The end-Permian mass extinction, and the one that preceded it by nine 9 million years, the end-Guadalupian mass extinction, were both related to , which caused an episode of greenhouse warming and the onset of .

The end-Permian mass extinction, and the one that preceded it by nine 9 million years, the end-Guadalupian mass extinction, were both related to flood basalt eruptions, which caused an episode of greenhouse warming and the onset of deep sea anoxia.

Explanation:

The Permian-Triassic mass extinction was a very large mass extinction of plant and animal species that occurred about 251 million years ago, during the transition from the Permian to the Triassic. Several large-scale extinctions are known in Earth's history, of which the Permian-Triassic mass extinction is the largest.

95% of all marine species and about 70% of terrestrial vertebrates died out at the Permian / Triassic transition. It was also the only time that the insects also became extinct on a large scale; about 1/3 of all insect species disappeared during the Perm-Triassic mass extinction.

It is now believed that this extinction wave occurred within a very short time (about 1 million years) by geological standards. Evidence of a less severe wave of extinction, 9 million years earlier, has also been found in Greenland.

The Permian-Triassic transition was characterized by intensive volcanism. During this period, the Siberian Steps, a 200,000 km² basalt plateau, literally arose from the most extensive volcanic activity in Earth's history. As a result of this volcanism, the climate may have changed enough to produce a mass extinction.

i think it's severe storms but i might be wrong