An estimated 99% of all species ever living on planet Earth are now extinct. Extinction is part of life’s history, and the extinction of single species happens all the time. Over time lost species are eventually replaced as natural selection acts on the survivors, evolving new species. Mass extinctions in the geological record are defined by the loss of a large part of biodiversity in a (geologically speaking) short interval, like a few hundred to thousands of years.

Paleontologists recognize five big mass extinction events in the fossil record. At the end of the Ordovician, some 443 million years ago, an estimated 86% of all marine species disappeared. At the end of…