The Tunguska Event was an explosion that occurred in the skies above Eastern Siberia on 30 June 1908. The blast flattened around 700 square miles (2000 square kilometers) of forest. The lower end estimates for the force of the explosion are about 200 times that of the atomic bomb dropped on Hiroshima. The blast was probably the result of a meteor or comet exploding in the atmosphere a few miles above the Earth’s surface.
Fanciful and dubious alternative explanations for the event ranging from an impact by a small piece of antimatter to a crashed alien spaceship have been put forth.
When Russian mineralogist Leonid Kulik led an expedition to the area in 1927, the damage was still evident.
The Tunguska Event has been incorporated into numerous works of science fiction. It has also served as a cautionary reminder that Earth has been and will continue to be periodically struck by large extraterrestrial objects like asteroids that have the potential to cause severe damage to both civilization and the environment, including triggering mass extinction events.
Developing the technological capability of detecting and diverting objects massive enough to cause planetary devastation is something that will, sooner or later, be necessary if global catastrophe is to be averted.