Mass extinctions are significant events in Earth's history where a large number of species die out in a relatively short period. These events can be caused by various factors, including drastic climate changes, volcanic eruptions, or asteroid impacts. The most famous mass extinction occurred about 66 million years ago, leading to the demise of the dinosaurs and many other species. There have been five major mass extinctions, often referred to as the Big Five. Each event drastically altered the planet's biodiversity and ecosystems. Understanding these extinctions helps scientists learn about the resilience of life and the potential impacts of current environmental changes.