Past, present, and future mass extinctions

Abstract

Enigmatic catastrophic events, involving mass extinction of life forms, have been recorded several times in the Earth history. In many cases, the causes and mechanisms of these major and minor mass extinctions can be traced via the fossil record. A synthesis of the available information is herein made on the major catastrophic events through Earth history to understand the processes in the past and present with speculation into the future. The selective nature of major mass extinctions from the fossil record indicates the vanishing of specific taxa and the survival of others. The sudden extinction of organisms is almost accompanied by a gradual disappearance of other forms, thus excluding any single cause for the killing mechanism. Consequently, the multiple causes’ scenario is the plausible mechanism responsible for the vanishing of biota through the history of the fossil record. On the other hand, the recovery of biota after mass extinctions is also an intriguing phenomenon, in which some groups had rapid recovery whereas others took a long time for a revival. Based on multiple pieces of evidence from Africa, the end Permian extinction and the extinction of some Quaternary megafauna may be related to severe drought. In addition, the current mass extinction is progressively underway; arising from multiple causes and mainly related to anthropogenic activities, widespread diseases, as well as the possibility of extraterrestrial impacts. Reevaluation of the magnitude of the extinction event is urgently needed to judge if these extinctions represent natural episodic fluctuation of the biodiversity curve or unexpected catastrophe. Analyses of invertebrate occurrence data revealed that taxa originated during stressful crises intervals have a wider geographic range size and lower extinction rates. Moreover, species durations, geographic range, and diversity are influencing each other. In addition, the ecological traits of a species may control their extinction pattern and recovery speed-limit. Furthermore, the wide geographical distribution provides potentially to survive mass extinctions. Therefore, narrower geographic-range taxa are facing higher extinction risk.