Historically, Earth encountered five events – the so-called “big five” – mass extinction phenomena, namely the Ordovician event (∼443 million years ago), the Devonian event (∼359 million years ago), the Permian event (∼251 million years ago), the Triassic event (∼200 million years ago) and the Cretaceus event (∼65 million years ago). Following each of these events, at least 75% of species present at the time had disappeared.