Mass extinction

A mass extinction is a geologically short period in which a large share of all animal species disappears. How many depends on the event; in the largest, it was the majority of marine animals. After that it took millions of years for life to recover, with new species filling the empty places.

How does it work?

Palaeontologists, researchers who study life in the past, read the extinctions from fossils. Rock consists of layers that have been laid down on top of each other over millions of years. The deeper a layer, the older it usually is. If many species disappear at the same time in one layer, that points to an extinction.

Five events count as the largest, the Big Five. They took place about 445, 372, 252, 201 and 66 million years ago. The causes differ. In the largest, at the end of the Permian, gigantic volcanic eruptions that changed the climate and the oceans played a role. In the most recent, at the end of the Cretaceous, the dinosaurs, among others, disappeared after a meteorite impact, reinforced by volcanism.

A tricky question is how fast such an extinction was. Was it a sudden disaster or a gradual decline over a long time? Fossils give only a rough picture, because layers are missing or vary in thickness.

Why it matters

Extinctions show how life responds to major changes, and how it recovers afterwards. That is why researchers compare them with climate and with the oxygen in the oceans.

AI helps to sharpen the picture. A Chinese team trained a model on almost four million fossils, and it suggests that three of the five major extinction events were more gradual than thought (link). Other palaeontologists are more cautious. The model now has to be compared with precise measurements at individual sites.