It is unlikely the dinosaurs perished in a global firestorm triggered by the asteroid strike on Earth 65 million years ago, scientists have claimed. A popular theory suggests the impact, which was centred on Chicxulub in Mexico, generated enough energy to set off a raging worldwide inferno. But a new study shows rocks laid down at the time contain little charcoal - a possible tell-tale record of fires. The researchers have published details of their work in the journal Geology. The wildfires theory had grown up from previous research. One study had even found evidence of soot in rocks from around the Earth dating to the time of the impact. It is thought that in addition to the devastation these fires caused, the soot thrown up into the atmosphere as a result of the cataclysmic event may have helped block sunlight, causing global cooling and a shut-down of photosynthesis. Plants not consumed in the inferno would have just shrivelled away - so the theory goes. But now Claire Belcher, of Royal Holloway, University of London in Egham, has come forward with research that challenges this particular view of dinosaur Armageddon.

She studied six sites in a transect through the western interior of North America. Each site dates to the end of the Cretaceous Period when the impact occurred. Each of these sites records a geological boundary dividing the end of the Cretaceous period from the beginning of the Tertiary. This Cretaceous-Tertiary boundary, or K-T boundary, marks the extinction of the dinosaurs and is thought to be associated with the impact of a large space object because the sedimentary rocks of this layer contain large quantities of the element iridium, which is most commonly found in meteorites.

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