The Tunguska explosion

At 7:17 a.m. on the morning of June 30,1908, there was a mysterious explosion in the skies over Siberia. One theory is that it was caused by the impact of a large meteorite, about 6 km above the earth. Because the object exploded up in the atmosphere, instead of hitting the ground, it left no crater. The effect on the ground was limited to the devastation of a large forest. At the centre of the impact tree branches were stripped, leaving trunks standing up. But at distances from 5 to 15 km, the trees were blown over, lying with tops pointed away from the blast. 

No one was close to the blast. The closest humans were probably people camping in tents roughly 30 km from the explosion.

In 1945 a new theory about Tunguska was suggested. Aleksander Kazantsev was one of the first Russian scientists to evaluate the atomic bomb explosion at Hiroshima, Japan. He was also intrigued by the mystery of the Tunguska blast and quickly found connections between the two. The strange forest of trees, stripped of branches, but still standing, was found at Hiroshima too. The American atomic bomb had exploded at high altitude and the downward rushing shock wave had left the trees directly beneath standing, while flattening trees and houses further out in a radiating pattern. Kazantsev was the first to suggest that the event was caused by the explosion of an atomic-powered spaceship. While most scientists laughed at this explanation, some took his suggestion seriously and they began to notice other similarities.

This included apparent effects from radiation. Both the reindeer population at Tunguska and the human population at Hiroshima developed similar skin diseases. There was also evidence of accelerated plant growth at both locations.