In 1908, on 30 June a roughly 120 meter space rock slammed into Earth's atmosphere causing an airburst equal to hundreds of atomic bombs. A few thousand square metres of forest was scorched and flattened.
The impact happened over the Russian river Tunguska in Siberia, in a very sparsely populated region. Without warning blinding flashed of light appeared in the sky, a burning wind was felt and loud thunder claps in quick succession. As the stony meteorite encountered the increasing resistance of air, it disintegrated, and caused a massive airburst 5-10 kilometers above the earth's surface. Several people were injured and later investigation concluded that Millions of trees had been flattened.
The airburst is estimated to have been around 10-15 Megatons TNT, which is 30 times the size of the Hiroshima atomic bomb. No crater was ever found.
Asteroid or Comet?
Scientists still aren't clear whether the impact was caused by an asteroid or a comet. A few fragments have been found, but none conclusive. An asteroid is a space rock consisting of usually dense material with iron or mineral rock fragments. A comet consists of ice, dust and gas, which likely all vaporised upon impact.