At the end of the Ordovician, some 444 million years ago, the oceans emptied out. Something like eighty-five percent of marine species died off. For a long time, the event was regarded as one of those pseudo-catastrophes that just went to show how little the fossil record could be trusted. Today, it’s seen as the first of the Big Five extinctions, and it’s thought to have taken place in two brief, intensely deadly pulses.
