Watch History Channel Documentaries online: Episode 45 Siberian Apocalypse

This astounding documentary delves into the mysteries of the Tunguska event – one of the largest cosmic disasters in the history of civilisation. At 7.15 am, on 30th June 1908, a giant fireball, as bright the sun, exploded in the sky over Tunguska in central Siberia. Its force was equivalent to twenty million tonnes of TNT, and a thousand times greater than that of the atomic bomb dropped on Hiroshima in 1945. An estimated sixty million trees were felled over an area of over two thousand square kilometres - an area over half the size of Rhode Island. If the explosion had occurred over London or Paris, hundreds of thousands of people would have been killed. For almost one hundred years, the catastrophic cosmic impact of the century has remained a terrifying and hotly debated mystery. The first expedition to reach the site was led by Russian scientist L.A. Kullik in 1938. His team uncovered a colossal degree of devastation, but could find no obvious crater. Historians and scientists continue to speculate about what caused the apocalyptic fire in the sky, and why the elusive object failed to leave a crater. A huge number of theories and conspiracies surround the event. The suggested culprits vary from asteroids and comets to ball lightning, black holes and alien spaceships. Most scientists agree that such an event is likely to occur again. Next time, the human toll could be unimaginable. We reveal that NASA and other organisations are currently engaged in a desperate race against time to stop the next potential planet killer.

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