Abstract

Mass extinction is when the referee blows the whistle: there is no objective definition of the term. Just as there is no precise discontinuity between background extinctions and mass extinctions, since there have been periods when biodiversity has declined more or less rapidly and profoundly. However, it is accepted to identify five moments when there has been a particularly rapid and drastic decline in species diversity, the last of which was the famous late Cretaceous extinction, 66 million years ago.