On June 30th 1908 something apparently exploded over a place in central Siberia in Russia at a remote place called Tunguska. And that was no small explosion. The recorded history faced the largest cosmic event. Some say that it may have been a meteor. And everybody would agree but there is actually no impact crater.
Anyway something had exploded about five and a half miles up in the air (estimates range from 2 to 9 miles) with a force of (10 to 40) megatons, 500 to 2000 times the force of the Hiroshima explosion. The trees in a radius of at least 30 miles were downed. And the forest which was closest to the epicenter ignited in a pillar of flame seen hundreds of miles away.
For a better perspective, people living in Vanavara (70 miles away) were knocked down by the shock wave. In fact there were reports of horses being knocked down 400 miles away. In many remote places shock waves were recorded: Irkutsk (893 miles away), Tashkent, Tbilisi, and Jena. In addition to pressure disturbances, a local magnetic storm was recorded in Irkutsk that lasted for more than 4 hours. And they were similar to those caused by a high or medium altitude atomic detonation.
Many places in Eurasia reported abnormal light effects mainly on the nights of June 29th and 30th. The night sky in eastern Siberia was bright enough for you to read a newspaper. After 19 years an expedition was mounted to the remote area by a Russian Scientist named Leonid Kulik, and they found no crater. The result of the explosion is acceleration of the growth of biomass (the total mass of living matter within a unit of environmental area). Things here are growing at an accelerated rate with an increase in biological mutations.
Later in the 60's investigators found 4 smaller epicenters supposed to have been caused by individual explosions. They report that there were one huge explosion 5 miles up and several smaller explosions closer to the ground but still in the air.
And the information gathered shows that people in different areas didn't see the same thing - suggesting more than one object.
And in fact there was a man who did not survive the explosion with his house knocked down and the trees on fire. The man himself died of an illness with the symptoms of radiation poisoning two weeks later. At the place of the explosion the radiation is no more than background radiation today with a slight increase near the epicenter.
There are still some speculations as to even the direction the object traveling as eye witness accounts of the trajectory vary from the path indicated by the felled trees in the area. There are also plenty of theories about the explosion itself: from the meteor or comet theory, to miniature black holes, to antimatter, to an accidental detonation of an alien spacecraft, to a death ray tested by Tesla supposedly around this time.
But still there is no feasible explanation.