Extinction is the complete disappearance of a species from Earth. It occurs when the last members of a species die because they cannot acquire the food, water, shelter, and/or space necessary to survive. A species may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Extinction is a natural part of evolution, but sometimes it happens at a much faster rate than usual. Human intervention is causing rapid extinction, and current rates of human-induced extinctions are estimated to be about 1,000 times greater than past natural (background) rates of extinction, leading some scientists to call modern times the sixth mass extinction.

Key points about extinction include:

• Mass Extinctions: The fossil record reveals five unusually large extinctions, called mass extinction events, each involving the demise of vast numbers of species. These conspicuous declines in diversity are referred to as mass extinctions; they are distinguished from the majority of extinctions, which occur continually and are referred to as background extinction.

• Causes of Extinction: Many species have become extinct because of hunting and overharvesting, the conversion of wetlands and forests to croplands and urban areas, pollution, the introduction of invasive species, and other forms of human-caused destruction of their natural environments.

• Impact of Extinction: Our planet is dependent on an interconnected system, and if we lose one species, it can impact the whole system. Scientists are racing to catalogue the biodiversity on Earth, working against the clock as extinctions continue to occur.

• Endangered Species: Endangered animals and plants are at risk of extinction - there are so few of them that they might soon be wiped out altogether. Although some plants and animals have always out-competed and replaced others, human activity is changing the world in such a way that many more animals and plants are endangered than would otherwise be.

• Background Extinctions: Extinction has been pervasive throughout Earth history, and every few million years approximately half the species seen in the fossil record either became extinct or had evolved enough new traits to be given new species names. On evolutionary timescales, biodiversity has been maintained by the evolution of new species that replace the extinct species. Rates of extinction have varied among species and through time, but most extinctions are considered “background extinctions”, occurring at rates that did not disrupt entire ecosystems.