Mass extinction
Some 90 per cent of species that
have ever lived on earth have vanished from the planet. But
extinction is not just confined to history; it's believed that
we're experiencing another wave of mass extinction right now: the
Holocene extinction event.
At a glance
Extinction has been happening since the dawn of time. It occurs for many different reasons: destruction of habitat by the elements, for example, or relentless hunting by hungry predators.
It's generally agreed that there have been five major extinction events during the last 550 million years. The Ordovician extinction event is dated around 438 million years ago and may have been caused by the onset of an ice age. Most of earth's complex life forms lived in the seas, and the change in temperature destroyed many of their natural habitats. This event led to around a quarter of marine families being wiped out.
The Devonian extinction occurred some 360 million years ago and also saw a quarter of marine families becoming extinct, including much of the world's coral reefs. Its causes are unclear.
The Permian extinction is also known as 'The Great Dying'. It occurred 245 million years ago when 95 per cent of all species became extinct. The causes of this are thought to be volcanic activity, asteroid impact, or severe global warming, which reduced oxygen levels in the oceans to virtually nil.
The Triassic extinction is also thought to have been partly prompted by volcanic activity and occurred about 208 million years ago. It accounted for the disappearance of around half of the species on the planet, and opened the door for the era of the dinosaurs.
The Cretaceous extinction was the last of its kind until relatively modern times and accounted for the disappearance of the dinosaurs. It is thought to have been caused by a huge asteroid, some 180km in diameter, that hit the earth around 65 million years ago in what is now southern Mexico.
At a glance
Extinction has been happening since the dawn of time. It occurs for many different reasons: destruction of habitat by the elements, for example, or relentless hunting by hungry predators.
It's generally agreed that there have been five major extinction events during the last 550 million years. The Ordovician extinction event is dated around 438 million years ago and may have been caused by the onset of an ice age. Most of earth's complex life forms lived in the seas, and the change in temperature destroyed many of their natural habitats. This event led to around a quarter of marine families being wiped out.
The Devonian extinction occurred some 360 million years ago and also saw a quarter of marine families becoming extinct, including much of the world's coral reefs. Its causes are unclear.
The Permian extinction is also known as 'The Great Dying'. It occurred 245 million years ago when 95 per cent of all species became extinct. The causes of this are thought to be volcanic activity, asteroid impact, or severe global warming, which reduced oxygen levels in the oceans to virtually nil.
The Triassic extinction is also thought to have been partly prompted by volcanic activity and occurred about 208 million years ago. It accounted for the disappearance of around half of the species on the planet, and opened the door for the era of the dinosaurs.
The Cretaceous extinction was the last of its kind until relatively modern times and accounted for the disappearance of the dinosaurs. It is thought to have been caused by a huge asteroid, some 180km in diameter, that hit the earth around 65 million years ago in what is now southern Mexico.
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