THE dinosaurs, famously, went out with a bang. Some 65.5m years ago, at the end of the Cretaceous period, the Earth collided with an asteroid and the biggest terrestrial beasts in history were no more. That left things clear for the rise of the mammals. But how did the dinosaurs rise to power in the first place? Some light on this question has just been shed by a paper published in Science by Micha Ruhl of Utrecht University, in the Netherlands, and his colleagues.

Dinosaurs first appear in the fossil record during the Triassic period, some 230m years ago. They do not take over, though, until the end of the Triassic, 201m years ago. That date marks one of five recognised mass extinctions in history (the end of the Cretaceous was another). In it, half the world's known species disappeared.

Until now, the end of the Triassic has been blamed on massive volcanic eruptions that went on for 600,000 years. Dr Ruhl, however, reckons that was not the cause—or, at least, not directly.

By analysing the isotopic composition of hydrocarbon molecules from plant waxes of the period, he found what looks like a spike in the amount of recently non-biological carbon (which has a distinctive ratio of light isotopes to heavy ones), lasting between 10,000 and 20,000 years. He thinks the liberation of methane stored at the bottom of the ocean in structures called clathrates is the most likely culprit. The alternative, that the carbon came from the volcanoes, is unlikely because the spike is much shorter than the period of volcanic activity. Methane is a greenhouse gas far stronger than carbon dioxide, so the consequence would have been a rapid warming of the climate—a phenomenon that the rocks suggest did actually happen.

This is not the first time a methane burp has been blamed for an extinction. Though the Cretaceous asteroid cleared the stage, mammals did not really get going until 10m years later, in the Eocene epoch. The preceding Palaeocene epoch was also brought to an end, the rocks suggest, by a sudden release of methane.

The burp could, of course, have been provoked by the eruptions, so the volcanoes are not off the hook completely. But, for those of a nervous disposition, the tying of an ancient greenhouse warming to an ancient mass extinction might suggest lessons for the future.