Mass extinction events are periods in Earth's history when a significant number of species die out in a relatively short time. These events can be caused by various factors, including drastic climate changes, volcanic eruptions, or asteroid impacts. The most famous mass extinction is the one that occurred around 66 million years ago, which led to the demise of the dinosaurs. There have been five major mass extinction events identified, each resulting in the loss of a large percentage of Earth's biodiversity. The Permian-Triassic extinction, about 252 million years ago, is considered the most severe, wiping out approximately 96% of marine species. Understanding these events helps scientists learn about the resilience of life and the impact of environmental changes.