In this talk, biologist Anthony Barnosky discusses Earth’s five mass extinctions and whether current species declines may be part of a sixth mass extinction.

Mass extinctions are catastrophic events in which many species become extinct over brief periods of time. The fossil record contains evidence of five mass extinctions, during each of which more than 75% of Earth’s species disappeared. Barnosky describes how scientists use fossil data to determine species extinction rates, and how comparing past and present-day extinction rates can be used to predict the likelihood of another mass extinction. Although many present-day species are threatened, Barnosky argues there is still time to avoid a sixth mass extinction.

This talk is from a 2014 Holiday Lecture Series, Biodiversity in the Age of Humans.