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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 18 Dec 2013 09:21:13 -0800 (PST)
Message-ID: <201312181721.rBIHLDth017697_at_zagami.jpl.nasa.gov>


Why Halley's Comet May Be Linked to Famine 1,500 Years Ago
By Mike Wall
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

"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

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.
Received on Wed 18 Dec 2013 12:21:13 PM PST

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