Based on a Indiana University news release
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This
painting depicts an asteroid slamming into tropical, shallow seas of
the sulfur-rich Yucatan Peninsula in what is today southeast Mexico.
The aftermath of this immense asteroid collision, which occurred
approximately 65 million years ago, is believed to have caused the
extinction of the dinosaurs and many other species on Earth.
Credit: Donald E. Davis
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The asteroid presumed to have wiped out the dinosaurs
struck the Earth with such force that carbon deep in the Earth's crust
liquefied, rocketed skyward, and formed tiny airborne beads that
blanketed the planet, say scientists from the U.S., U.K., Italy, and
New Zealand in this month's Geology.
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-million-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," said Indiana University
Bloomington geologist Simon Brassell, study coauthor and former adviser
to the paper's lead author, Mark Harvey.
The carbon cenospheres
were deposited 65 million years ago next to a thin layer of the element
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-km-wide asteroid's impact. Like the
iridium layer, the carbon cenospheres are apparently common. They've
been found in Canada, Spain, Denmark and New Zealand.
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The
painting titled "K/T Hit" by artist Donald E. Davis. This impact
occured 65 million years ago, coinciding with the the dinosaur
extinctions.
Credit: Donald E. Davis
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But the cenospheres' origin presented a double 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. Equally
baffling, there were no power plants burning coal or crude oil 65
million years ago, and natural burial processes affecting organic
matter from even older ages -- such as coals from the
300-million-year-old Carboniferous Period -- had simply not been cooked
long or hot enough.
"Carbon cenospheres are a classic indicator
of industrial activity," Harvey said. "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 new
process, the violent pulverization of the Earth's carbon-rich crust.
Geologists
do believe the Earth burned in spots as molten rock and super-hot ash
fell out of the sky and onto flammable plant matter. But the
charcoal-ized 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
was ash from global scale forest fires, but the present research
strongly contradicts that assumption.
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Carbon
cenospheres are tiny, carbon-rich particles that form when coal and
heavy fuel are heated intensely. Scientists have now learned that
cenospheres can form in the wake of asteroid impacts, too.
Credit: Mark Harvey / Indiana University
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The
scientists examined rock samples from eight marine locations in New
Zealand, Italy, Denmark and Spain. They also examined carbon-rich
particles from five non-marine locations in the U.S. and Canada.
Following chemical and microscopic analysis, the researchers concluded
the particles were carbon cenospheres, similar to the ones produced by
industrial combustion.
The scientists also found that the farther the sample site was from the Chicxulub
Crater, the smaller the cenospheres tended to be. That observation is
consistent with the expectation that particles were produced by the
asteroid impact, since once the particles are ejected, heavier
particles should fall back to Earth sooner (and travel shorter
distances) than lighter particles.
Last, the scientists
estimated the total mass of carbon cenospheres ejected by the asteroid
collision, assuming a global distribution, to be perhaps as much as 900
quadrillion kilograms. Whether or not the carbon cenospheres are truly
ubiquitous, however, needs further corroboration.
"There are
still clues to unravel about the events occurring around the time of
the impact," Brassell said. "And there are aspects of the Earth's
natural carbon cycle that we didn't previously consider."
Harvey
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."
Harvey conducted the research while he was a master's
student at IU Bloomington. He is now a geoscientist for Sinclair Knight
Merz in New Zealand. Claire Belcher (University of London) and
Alessandro Montanari (Coldigioco Geological Observatory) also
contributed to the study. It was funded by the Geological Society of
America, the Indiana University Department of Geological Sciences, and
the Society for Organic Petrology.
Copyright: Astrobiology Magazine
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