The Tunguska explosion levelled over 2,000 square kilometres of Siberian forest, an area equivalent to Greater London. Subsequent surveys showed the area of destruction to be butterfly-shaped.

Dust was found with an unusually high concentration of iridium. Iridium is chemical element 77. It is very hard and brittle, making it very hard to machine, form, or work. It is the most corrosion resistant metal known.

"It is also worth noting that anomalous deposits of iridium can be found throughout the world at the 65 million year old interface between rocks of the cretaceous and tertiary eras. Such concentrations, thousands of times greater than that normally found in the Earth's crust, are believed to have arrived extra-terrestrially. Their presence is held up as evidence by supporters of the theory that a massive asteroid collision with our planet was the cause of the extinction of the dinosaurs at that same point in geological time".

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