(Related story: "'Lost Kingdom' Discovered on Volcanic Island in Indonesia" [February 26, 2006].)
Ken Wohletz, a volcanologist at Los Alamos National Laboratory in New Mexico, said that while the new evidence strongly supports a large volcanic eruption, a space impact can't be ruled out yet.
"Over two-thirds of Earth's surface is covered with water, and because erosion so quickly wipes away evidence of impacts, the knowledge of when large-scale impacts have occurred in the past is still very incomplete," said Wohletz, who was not involved in the study.
To cement their case, volcano advocates will need to find ash layers deposited by the blast, Wohletz said.
William Ryan, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory in New York, believes it is only a matter of time until ash layers are found.
"I suspect we haven't searched adequately, but this paper will start a hunt," Ryan said.
According to written records, the dry fog lingered for just over a year—leaving an indelible mark on human history.
Chinese historians recorded famine events and summer frosts for years after the event.
It was also around this time that a band of Mongolian nomads called the Avars migrated westward toward Europe, where they would eventually establish an empire.
The group may have left home when grasslands that their horses grazed on withered under the darkened skies, historians say.
More controversially, some historians claim that drought caused by the fog contributed to the decline of the Mesoamerican city of Teotihuacan.
(Related story: "New Digs Decoding Mexico's Pyramids of Fire'" [October 21, 2005].)
The spread of bubonic plague throughout Europe and the Middle East, the rise of Islam, and even the fall of the Roman Empire have also been controversially tied to the event.
If a similar volcanic eruption were to occur today, the effects could be just as devastating, experts say.
The reduced sunlight and ashfall would affect agriculture worldwide, and the thick veil of dust and ash could cripple transportation and communication systems.
"Most aircraft cannot fly in [volcanic] dust clouds," Los Alamos's Wohletz said.
"And these dust clouds have a large electrostatic potential that disrupts radio communication."
To make matters worse, there is practically nothing humans can do to prevent such a catastrophe from happening again—or to lessen its effects.
"In today's society, we're no less independent of nature than humankind has ever been," Wohletz said.
"In fact, we might even be more dependent on it."
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