Extinction happens when every single member of a species dies, and no more of that kind of animal or plant exists anywhere on Earth. When the last dinosaur died 65 million years ago, dinosaurs went extinct. When the last dodo bird died in the late 1600s, dodos became extinct forever.

Extinction is permanent and final. Unlike endangered species, which still have living members that might recover with protection, extinct species are gone completely. You can't bring them back. Scientists might have fossils or old photographs, but the actual living creatures have vanished from the planet.

Species can go extinct for many reasons. Sometimes dramatic events cause mass extinctions: the asteroid that killed the dinosaurs wiped out about three-quarters of all species on Earth. Other times extinction happens gradually, when animals lose their habitat, can't find enough food, or can't adapt to changing conditions quickly enough.

Extinction is a natural part of Earth's history: roughly 99 percent of all species that ever lived are now extinct. However, human activities like habitat destruction, overhunting, and pollution have accelerated extinction rates dramatically. Many scientists work to prevent modern extinctions by protecting endangered animals and their habitats before it's too late. Once extinction happens, there's no second chance.