Public release date: 3-Feb-2004 Contact: Dr Derek Ward-Thompson derek.ward-thompson@astro.cf.ac.uk 029-2087-5314 Cardiff University Astronomers unravel a mystery of the Dark Ages Undergraduates' work blames comet for 6th-century "nuclear winter" 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...