The document defines extinction as the complete disappearance of a species from Earth. It describes the main types of extinction such as diversity independent, diversity dependent, mass extinction and absolute extinction. The causes of extinction include environmental changes, lowering of species capacity, large numbers of species disappearing over a limited time period, species dying without reproducing, and one species evolving into another species. The significance of extinction is discussed as the origin of new groups, establishing the geological time scale, and providing evidence of evolution.