Mass extinctions are a widespread and rapid loss of life on Earth, typically in response to some kind of global catastrophe or change in climate. These events have occurred throughout Earth’s history and have played pivotal roles in shaping both its past and current biodiversity.
While they may be best known for destroying life, mass extinctions also promote the evolution of new species, levelling the playing field for groups who, prior to a mass extinction, may have lived in the shadows of more dominant species. Take mammals, for example – they prospered and rapidly diversified after non-avian dinosaurs were wiped out 66 million years ago. There have been five major mass extinction events. Together, these events are known as the ‘big five’.
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What are the five mass extinctions?
The Late Ordovician mass extinction, which took place 445 million years ago (MYA), wiped out 85 per cent of all species. It was the second most destructive event of the ‘big five’ and, unlike the others, may have been triggered by global cooling.
The Late Devonian mass extinction (372–359 MYA) was a drawn-out event that annihilated coral reefs and diverse groups of fish. As much as 70 per cent of all species faced extinction at this time, likely in response to ocean anoxia – a total lack of oxygen.
Next was the End Permian mass extinction (252 MYA) which is best known as the ‘great dying’ – a fitting nickname considering it wiped out 90 per cent of all species. This calamitous event was triggered by the eruption of a huge volcanic system that once lay under what is now Siberia, Russia.
The Triassic-Jurassic mass extinction (201 MYA) was caused by global warming and killed off 75 per cent of all species, including the non-dinosaurian archosaurs. After they disappeared, dinosaurs took their place and established their long-lasting terrestrial dynasty.
This was, of course, toppled during the last of the ‘big five’: the End Cretaceous mass extinction (66 MYA). This was triggered by an asteroid impact and, unlike previous extinctions, erased entire groups of animals and plants almost overnight.
These are just five of the most destructive mass extinction events – according to some estimates, there may have been as many as 20 in the last 540 million years. There’s also growing evidence to suggest that we may be undergoing a sixth mass extinction, as a result of human-induced global warming, making our ‘big five’ a ‘big six’ in the future.
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Top image credit: illustration of pterosaurs flying over a scene of mass destruction. Credit: Getty