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Anther occurred when the Cretaceous period became the Tertiary about 65 million years ago, when 75 percent of species disappeared. This article is about the first mass extinction at the end of the Ordovician geological period 440 million years ago, when about 86 percent of species were killed.
The fifth one was 65 million years ago, when the dinosaurs vanished. Today we're losing biodiversity at a similar rate. And this is, of course, an anthropogenic mass extinction. The primary cause is human communities. But what we're trying to do in extinction studies is to think about scale in different ways.