Published online 3 December 2003 | Nature | doi:10.1038/news031201-3


Roast dinosaur off the menu?

Giant meteorite impact 65 million years ago may not have set the world on fire.

Some argue hot meteorite debris could have ignited vegetation wherever it fell to earthSome argue hot meteorite debris could have ignited vegetation wherever it fell to earth© GettyImages

New evidence questions the idea that a meteorite impact thought to have wiped out the dinosaurs triggered worldwide wildfires.

A crater about 180 kilometers wide attests to an asteroid having hit Earth at Chicxulub on the Yucatan Peninsula in Mexico 65 million years ago. But even about 2,000 km from here there were no big fires, claim Claire Belcher of Royal Holloway College in London, UK and her colleagues1. So there can't have been global conflagrations, conclude the researchers.

The group found no charcoal in sedimentary rocks laid down at the time — the end of the Cretaceous period when 85 per cent of all species seem to have become extinct. Other geologists have argued that soot in similar rocks elsewhere is a sign that the meteorite released enough heat to spark fires everywhere.

Traces of the impact have been found in sediments around the world. Rocks from the Cretaceous-Tertiary or K–T boundary contain a sprinkling of the element iridium, believed to have been carried by the meteorite. They are also peppered with tiny glass-like blobs, the frozen remains of molten rock flung high into the air at the impact site.

Some have proposed that this hot debris would have ignited vegetation wherever it fell to earth. Others believe a gigantic fireball, rising over Chicxulub, would have spread hot material over the planet. Either way, widespread wildfires would have helped wipe out life on land.

Charcoal could have been produced only from burnt vegetation, says Belcher's team. So they looked for it in K–T sedimentary rocks across North America, from Colorado in the south to Saskatchewan in the north.

Soot, the researchers argue, could have come from other sources. The particles could have been blown in from afar or produced from oil, coal and gas burnt up at the impact site.

Another possible cause of the mass extinctions is the dust thrown into the atmosphere by the meteorite — it might have blocked out the Sun's heat and light. In other words, the dinosaurs might have frozen, not roasted. 

  • References

    1. Belcher, C.M., Collinson, M.E., Sweet, A.R., Hildebrand, A.R. & Scott, A.C. Fireball passes and nothing burns-The role of thermal radiation in the Cretaceous-Tertiary event: Evidence from the charcoal record of North America. Geology, 31, 1061 - 1064, (2003). | Article | ISI |