June 14, 2008
More Revelations on Dinosaur Extinction
ASTEROIDS The asteroid presumed to have wiped out the dinosaurs struck the Earth with such force that carbon deep in the planet's crust liquified, rocketed skyward, and formed tiny airborne beads that blanketed the planet, say scientists from the U.S., U.K., Italy, and New Zealand.
The beads, known to geologists as carbon cenospheres, cannot be formed through the combustion of plant matter, contradicting a hypothesis that the cenospheres are the charred remains of an Earth on fire. If confirmed, the discovery suggests environmental circumstances accompanying the 65,000,000-year-old extinction event were slightly less dramatic than previously thought. "Carbon embedded in the rocks was vaporized by the impact, eventually forming new carbon structures in the atmosphere," explains geoscientist Simon Brassell of Sinclair Knight Merz in New Zealand.
The carbon cenospheres were deposited next to a thin layer of iridium -an element more likely to be found in solar system asteroids than in the Earth's crust. The iridium-laden dust is believed to be the shattered remains of the 200-kilometer-wide asteroid's impact. Like the iridium layer, the carbon cenospheres apparently are common. They have been found in Canada, Spain, Denmark, and New Zealand.
However, the cenospheres' origin presented a mystery. The cenospheres had been known to geologists only as a sign of modern times; they form during the intense combustion of coal and crude oil. Obviously, there were no power plants in operation millions of years ago, and natural burial processes affecting organic matter from even older ages-such as coals from the 300,000,000-yearold Carboniferous Period-simply had not been cooked long or hot enough.
"Carbon cenospheres are a classic indicator of industrial activity," Brassell points out. "The first appearance of the carbon cenospheres defines the onset of the Industrial Revolution." The scientists concluded the cenospheres could have been created by a different process, the violent pulverization of the Earth's carbonrich crust.
Geologists do believe the Earth burned in spots as molten rock and super-hot ash fell out of the sky onto flammable plant matter, but the charcoalized products of these fires only appear in some places on Earth, and are more often found near the asteroid impact site of Chicxulub Crater, just west of Mexico's Yucatan Peninsula. Some geologists had thought all carbon particles resulting from the impact were ash from global-scale forest fires, but the present research strongly contradicts that assumption.