Just after 7 am on June 30th, 1908, a blinding light filled the sky around the Podkamennaya Tunguska River in Central Siberia. An Irkutsk newspaper stated that area peasants saw a body of light too bright to gaze at with the naked eye. The glow was white-blue in color and formed a cylinder that went up into the sky. Buildings shook and flames went up into the clouds. The explosion flattened 80 million trees over an 830 square mile area.
But, what caused the blast? A number of theories have been suggested. Some think that the blast was caused by a device that inventor Nikola Tesla said he was working on that would transmit energy wirelessly through the air. Proponents of that theory say that Tesla was researching largely deserted areas of Siberia.
Others have hypothesized that the blast was an early nuclear test. Russian science fiction author Aleksandr Kazantsev was among the first to float this theory back in 1946. In the 1970s, conspiracy theorists added the suggestion that an alien spacecraft, propelled by nuclear power, exploded in the area.
These days, however, the most popular theory is that the blast was caused by a comet that entered the earth’s atmosphere. Astronomers say that a comet that was made of ice and dust would have been vaporized on impact, leaving little behind. And, the theory is supported by the glowing skies that were observed across Europe for several evenings after impact, which could have been caused by dispersing ice and dust.
Although more than 1000 papers have been written about possible causes, there is no way to tell for sure. Speculation about the blast continues more than a century after the fact.