Mass Extinctions of Earth

Gaurav Kumar

History of Life on Earth Geological Time Spiral
History of Life on Earth Geological Time Spiral USGS (Public Domain/Wikimedia Commons)

Mass extinction can be defined as the rapid reduction in the biodiversity of the planet. The extinction of huge verities of species rapidly is because of catastrophic natural event or changes in the environment that is not possible for adaption by several species. Life on earth has recovered at most five mass extinctions in the last 500 million years that resulted in the extinction of about 99 percent of species from the Earth that ever existed. The occurrence of mass extinction gives rise to the foundation of a new era. When new species evolve to survive under changed circumstances, the old species that are unable to adopt these changes start to extinct (Michael Greshko, 2019).

Mass extinction can also be termed as an abiotic crisis or extinction event and is defined as a rapid reduction in the biodiversity of the environment. It is considered to occur when the extinction rate is much higher than the speciation rate. The fossils of marine species are mostly used to calculate the rate of extinction. It is said that the first major mass extinction event occurred about 2.5 billion years ago and is known as the great oxidation event. After the Cambrian explosion, five further mass extinction occurred on the earth (D.M. Raup and J.J. Sepkoski Jr., 1982).

List of Mass Extinctions

The mass extinctions can be identified in the records of fossils that can be collected from the surface of the earth. There are a total of five mass extinctions in the history of the earth that are enlisted and described below –

1. Ordovician Silurian Extinction – The first mass extinction occurred about 440 million years ago that resulted in the extinction of small marine organisms.

2. Devonian Extinction –The second mass extinction occurred about 365 million years ago that resulted in the extinction of several tropical marine species.

3. Permian-Triassic Extinction – The third mass extinction took place about 250 million years ago and is considered the biggest mass extinction is known in history. It resulted in the extinction of about 90 percent of the vertebrates and marine species.

4. Triassic-Jurassic Extinction – The fourth mass extinction occurred about 210 million years ago that resulted in the extinction of several other vertebrates and land species from earth.

5. Cretaceous-Tertiary Extinction – The fifth mass extinction occurred about 65.5 million years ago that resulted in the extinction of about 75 percent of the species. It is considered that the main cause behind this catastrophic extinction was the meteorite collision.

Causes of Mass Extinction

The most important reason for the mass extinction of earth is the deforestation as well as poaching. Both reasons involve the human act and greed and we can say that the true cause for the extinction of any species is the human. Humans poached various species for their satisfaction and unnecessary fulfillment. Other reasons for mass extinctions include the environmental changes, many species are unable to adapt to the changes that occurred in their surroundings and start to extinct, loss or sudden reduction in their sources of foods, catastrophic climatic or natural disasters. The extinction can also be done by some other world events like the crashing of asteroids or meteorites on the earth’s surface. About 65 million years ago, various species including dinosaurs got extinct when a meteorite of width about 6 miles crashed the earth’s surface (P.R. Ehrlich and A.H. Ehrlich, 1981).

Hence we can say that the major causes of mass extinction can be referred to as the rapid changes in the earth’s atmosphere, ecology, and surface. Several natural occurrences like floods, volcanic eruptions, falling of sea level and collision of asteroids and meteorites are considered the second reason for mass extinction. Global warming, methane eruptions, deforestation, anoxic events, global cooling, poaching of species are also considered as the reasons behind the species extinction.

Here we go again: Earth's major 'mass extinctions'
Graphic on Earth’s “mass extinctions” during the last 500 years

Sixth Mass Extinction

The sixth mass extinction is also known as the Anthropocene extinction or the Holocene extinction and is considered the most serious extinction of civilization because the extinction this time will be permanent. The sixth extinction of species on earth will be much faster as compared to the previous five extinctions that occurred on the earth. For example, the extinction of Mauritius’s Dodo and Russian Steller’s sea cow (G. Ceballos, 2015). In this ongoing extinction, there would be the disappearance of several species like megafauna. According to the researcher’s theory, the over poaching done by humans added much stress to the occurrence of this catastrophic mass extinction in the biodiversity. It is considered that half of the life forms of the Earth would extinct by the year 2100 because of tremendous disruptions caused by humans (Edward Osborne Wilson, 2002).

The main reason to cause sixth extinction is deforestation, global warming, ecological imbalance, and environmental disruptions. All these factors are mainly caused due to unnecessary human activities (J.A. Estes, A. Burdin, and D.F. Doak, 2016).

Prevention Techniques

There are several techniques that could be adapted to avoid the sixth extinction occurrence. We must try to avoid over-exploitation of several natural resources as this is the major reason behind the extinction of several species in the last 50 decades. We also must prevent the natural habitat of rare and important species and also focus on their conservation as well as conservation of their habitat. The importance of practicing afforestation should be taught to each and every human being and also suggest them to reduce the emission of greenhouse gases in the environment. Several camps must be organized in order to create awareness about the significance of the diversity of species to the ecosystem and understand the techniques for preventing our biodiversity (S.L. Pimm et al, 2014).


The mass extinction event has caused a disastrous situation in which several species extinct. In present only 1 to 2 percent living organism is alive and the rest got extinct with time. Natural disasters cannot be controlled however but human actions are also boosting the speed of occurrence of mass extinction on a large scale. This is needed to create awareness among people that their inhuman activities are responsible for these catastrophic events. Poaching of species, deforestation, and emission of greenhouse gases must be controlled.


D. M. Raup, J. J. Sepkoski Jr., Mass extinctions in the marine fossil record. Science 215, 1501–1503 (1982).

Edward Osborne Wilson, “In The Future of Life” , Harvard (2002).

G. Ceballos et al., Accelerated modern human-induced species losses: Entering the sixth mass extinction. Sci. Adv. 1, e1400253 (2015).

G. Ceballos, P. R. Ehrlich, A. H. Ehrlich, The Annihilation of Nature: Human Extinction of Mammals and Birds, (Johns Hopkins Press, Baltimore, MD, 2015).

G. Ceballos, P. R. Ehrlich, Mammal population losses and the extinction crisis. Science 296, 904–907 (2002).

J. A. Estes, A. Burdin, D. F. Doak, Sea otters, kelp forests, and the extinction of Steller’s sea cow. Proc. Natl. Acad. Sci. U.S.A. 113, 880–885 (2016).

Michael Greshko (26 September 2019), “What are mass extinctions, and what causes them?”, accessed on 22nd May 2021, <>

P. R. Ehrlich, A. H. Ehrlich, Extinction: The Causes and Consequences of the Disappearance of Species, (Random House, 1981).

S. L. Pimm et al., The biodiversity of species and their rates of extinction, distribution, and protection. Science 344, 1246752 (2014).


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