Final answer:
The Great Dying occurred at the end of the Permian period and is considered the largest mass extinction in Earth's history.
Step-by-step explanation:
The Great Dying, or the Permian-Triassic extinction event, occurred during the Paleozoic era at the end of the Permian period. This mass extinction event is considered the largest in Earth’s history, with estimates suggesting that around 96 percent of all marine species and 70 percent of terrestrial vertebrate species became extinct. It drastically altered the course of evolution and the makeup of Earth’s biodiversity, taking approximately 30 million years for the ecosystem to recover. Factors such as volcanic activity leading to global warming and ocean anoxia are suspected to have played a significant role in the Great Dying, although the exact causes are still debated among scientists. It is believed that extended and widespread volcanic activity, causing a runaway global-warming event and ocean anoxia, played a significant role in this mass extinction.