Answer:
The Mass Extinction at the end of the Permian Period was the result of volcanic eruptions.
Step-by-step explanation:
The Permian was a period when there was lush vegetation around the globe, high diversification among the animals, and many lineages that later gave rise to more familiar animal and plant groups that occurred during this time. This picture of the world suddenly ended though, and it did with the biggest mass extinction that we know off. The reason is still not 100% confirmed, but it is most commonly accepted that it was masive volcanic eruptions that caused this.
In what is now Siberia, there was a giant super-volcano, and this ancient volcano is seen as the primary reason for the rapid changes in the living conditions but also contributing to the activation of other volcanoes. It is believed that the amount of carbon dioxide, sulfur dioxide, ashes, and pyroclastic material released was so massive that the whole Earth was wrapped in them, blocking the sunlight, changing the climate rapidly, contributing the massive acidic rainfall, etc. The end result was near extinction of almost all life, and the survivors were just small and highly adaptable organisms that later gave rise to the organisms of the Mesozoic and Cenozoic.