Extinction occurs when a species, such as the Woolly Mammoth or Dodo Bird, no longer has any living individuals. This can happen due to various factors, including habitat loss, climate change, and human activities like hunting. Once a species is extinct, it cannot return, leading to a loss of biodiversity. There have been several mass extinctions throughout Earth's history, with the most famous being the Cretaceous-Paleogene extinction, which wiped out the dinosaurs. These events can drastically alter ecosystems and the balance of life on the planet, affecting many species and their habitats.