A British author named David Keys has written a book etitled "Catastrophe" which hypothesizes that the volcano Krakatoa exploded/erupted in 535 A.D., causing a sort of natural "nuclear" winter. I learned about this book by watching the PBS series "Secrets of the Dead". Keys ruled out asteroids or comets as the cause based upon ice cores from the Artic which contained high amounts of sulphur from around 535 A.D. According to the Javanese (?) Book of Kings (reportedly) Krakatoa erupted splitting the island of Java into the islands of Sumatra and Java.
"A British author named David Keys has written a book etitled "Catastrophe" which hypothesizes that the volcano Krakatoa exploded/erupted in 535 A.D., causing a sort of natural "nuclear" winter. " I read this book some time back. I don't recommend it. I do recommend Cosmic Winter by Clube and Napier and Exodus To Arthur by Mike Baillie.
The 'long-ring' tree ring data has recorded five catastrophic events in the last 10k years, they are, 3195BC, 2354BC, 1628BC, 1159BC, and 540BC with two minor events at 207BC and 44BC. The 540AD event is the only one that does not have an acid layer in the ice cores, that is why Bailey, Clube, Napier and Baillie speculate that it has/had a celestial element, a comet/asteroid.