Tunguska, Russia, July 30, 1908

References

National Geographic - http://news.nationalgeographic.com/news/2007/11/071107-russia-crater.html

Wikipedia - http://en.wikipedia.org/wiki/Tunguska_event

Mark W. Brazo and Steven A. Austin - http://www.grisda.org/origins/09082.htm and  http://www.icr.org/research/index/researchp_sa_r05/

Rotten.com - http://www.rotten.com/library/history/nature/natural-disasters/tunguska/

http://www.msnbc.msn.com/id/5686713