — a huge infusion of carbon into the atmosphere and the ocean."
—Read all about the Great Dying, our worst paroxysm. Also, paroxysm is a delightful word that I do not recall encountering before.