Mass Extinctions and Their Aftermath, A. Hallam, P. B. Wignall, Oxford University Press, 1997, ISBN 978-0-19-854916-1, ... He defines mass extinction as any substantial increase in the amount of extinction (that is, lineage termination) suffered by more than one geographically widespread higher taxon during a relatively short interval of geological time, resulting in at least temporary decline in their standing diversity ... more concise one offered here is that a mass extinction is an extinction of a significant proportion of the world's biota in a geologically insignificant period of time ...
