(Temporarily leapfrogging ancient civs to the start of the "Dark Ages"). In the mid 6th Century the world went through great upheaval. Based on work by David Keys, Part 1 explores the reasons for this, discovering 535 AD was an exceptionally bad year for trees, and the entire climate worldwide. Ice core samples reveal a sulphur spike in these years, which is traced back to Krakatoa erupting. Part 2 discusses the consequences, which are REALLY FASCINATING for the rise and fall of ancient civilisations across the world, the transition from Late Antiquity to the Middle Ages and the birth of modern religions.