[meteorite-list] Why Halley's Comet May Be Linked to Famine 1, 500 Years Ago

[Ron Baalke]

http://www.space.com/24005-halleys-comet-linked-to-ancient-famine.html 

Why Halley's Comet May Be Linked to Famine 1,500 Years Ago
By Mike Wall
space.com
December 18, 2013
 
SAN FRANCISCO - The ancients had ample reason to view comets as harbingers 
of doom, it would appear.

A piece of the famous Halley's comet likely slammed into Earth in A.D. 
536, blasting so much dust into the atmosphere that the planet cooled 
considerably, a new study suggests. This dramatic climate shift is linked 
to drought and famine around the world, which may have made humanity more 
susceptible to "Justinian's plague" in A.D. 541-542 - the first recorded 
emergence of the Black Death in Europe.

The new results come from an analysis of Greenland ice that was laid down 
between A.D. 533 and 540. The ice cores record large amounts of atmospheric 
dust during this seven-year period, not all of it originating on Earth. 

"I have all this extraterrestrial stuff in my ice core," study leader 
Dallas Abbott, of Columbia University's Lamont-Doherty Earth Observatory, 
told LiveScience here last week at the annual meeting of the American 
Geophysical Union.

Certain characteristics, such as high levels of tin, identify a comet 
as the origin of the alien dust, Abbott said. And the stuff was deposited 
during the Northern Hemisphere spring, suggesting that it came from the 
Eta Aquarid meteor shower - material shed by Halley's comet that Earth 
plows through every April-May.

The Eta Aquarid dust may be responsible for a period of mild cooling in 
533, Abbott said, but it alone cannot explain the global dimming event 
of 536-537, during which the planet may have cooled by as much as 5.4 
degrees Fahrenheit (3 degrees Celsius). For that, something more dramatic 
is required.

Ice core data record evidence of a volcanic eruption in 536, but it almost 
certainly wasn't big enough to change the climate so dramatically, Abbott 
said.

"There was, I think, a small volcanic effect," she said. "But I think 
the major thing is that something hit the ocean."

She and her colleagues have found circumstantial evidence of such an impact. 
The Greenland ice cores contain fossils of tiny tropical marine organisms 
- specifically, certain species of diatoms and silicoflagellates.

An extraterrestrial impact in the tropical ocean likely blasted these 
little low-latitude organisms all the way to chilly Greenland, researchers 
said. And Abbott believes the object responsible was once a piece of Halley's 
comet.

Halley zooms by Earth once every 76 years or so. It appeared in Earth's 
skies in A.D. 530 and was astonishingly bright at the time, Abbott said. 
(In fact, observations of Halley's comet go way back, with research suggesting 
the ancient Greeks saw the comet streaking across their skies in 466 B.C.)

"Of the two brightest apparitions of Comet Halley, one of them is in 530," 
Abbott said. "Comets are normally these dirty snowballs, but when they're 
breaking up or they're shedding lots of debris, then that outer layer 
of dark stuff goes away, and so the comet looks brighter."

It's unclear where exactly the putative comet chunk hit Earth or how big 
it was, she added. However, a 2004 study estimated that a comet fragment 
just 2,000 feet (600 meters) wide could have caused the 536-537 cooling 
event if it exploded in the atmosphere and its constituent dust were spread 
evenly around the globe.