Charred to extinction

if a team of oceanographers are to be believed, methane-fuelled firestorms could have been the last straw for some species, including the dinosaurs. They believe that the impact of a giant asteroid or comet in the Gulf of Mexico released vast quantities of methane that set the air on fire and hastened the extinction of several life forms.

About 65 million years ago, huge amounts of methane generated by rotting vegetation lay trapped in sediments more than 500 metres below the sea level. At these depths, low temperatures and high pressure allow methane to combine with water to form solid methane hydrates.

Several countries, including the us , Germany and Japan are keen on exploiting the potential of methane hydrates as fossil fuels.The methane hydrate reserves have already played a critical role in the Earth's history millions of years ago, believes Burton Hurdle and his colleagues of the Naval Research Laboratory in Washington, usa.

As the asteroid or comet hit the ocean floor, huge shock waves were generated, which travelled round the planet and unleashed enormous amounts of trapped methane. The methane could have been ignited by streaks of lightning in the charged atmosphere. "The atmosphere itself would have been on fire," says Burton. "This could have led to the demise of dinosaurs," he surmises (New Scientist , Vol 164, No 2213.

The researchers cite more evidence for their theory. Earlier, a discovery at Black Ridge off the coast of Florida also showed disruption in sediments of the Cretaceous period (65 million years ago), possibly due to methane release. Of late, researchers have also found that trapped methane often escapes from the sea floor even in the absence of asteroid strikes.

Dick Norris, a palaeo-biologist at Woods Hole Oceanographic Institution in Massachusetts, usa, who was involved in the discovery of the Black Ridge sediments, agrees with Hurdle and his colleagues. A lot of methane could have been released from the site if it had been trapped in the form of methane hydrate, he says, adding that increased preponderance of the isotope carbon-12 over carbon-13 immediately after the impact suggests that a lot of methane was burnt. However, this pattern is not repeated all over the globe.

Some experts are cautious of accepting the new theory. Peter Schultz of Brown University in Providence, Rhode Island, usa , who has studied the late Cretaceous impact, says, "I think the idea would be intriguing, but I'm not sure if an impact, even this big, would have liberated that amount of methane."

However, Angela Milner, head of vertebrate paleontology at the Natural History Museum in London, believes that the population of dinosaurs were shrinking even before the collision. And the huge methane fires could have hurried their demise.