May 6, 2008 -- The dino-killing Chicxulub meteor might have ignited an oil field rather than forests when it slammed into the Gulf of Mexico 65 million years ago, say geologists.
Smoke-related particles found in sediments formed at the time of the impact are strikingly similar to those created by modern high-temperature coal and oil burning, as opposed to forest fires, says Simon Brassell of Indiana University. He and colleagues from Italy and the U.K. published their report on the discovery in the May issue of the journal Geology.
Evidence of some sort of large burn that perhaps created a global climate change at the end of the Cretaceous has been around since the 1980s. But it has not been settled just what sort of fire it was.
"It seemed like (vegetation) wildfires were the easiest solution," recalled geochemist Wendy Wolbach of DePaul University, who worked on evidence of the fires at the time.
There was even the discovery of a chemical called retene which is released by cone-bearing trees when they burn in forest fires today.
However, that was before the Chicxulub crater had been identified. What's more, Wolbach says, it has never been certain that the fires were global, as some have suggested. For one thing, there has never been a lot of fossil charcoal found from that time, which would be expected if there had been so much vegetation burning.
"There isn't enough charcoal to account for that," said Brassell.
What he and his colleagues have found instead are particles called cenospheres, which resemble the sooty output of industrial coal and oil burning, he told Discovery News. When cenospheres are found, they are usually associated with what's called fly ash, which is manmade.
"In many places the presence of such material is taken as evidence as the presence of human activities," said Brassell.
And since the Cretaceous-Paleogene (a.k.a. Cretaceous-Tertiary) boundary is about 65 million years too early for humans and their coal-fired Industrial Revolution, something else had to be burning fossil fuels.
Brassell and his team suggest that the Chicxulub meteor crashed into oily shales of the Gulf of Mexico, which caused the oil in the rocks to vaporize and ignite in the air, making cenospheres in the process.
Today the large oil fields that edge right up to the Chicxulub structure testify to the ample supply of oil available to burn 65 million years ago. It's even likely the impact itself was responsible for the fracturing and heating of the rocks in that region and allowing the oil to collect into the large pools which are found there today, Brassell explained.
The bottom line, said Wolbach, is that the Chicxulub impact and its aftermath were probably a lot more complicated than it they have sometimes been portrayed.
"The retene seems to suggest that at least some wildfires burned," said Wolbach. "I think it's probably a combination."
Related Links:
Discovery News blog: Earth Impacts