THE dinosaurs, as every schoolchild knows, died out 66m years ago, at the end of the Cretaceous period. But there is an argument about whether they went with a bang or a whimper. The bang brigade blame an asteroid that hit Earth at exactly the right time (the crater it created is in southern Mexico). This would have caused fires around the planet and thrown up a dust cloud that may have obscured the sun for decades. The whimperers blame a longer period of ecological stress—the result of huge volcanic eruptions in what is now India poisoning the atmosphere.

Some people think both were needed to push life over the edge (it was not only dinosaurs; a large fraction of other animal species succumbed, too). But one possibility has never been nailed down. This is that the impact actually caused the eruptions. That is the thesis of Paul Renne of the University of California, Berkeley, and his colleagues. And in this week’s Science they publish a plethora of data on rocks from the period to back that thesis up.

The data in question are the precise ages of successive layers of lava in the Deccan Traps, as the volcanic province created by the Cretaceous eruptions is known (see photograph and map). The researchers measured, in many layers of these rocks, the amount of an isotope of argon that had been created by the decay of radioactive potassium therein since those rocks had solidified. The half-life of this decay process is known with great accuracy, so rocks can be dated precisely using it.

The dates Dr Renne came up with showed that, though the fissure through which the Deccan lava was erupting was already open when the asteroid arrived, the rate of eruption accelerated markedly within 50,000 years (a geological eyeblink) of that arrival. Dr Renne thinks the impact’s shock waves shook the Earth so violently that they rearranged the subterranean plumbing which fed the fissure, causing this acceleration. The eruptions then raged on for half a million years. Only when they ceased did life start to recover. In the case of the dinosaurs, new data have thus firmed up the timing of a coincidence that was previously only suspected. But another paper, pertaining to an earlier mass extinction, has done exactly the opposite: it has undermined the case for a coincidence in which almost all palaeontologists had until now believed. The extinction in question happened at the end of the Permian period, 251.9m years ago, according to many independent datings of oceanic rocks from the time. Just as the Cretaceous extinction cleared the board for the mammals, so the Permian one cleared it for the dinosaurs. Like the end of the Cretaceous, this was an epoch of extensive volcanism (this time, in what is modern Siberia), though no clear sign of an impact has been found. What was assumed to be clear, though, was that, as happened in the Cretaceous, life on land and life at sea were hit at the same time. But a paper to be published this month in Geology, by Robert Gastaldo of Colby College, in Maine, begs to differ. Dr Gastaldo thinks extinctions on land began long before those at sea. Once again, the new interpretation relies on the precise dating of rocks. The rocks in question are from a layer of volcanic ash in the otherwise sedimentary Karoo basin, in South Africa. The Karoo is a part of the world where the transition from the lush conditions of the late Permian to the dry ones of the early Triassic, which followed it, seemed starkly clear—as did the shift in species. That climatic change is reckoned to be part of what caused the mass extinction.

In fact, according to Dr Gastaldo’s specimens, the transition was anything but stark. He found “Permian” animals in rocks thought Triassic, and pollen from “Triassic” plants in Permian layers. Date-wise, the whole thing looked a mess. The ash layer, though, marked the moment when a well-known group of Permian animals, the dicynodonts, started to disappear.

Dr Gastaldo asked Sandra Kamo, a geochronologist, to date this layer. She found, by plotting the decay of radioactive uranium into lead, that it is 253.5m years old. It was thus deposited more than 1.5m years before the Siberian eruptions started and the extinction in the oceans began. How the Permian really ended, and how long the extinction took, has therefore become even more mysterious than before.