Several mass extinctions are recorded in the fossil record. Paleontologists have been able to recognize patterns within and between extinction events. Currently, there are five major extinction patterns recognized. Steven M. Stanley, has outlined them in his book entitled, Extinction.
- Extinction strikes in both the land and the sea.
- On the land, while animals suffer repeatedly,
plants tend to be highly resistant to mass extinctions.
- Preferential disappearance of tropical forms of life
during mass extinctions.
- Tendency of certain groups of animals to experience
them repeatedly (for example, trilobites and ammonoids).
- Alleged equal spacing, or periodicity in geological time
(occurring about every 26 million years).
These similarities between distinct extinction occurrences aid paleontologists
in determining the agents that perpetuated the disappearances of species in each
extinction event. Such agents are currently divided into two types:
- Catastrophic Agents- such as meteorite impacts and
- Earth Agents- such as volcanism, glaciation, variations
in sea level, global climatic changes, and changes in ocean
levels of oxygen or salinity
Although these agents can explain mass extinction, the causes of mass extinction events remains relatively unknown.
The Vendian Mass Extinction
Mass Extinctions of the Phanerozoic Menu