The researchers said they believe the liquid carbon rocketed skyward and formed tiny airborne beads that blanketed the planet. The team of U.S., U.K., Italian and New Zealand researchers said those beads, known as carbon cenospheres, cannot be formed through plant matter combustion.

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 Professor Simon Brassell, study co-author and former adviser to lead author Mark Harvey.

The carbon cenospheres were deposited next to a thin layer of the element iridium -- an element more likely to be found in solar system asteroids than on Earth. The iridium-laden dust is believed to be the shattered remains of the approximately 125-mile-wide asteroid's impact.

The study that included Harvey, who is now a geoscientist in New Zealand, Claire Belcher of the University of London and Alessandro Montanari of Italy's Coldigioco Geological Observatory appears in the journal Geology.