After years of being unsure, scientists have confirmed what caused the Tanguska Event:
Victor Kvasnytsya from the National Academy of Sciences of Ukraine and his colleagues used the latest imaging and spectroscopy techniques to identify aggregates of carbon minerals—diamond, lonsdaleite, and graphite. Lonsdaleite in particular is known to form when carbon-rich material is suddenly exposed to a shock wave created by an explosion, such as that of a meteorite hitting Earth. The lonsdaleite fragments contain even smaller inclusions of iron sulphides and iron-nickel alloys, troilite and taenite, which are characteristic minerals found in space-based objects such as meteorites. The precise combination of minerals in these fragments point to a meteorite source. It is near-identical to similar minerals found in an Arizona impact.
The samples point to one thing: the Tunguska impact is the largest meteorite impact in recorded history.US researchers have estimated that the Tunguska blast could have been as much as the equivalent of a five megaton TNT explosion—hundreds of times more powerful than the Hiroshima blast. The meteorite tore apart as it entered the atmosphere at an angle, so that little of it reached the ground intact. That is why all that remains are such small specks that have been fossilised in the Siberian peat.