Pop history tells us that the explosion in a remote section of Siberia in 1908 was the result of a meteor which left no trace. The explosion left radiation residue and the blast was identical to 1945 American nuclear tests. Secietific geniuses were in no short supply in the late 1800's and a New Zealand scientist was experimenting in nuclear energy in the UK in the early 1900's. Nobody knows what was going on in the relatively closed society of Russia in the early 1900's and it is reasonabe to suspect that a nuclear test lab located in a remote area might have gone up in the first big one. It's a better theory than a meteor which conveniently picked remote Siberia instead of New York City and left no trace.