Mass extinction refers to a significant and rapid decrease in the number of species on Earth. This phenomenon typically occurs when environmental changes, such as climate shifts or catastrophic events, disrupt ecosystems. Five major mass extinctions have been identified in Earth's history, with the most famous being the extinction of the dinosaurs around 66 million years ago, likely caused by a meteorite impact. During a mass extinction, many species become extinct in a relatively short period, leading to a loss of biodiversity. This can have long-lasting effects on ecosystems, as the balance of life is disrupted. The current rate of extinction is concerning, with human activities contributing to what some scientists call the sixth mass extinction.