MOSCOW, Russia (CNN) -- It produced a blast hundreds of times stronger than the Hiroshima bomb, was seen hundreds of miles away and narrowly missed obliterating an entire city -- but 100 years to the week after the mysterious explosion in Siberia, no one is any closer to understanding what caused it.
Millions of trees were destroyed by the Tunguska blast.
Despite countless investigations, the so-called Tunguska Event remains one of the 20th century's greatest enigmas -- seized upon by mystics, UFO enthusiasts and scientists as evidence of angry gods, extraterrestrial life or the impending threat of a cosmic collision.
But says Stanislav Krivyakov, who has spent the past 35 years investigating the Siberian blast, despite intense interest in the event -- which has featured in several episodes of "The X-Files" -- no conclusive evidence has been found to support any theory.
"There are many people who build their hypotheses based on scanty information," he told CNN.
"But there are many aspects to the phenomenon that don't fit any standards or analogies. In everything about it we find something complicated, problematic, vague. It's truly out of the ordinary."
Deepening the mystery was the delay in a full investigation into the event, which occurred as Russia was entering the years of upheaval that surrounded the communist revolution. Sound off: What do you think caused blast?
The first expedition to try to find the "Tunguska meteorite" did not take place until the late 1920s when a crater was drained resulting in the discovery of nothing more cosmic than an old tree stump. After World War II, searches resumed, but again proved fruitless.
And even though the effects of the blast wave that destroyed 80 million trees are still visible today, "meteoreticians," as some theorists are know, have found no point of impact to support their claim.
"Up to this day, not a single fragment of the Tunguska phenomenon, no cosmic substance has been found. That's the main reason why there isn't any even fundamental understanding (of the phenomenon) yet," said Boris Mushailov, a professor at the Sternberg Astronomical Institute in Moscow.
Mushailov was one of the organizers of an international conference last week at the Russian Academy of Sciences devoted to the Tunguska Event.
He said he leans toward a "comet theory," explaining that an object could have entered Earth's atmosphere and burst into pieces up to 10 kilometers above the Tunguska river -- causing the giant explosion -- but scattering the object into smaller debris most of which burned up.
So-called "alternativists," however, reject the meteor and comet theories, because of the lack of a major crater or fragments.
Their search for more unlikely explanations has led to the site becoming a Mecca for UFO enthusiasts, spawning a Tunguska meteorite museum and scores of photographs of what are claimed to be parts of extra terrestrial craft discovered in the area.
As the debate rages on, many scientists say the Tunguska event could be a harbinger of a genuine scientific phenomenon that could spell disaster for life on Earth.
Researchers looking at the trajectories of asteroids say that if a large meteorite breached the planet's atmosphere once, then there is no guarantee history won't repeat itself.
"The Earth all along its evolution has collided with various cosmic objects, from 1 millimeter to a kilometer in size," Mushailov said.
"One measuring 10 to a hundred meters causes a local catastrophe. And of course, not a single method of protection exists so far," he said.
Scientists estimate if the Tunguska explosion had happened four hours later over St. Petersburg, the city would have ceased to exist, resulting in the deaths of hundreds of thousands of people.
As it was, the village of Vanavara, which at a distance of 70 kilometers was the closest settlement to blast, survived.
To mark the 100th anniversary of its lucky escape, Vanavara has repainted its buildings in vivid "meteoric" colors, and is unveiling a new monument -- a colorful sphere symbolizing a cosmic body.
Not to offend the "alternativists," locals also built a marker by the blast spot resembling a sacred bird or a UFO.
But ordinary Vanavarans say they wish scientists would stop searching for meteors and Martians and instead search for gas or oil that could bring much-needed money to the area.
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