Final answer:
The Great Dying, or the Permian-Triassic extinction event, was likely caused by volcanic eruptions forming the Siberian Traps, leading to global warming, acid rain, and oceanic anoxia, which contributed to the extinction of 85 percent of marine species and numerous terrestrial species.
Step-by-step explanation:
The "Great Dying," also known as the Permian-Triassic extinction event, marked the end of the Permian period about 252 million years ago and was the Earth's most severe extinction event. A leading hypothesis for the cause of this mass extinction is the large-scale volcanic eruptions that formed the Siberian Traps. These eruptions released massive amounts of lava, along with sulfur and carbon dioxide gases into the atmosphere. This likely led to global warming, acid rain, and a decrease in oxygen levels in the oceans, contributing to an inhospitable environment that made survival difficult for many species.
These environmental changes wreaked havoc on the marine ecosystem, with about 85 percent of marine species becoming extinct. The on-land flora and fauna were also severely impacted, with vast numbers of species unable to adapt to the rapid changes. Factors such as climate change, asteroid impacts, and volcanic activity are all considered possible contributors to this and other mass extinction events throughout Earth's history.