Earth has seen five mass extinctions, each of which wiped off a considerable amount of the planet's species.
The first mass extinction happened 443 million years ago, near the conclusion of the Ordovician period.
The second great extinction happened near the conclusion of the Devonian period, approximately 375 million years ago.
The third mass extinction happened 252 million years ago, near the conclusion of the Permian period.
The fourth mass extinction occurred near the conclusion of the Triassic period, approximately 201 million years ago.
The sixth mass extinction happened around 66 million years ago towards the conclusion of the Cretaceous period.
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