The Major Extinction Events

Time of Extinction

Era Period Epoch Duration* Extinction Event Event

Cenozoic

Mesozoic

Paleozoic

Quaternary Tertiary

Cretaceous

Jurassic

Triassic

Permian

(Carboniferous)

Pennsylvanian

(Carboniferous)

Mississippian

Devonian

Silurian

Ordovician

Cambrian

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Precambrian

57.8-66.4 66.4-144 144-208 208-245 245-286

286-325

325-360 360-408 408-438 438-505 505-570 570-4500

Sixth

Fifth

Fourth Third

Second First

* Approximate time in millions of years before present

Source: Center for Biodiversity and Conservation. 1999. Humans and Other Catastrophes: Perspectives on Extinction. New York: Center for Biodiversity and Conservation, American Museum of Natural History, p. 5. (Reprinted with permission)

Each of the first five extinctions represents a significant loss of biodiversity. The recovery from these extinctions has always been relatively good. It appears that the extinctions were followed by a sudden burst of evolutionary diversification on the part of the remaining species, presumably because these survivors started using habitats and resources that had previously been occupied by more competitively successful species that had gone extinct. However, this does not mean that the recovery from mass extinction was rapid; it has usually required some tens of millions of years (Jablonski, 1995).

It has been hypothesized that we are currently on the brink of a sixth mass extinction. However, this sixth extinction differs in a number of ways from previous events. The five other mass extinctions predated humans and were probably the products of some physical process (perhaps climate change as a result of meteor impacts) rather than the direct consequence of the action of some other species. In contrast, the sixth extinction is human-induced. Consequently, unlike previous events, the most recent extinction event can be slowed or reversed.

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