Mass Extinction vs Background Extinction
Knowing the difference between mass extinction and background extinction becomes important because they are both categories that come under the umbrella term extinction. Extinction is defined as the irreversible disappearance of an entire species of animal or plant from the Earth. It is important to consider the elimination of an entire species, not just individual members of a species’ population. Extinction is a naturally occurring process. Over the last 3.5 billion years, where life has existed on Earth, many kinds of species have lived and gone extinct. At the present there are about 40 million different species living on Earth, including both animals and plants. However, when compared to the Earth’s history, about 5 billion to 50 billion species have existed so far. Out of those species only about 0.1 % live today, which means 99.9 % of all the species who have ever lived on Earth are now extinct. Extinction is driven by many factors such as geographical changes, certain environmental factors, competitors, lack of food, lack of adaptation to survive in certain environments, etc. Sometimes extinction can happen over a very long period. Nevertheless, sometimes it happens in a flash destroying so many species. Depending on the time that it takes for an entire species to become extinct, the extinction process can be divided into two types: background extinction and mass extinction.
What is Mass Extinction?
Mass extinction happens very quickly and it eliminates hundreds, maybe thousands of species at a time. The causative factors of mass extinction include climate changes, massive and continuous volcanic eruptions, changes in the chemistry of air and water, asteroids or comet strikes, and shifts in Earth’s crust. It is believed that the dinosaurs were entirely wiped out by mass extinction. Mass extinctions are known to be the borderline between two eras in Earth’s history. For example, Cretaceous- Tertiary extinction indicates that mass extinction occurred at the end of Cretaceous period and beginning of the Tertiary period. The biggest and worst mass extinction of all time occurred 251 million years ago at the end of Permian period. Massive volcanic eruption lasting several thousand years caused this mass extinction.
What is Background Extinction?
Background extinction is a process that happen over a very long period. It usually eliminates only one species at a time. It is usually happened by drought, flood, arrival of new competitor species, etc. Usually, fate of a species depends on the ability of surviving and reproducing under different environmental condition where they inhabit. Sometimes certain species go extinct because they gradually change into new species. For example, the currently living North American horse species have evolved from earliest horse species which went extinct millions of years back. Background extinction can also occur suddenly. Usually this happens because the biology of a species cannot adapt quickly to rapid changes in its living habitats (ex: The digestive system of Koalas in Australia is unique among mammals and adapted to feed only on eucalyptus leaves. If sudden climatic changes wiped out eucalyptus forests, Koalas could go extinct suddenly).
What is the difference between Mass Extinction and Background Extinction?
• Background extinction takes very long period to occur, whereas mass extinction takes place in a short period.
• Background extinction usually affects only one species at a time, whereas mass extinction affects many species at a time.
• Unlike the background extinction, mass extinction can change the entire life on Earth.
• Unlike the background extinction, mass extinction is used to denote the borderline between two periods of Earth’s history.
• Mass extinction can occur due to climate changes, massive and continuous volcanic eruptions, changes in the chemistry of air and water, asteroids or comet strikes, and shifts in Earth’s crust, whereas background extinction occurs due to drought, flood, arrival of new competitor species, etc.
Photo By: Marc Dalmulder (CC BY 2.0)