The Holocene extinction, also called "the sixth mass extinction," is the extinction of large numbers of species, ranging from megafauna to microscopic lifeforms, that has been occurring as a result of human activity, particularly the widespread degrading and destruction of highly biodiverse habitats, ranging from coral reefs to tropical rainforests. The vast majority of these extinctions are most likely undocumented because the species have not been discovered by the time of their extinction. The current rate of loss of species may be a hundred to a thousand times the natural extinction (background extinction) rate.