The Permian–Triassic extinction event, informally known as the Great Dying,was an extinction event that occurred 250 million years ago, forming the boundary between the Permian and Triassic geologic periods. It was the Earth’s most severe extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. Researchers at the University of Calgary believe they have discovered evidence to support massive volcanic eruptions that burnt significant volumes of coal, producing ash clouds that had broad impact on global oceans. Interesting enough there is a “coal gap” from this era. Coal deposits dating from this time are few.