THE dinosaurs went out with a bang. Most palaeontologists agree that those creatures and much of the rest of Mesozoic life ended when the Earth collided with an asteroid or a comet 65m years ago. But the Mesozoic, too, began with a mass extinction. Some 251m years ago, the efluvia of Siberian volcanoes wiped out 95% of life in the seas, and almost as much on the land, in an episode known as the Great Dying. This was the end of the Permian period, and of the era of life called the Palaeozoic. The survivors regrouped, re-evolved and turned into the Mesozoic species that led eventually to the dinosaurs, pterosaurs, ammonites and belemnites that generations of fossil hunters are familiar with.

How that regrouping happened will be the topic of a presentation by Hugo Bucher, the director of the Palaeontological Institute at the University of Zurich, at the Third International Palaeontological Congress in London on July 3rd. According to Dr Bucher, it occurred faster than anyone had previously thought, but also stuttered on the way as the volcanic activity waxed and waned.

Until now, palaeontologists have thought the recovery took tens of millions of years—a reflection either of the profundity of the Great Dying or of the toxic desert planet that the eruptions created. But that opinion was based on shaky data. Most rock sequences that straddle the end of the Permian are either incomplete or hard to date. Dr Bucher, however, has had the benefit of looking at a set of strata in southern China that were, until recently, off limits to foreign scientists.

These rocks consist of fossil-rich layers containing rapidly evolving marine organisms such as ammonites, interleaved with layers of volcanic ash. The ash contains minerals such as zircon that can be dated precisely from the radioactive decay of some of their components.

The result is 50 reliable time-points in a section that spans 10m years. Previously, the only dateable layers were from the moment the Permian ended and from a subsequent volcanic event some 14m years later. The ages of rocks between these two were little more than guesswork.

Dr Bucher's studies of the Chinese sections indicate two things. First, that there was not one mass extinction at the end of the Permian, but several. Second, the time the recovery took has been greatly overestimated. He says that species such as ammonites and conodonts (primitive eel-like creatures with teeth) had recovered within 1m years of the initial extinction. Another, smaller episode of volcanism 2m years later, which once again heated the planet and turned the seas acid, hammered life again—and again it recovered quickly.

Only two of 15 ammonite families survived this second extinction, says Dr Bucher, but within a million years those two had speciated into 15, and ammonites had regained their former diversity. There also seems to have been a third episode of environmental disruption before conditions stabilised, around 6m years after the initial extinction, and life was left in peace to reconstruct complex ecosystems of the sort that had existed before. Over the next 4m years, habitats that the extinction had eradicated—reefs in the sea and forests on land—re-established themselves, albeit with entirely novel species. To quote Voltaire, then, “Le malheur des uns fait le bonheur des autres.”