The Dark Ages?

Astronomers Unravel A Mystery Of The Dark Ages: Undergraduates' Work Blames Comet For 6th-century 'Nuclear Winter'

Science Daily — Scientists at Cardiff University, UK, believe they have discovered the cause of crop failures and summer frosts some 1,500 years ago a comet colliding with Earth.

The team has been studying evidence from tree rings, which suggests that the Earth underwent a series of very cold summers around 536-540 AD, indicating an effect rather like a nuclear winter.

The scientists in the School of Physics and Astronomy believe this was caused by a comet hitting the earth and exploding in the upper atmosphere. The debris from this giant explosion was such that it enveloped the earth in soot and ash, blocking out the sunlight and causing the very cold weather.

This effect is known as a plume and is similar to that which was seen when comet Shoemaker-Levy-9 hit Jupiter in 1995.

Historical references from this period - known as the Dark Ages are sparse, but what records there are, tell of crop failures and summer frosts.

The work was carried out by two Cardiff undergraduate students, Emma Rigby and Mel Symonds, as part of their student project work under the supervision of Dr Derek Ward-Thompson.

Their findings are reported in the February issue of Astronomy and Geophysics, the in-house magazine of the Royal Astronomical Society.

The surprising result of the new work is just how small a comet is needed to cause such dramatic effects. The scientists calculate that a comet not much more than half a kilometre across could cause a global nuclear winter effect. This is significantly smaller than was previously thought.

Dr. Ward-Thompson said: "One of the exciting aspects of this work is that we have re-classified the size of comet that represents a global threat. This work shows that even a comet of only half a kilometre in size could have global consequences. Previously nothing less than a kilometre across was counted as a global threat. If such an event happened again today, then once again a large fraction of the earth's population could face starvation."

The comet impact caused crop failures and wide-spread starvation among the sixth century population. The timing coincides with the Justinian Plague, widely believed to be the first appearance of the Black Death in Europe. It is possible that the plague was so rampant and took hold so quickly because the population was already weakened by starvation.

The exact nature and sequence of events in the mid-6th. century A.D. that gave rise to the period we refer to as the European ‘Dark Age’ is still a matter for speculation amongst historians and archæologists. Over the past 20 years or so, certain paleo-climatologists have begun comparing notes with archæologists and astronomers, and interestingly, in the absence of written records, many have begun to look a little more closely at mythology in their efforts to corroborate the findings of their researches. While much of this recent bout of inter-disciplinary brainstorming has focussed on the 6th.C. AD start of the European Dark Age, earlier dates are also of great interest to those embroiled in this veritable ‘paradigm shift’.

Beginning in the year A.D. 536, and continuing through until A.D. 545, the dendrochronology record reveals a dramatic ‘narrowest-rings event’ that is corroborated by some of the findings of the Greenland Ice Sheet Projects. There, a significant absense of any tell-tale volcanic ‘acid spike’ in the ice-cores record suggests an altogether different cause - dustloading of the stratosphere by minute particles of dust and other cometary debris.

Climatologists and astronomers concur that this event bears all the hallmarks of a 'cosmic winter’ scenario - when dust in the stratosphere blots out the Sun, lowering the global temperature, hindering plant growth and in so doing undermining agricultural societies.