When paleontologists refer to the "big five," to what are they referring?

When paleontologists refer to the "Big Five", they are referring to the big five mass extinction events:

-The Ordovician-Silurian extinction events, which happened about 450 million years ago, killing almost 85% of the existing species.

-The Late Devonian extinction, which happened 370 million years ago, finishing more than 80% of the existing species.

-The Permian-Triassic extinction event, which happened 250 million years ago, killing more than 95% of the species of that time.

-The Triassic-Jurassic extinction event, that happened 210 million years ago, ending with almost 76% of the existing species.

-The Cretaceous-Paleogene extinction event, which happened 65 million years ago, ending with more than 75% of the existing species.

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