Dinosaurs were wiped out in giant firestorm when meteor ignited methane, say scientists

THE DEMISE OF the dinosaurs may have been caused by a global firestorm, when methane was released from under the sea by a meteorite impact, American researchers say.

The death of the dinosaurs is usually pegged to a period 65 million years ago, when a huge meteorite hit what is now the Gulf of Mexico. According toBurton Hurdle, of the Naval Research Laboratory in Washington DC, there were at the time huge amounts of methane, generated by rotting vegetation, trapped in sediments as much as 500 metres below sea level.

He and his colleagues suggest that when the meteorite, reckoned to have been between 100 and 160km wide and travelling at about 32,000kmh, smashed into the Yucatan peninsula in Mexico, it generated shock waves that would have been transmitted around the world and shaken up the sediments - releasing the methane into the atmosphere.

In today's New Scientist magazine, Dr Hurdle and his colleagues suggest that the gas could then have been ignited by lightning, sparking a worldwide firestorm.

According to Dr Hurdle, "the atmosphere itself would have been on fire".

Dick Norris, an expert in fossil biology at the Woods Hole Oceanographic Institution in Massachusetts, said some of the fossil record suggests large amounts of methane were burnt at the time. But, he pointed out, the evidence suggeststhe effect was not worldwide.

A British expert on the demise of the dinosaurs was less enthusiastic. Dr Angela Milner of the Natural History Museum in London said: "The idea of huge methane fires doesn't accord with what we know from the fossil record. It doesn't explain, in particular, why so many animal groups did survive. The question of why they did is one which catastrophe theories haven't adequately answered in trying to explain why the dinosaurs died out."

In research published in 1997, Dr Milner and colleagues at the museum showed that by the time the meteorite hit, the dinosaurs had been in a gradual decline for about eight million years. "We think that was due to climate change and the consequent changes in habitat," Dr Milner said yesterday. "Marshy conditions were breaking up the dinosaurs' previous habitats."

Other experts on methane deposits were also unsure of Dr Hurdle's hypothesis. "It's intriguing, but I'm not sure even a meteorite impact this big would have liberated that amount of methane," said Peter Schultz of Brown University, Rhode Island.

Competing Theories

A meteorite 100 to 160km across crashed into Mexico 65 million years ago, causing radical weather changes. Fossil data confirm impact.

Dinosaurs had been in long-term decline, with many species dying off for the previous eight million years due to climate change sparked by continental drift. Sea-level data confirmed by fossil record.

Volcanic eruptions led to global cooling; dinosaurs unable to cope. This idea is strengthened by geological data showing that some volcanic eruptions lasted a million years.

"Genetic exhaustion" - the dinosaurs had ceased to be able to evolve to cope with any sort of exterior change. Hard to confirm, as there is no DNA to compare between different epochs.

A global methane firestorm triggered by the meteorite impact toasted them all. Does not yet explain how early mammals - our ancestors - survived.