How fossil fuels killed the dinosaurs

Research from a team headed by New Zealand geologist Mark Harvey has overturned assumptions about the giant asteroid which is believed to have wiped out dinosaurs 65 million years ago.

The research, done by the Aucklander while he was studying for a masters degree in geology at Indiana University, was published today in the international scientific journal Geology.

Mr Harvey said the asteroid did not need to start forest fires around the world to achieve the extinction.

Instead, he said the asteroid hit oil or coal deposits when its impact made the 200km-wide Chicxulub Crater, just west of Mexico's Yucatan Peninsula.

It struck with such force that the buried carbon liquefied, rocketed skyward, and formed tiny airborne beads that blanketed the planet in soot.

The "KT boundary" between the Cretaceous and Tertiary epochs 65 million years ago is identified by a couple of key markers in the geological record -- a layer of a mineral called iridium which is rare on Earth's surface but more common in asteroids, and a layer of soot.

Until now many geologists thought the carbon particles resulting from the impact was ash from global forest fires, but Mr Harvey's research has overturned turned that assumption.

Mr Harvey, now a scientist for Sinclair Knight Merz engineering consultancy and working on geothermal energy, is the lead author for a team of researchers from Britain, the United States and Italy.

With other scientists, he examined carbon in rock samples from eight marine sediments in New Zealand, Italy, Denmark and Spain, and carbon-rich particles from five non-marine locations in the US and Canada.

They found some of the particles among the soot were carbon "cenospheres", tiny beads similar to the ones produced by intense industrial combustion -- but there were no power plants burning coal or oil 65 million years ago.

"Carbon cenospheres are a classic indicator of industrial activity," Mr Harvey said. "The first appearance of the carbon cenospheres defines the onset of the industrial revolution."

Some burned vegetation has been found in the layer close to the impact site, but scientists think these fires broke out as molten rock and super-hot ash fell out of the sky and onto forests.

Researchers have previously suggested there were mass extinctions as global forest fires pumped enough carbon dioxide into the atmosphere to cause a period of runaway global warming, or they spewed enough soot to block out the sun and kill off the plants on which herbivorous dinosaurs fed, starving the meat-eaters further up the food chain.

Mr Harvey's team found that the cenospheres became smaller the further the sample site was from the Chicxulub Crater -- consistent with the heavier particles produced by the asteroid impact falling to earth sooner than lighter particles.

The scientists also estimated the total mass of carbon cenospheres ejected by the asteroid collision to be 900 billion tonnes.

Mr Harvey -- who also has a degree in biology from Auckland -- is interested in the unique properties of the cenospheres themselves.

"Perhaps we can generate and study carbon cenospheres to better understand them," he said. "We also need to look for the cenospheres in other parts of the world and also around the time of other extinction events."

- NZPA