[WoofDog123]

As you undoubtedly know, there is further speculation based on tree rings and I am not sure what else that a meteor/comet event around 540ad caused total collapse of some social/governing institutions in europe (e.g. the remaining roman institutions), IIRC there is textual reference to it raining mud or something otherwise exotic in ?france or somewhere western europe.

[SunkenCiv]

Small but deadly comets identified
by Damian Carrington
Thursday, September 16, 1999

Dr Matt Genge, from London's Natural History Museum... identifies comets between just 50 to 100 metres wide as the most terrifyingly destructive, with massive heat and shock waves burning people and crushing buildings... A 60-metre-wide comet exploded over Siberia in 1908 with 600 times the energy of the bomb dropped on Hiroshima. It laid waste to a 40-km-wide patch of forest, but, fortunately, the area was unpopulated. However, comets of this size are expected to strike the Earth every 100 to 300 years. If the 1908 comet had arrived just eight hours earlier, it would have struck London, killing everything as Dr Genge described... Ironically, it is because the 50 to 100-metre-wide comets are so weak that they are so dangerous. They break up into fragments which explode just a few kilometres above the ground - "the optimum altitude for maximum devastation", said Dr Genge.

There's a view that the dark ages were literally dark (didn't check these old links):

Ancient myths, tree rings point to giant comet's visit to Earth

Ancient Myths And Tree Rings Point To Giant Comet's Visit To Earth

Tree rings challenge history
by BBC News Online's Jonathan Amos

Mike Baillie, professor of palaeoecology at Queen's University in Belfast, UK, said it was very clear from the narrowness of growth rings in bog oaks and archaeological timbers that a great catastrophe struck the Earth in AD 540. He said mythical stories certainly seemed to point to a comet striking the Earth at about the right time. He said King Arthur died in this period and some stories talk about long arms in the sky delivering mighty blows. Professor Baillie said chemical analysis would be carried out on the tree rings to investigate the comet idea further. He hopes also to get access to ice cores to see if they record any interesting data that might support the comet theory.

Tree Rings Hint At Dark Ages Mystery [MSNBC, not sure we can use those, so excerpt removed]

The 536 AD Dust-Veil Event
by William R. Corliss

"There are two possibilities: a huge volcanic eruption or a collision between the Earth and a solid object: an asteroid or comet. Ice-cores drilled from Greenland show no evidence of large-scale volcanic activity at that time, so Professor Baillie and others now believe a cosmic impact is more likely. The result would have been to throw up a huge veil of dust and debris, cooling the Earth and producing widespread crop failures."

This was put forward in 1994. David Keys' book which attributes it to a volcanic eruption (Keys is a journalist, not a scientist) is just a couple of years old. For more links, click the link after "in reply to" (beginning of this message) to see an earlier post on this topic.

[my comment from 2000] I still haven't read it, but have bought it. I've heard plenty about it and have been interested in it for some time. During a search for "dark ages" and "asteroid" I found a page by some real crank that discusses it, and attributes to Keys the idea that an eruption of Krakatoa was responsible. Previously I'd heard only about an NE Eurasian impact as the source of these literally "dark ages".

Catastrophe: A Quest for the Origins of the Modern World by David Keys

It was a catastrophe without precedent in recorded history: for months on end, starting in A.D. 535, a strange, dusky haze robbed much of the earth of normal sunlight. Keys's narrative circles the globe as he identifies the eerie fallout from the months of darkness: unprecedented drought in Central America, a strange yellow dust drifting like snow over eastern Asia, prolonged famine, and the hideous pandemic of the bubonic plague. With a superb command of ancient literatures and historical records, Keys makes hitherto unrecognized connections between the "wasteland" that overspread the British countryside and the fall of the great pyramid-building Teotihuacan civilization in Mexico, between a little-known "Jewish empire" in Eastern Europe and the rise of the Japanese nation-state, between storms in France and pestilence in Ireland. In this fascinating, groundbreaking, totally accessible book, archaeological journalist David Keys dramatically reconstructs the global chain of revolutions that began in the catastrophe of A.D. 535, then offers a definitive explanation of how and why this cataclysm occurred on that momentous day centuries ago. -- dead link