Ocean acidity rise linked with mass extinction event in Late Permian period

The Pioneer: "There have been five mass extinctions over the course of life on earth. The largest one, known as the Great Dying, occurred at the end of the Permian period, 252 million years ago. Around 96 percent of earth’s marine species, 70 percent of terrestrial vertebrates and 57 percent of all insect families were completely killed off."