Earth has had five mass extinction events in the last 540 million years, in which more than three-quarters of animal species went extinct. We're on the verge of the sixth mass extinction, but it's not too late to stop it.
About 250 million years ago, the world suffered through an extinction event that makes the death of the dinosaurs look like a minor hiccup by comparison. And now we have our best understanding yet of what caused the Great Dying.
375 million years ago, Earth suffered through its worst extinction event ever: 95% of all species perished. But here's the paradox: extinctions weren't actually any more common then than they are now. The real secret is that Earth's biodiversity collapsed.