The explosion was even registered by an earthquake measuring station 2,485 miles away in St. Petersburg. Earthquake tremors were also recorded by more distant stations around the world. But at that time no one knew the cause of these tremors.
Q: How far did this happen from inhabited areas?
A: The explosion site was then so remote that it was not even accessible to local inhabitants, the Tungus people. The nearest witnesses to the explosion were at Vanavara, a small trading station some 40 miles from the explosion site.
Several miles north of Vanavara, dozens of nomads and herdsmen were thrown into the air and bruised. An elderly man hit a tree and broke his arm. Another elderly man died of fright. Thousands of reindeer belonging to four separate herds were killed as the pines and cedars around them blazed.
Q: How have theories about what happened evolved over time?
A: In 1908, Russia was a country caught in political unrest and social upheaval. Nothing was [studied] until 1927 when a Soviet scientist, Leonid Kulik, visited the explosion site. After three expeditions to the site, Kulik came to the conclusion that the Tunguska event was caused by a meteorite.
Since Kulik’s death in 1942, numerous scientific expeditions have been conducted to the explosion site, but no crater and no meteorite material from outer space has yet been found.
Q: What if it wasn't a meteorite?
A: The question fascinates scientists and science fiction writers. There are nearly 100 theories.
The lineup of suspects includes a comet, a mini-black hole, an asteroid, a rock of antimatter or a methane gas blast from below. More imaginative explanations include an alien spacecraft that exploded in mid-air and an experiment on a "death ray" which got out of hand.
My favorite theory is that the famous Krakatoa volcanic eruption in August 1883 generated strong radio waves, which were received 11 years later at the star 61 Cygni, 11 light-years away from us.