The Great Dying, also known as the Permian-Triassic Extinction Event, was a mass extinction that occurred about 252 million years ago. The exact causes of the Great Dying are still the subject of scientific debate, but several factors have been proposed, including:
1. Volcanic eruptions: Large-scale volcanic eruptions are believed to have released large amounts of sulfur and carbon dioxide into the atmosphere, leading to widespread global warming and acid rain.
2. Anoxia: Low oxygen levels in the oceans, caused by the proliferation of microorganisms that consumed oxygen as they decomposed dead organic matter, could have caused widespread oceanic anoxia and contributed to the extinction of marine life.
3. Methane release: The release of large amounts of methane from clathrates (underwater ice formations) could have caused rapid global warming and ocean acidification.
4. Asteroid impact: Some scientists have proposed that an asteroid impact could have caused the extinction, but this theory is still the subject of much debate.
It is likely that a combination of these factors, along with other environmental changes, contributed to the Great Dying and the loss of about 96% of all marine species and 70% of terrestrial vertebrates.