At 7:14 a.m. on June 30, 1908, a giant explosion shook central Siberia. Witnesses close to the event described seeing a fireball in the sky, as bright and hot as another sun. Millions of trees fell and the ground shook. Although a number of scientists investigated, it is still a mystery as to what caused the explosion.

The Blast

The explosion is estimated to have created the effects of a magnitude 5.0 earthquake, causing buildings to shake, windows to break, and people to be knocked off their feet even at 40 miles away.

The blast, centered in a desolate and forested area near the Podkamennaya Tunguska River in Russia, is estimated to have been a thousand times more powerful than the bomb dropped on Hiroshima.

The explosion leveled an estimated 80 million trees over an 830 square-mile area in a radial pattern from the blast zone. Dust from the explosion hovered over Europe, reflecting light that was bright enough for Londoners to read at night by it.

While many animals were killed in the blast, including hundreds of local reindeer, it is believed that no humans lost their lives in the blast.

Examining the Blast Area

The blast zone's remote location and the intrusion of worldly affairs (World War I and the Russian Revolution) meant that it wasn't until 1927 -- 19 years after the event -- that the first scientific expedition was able to examine the blast area.

Assuming that the blast had been caused by a falling meteor, the expedition expected to find a huge crater as well as pieces of the meteorite. They found neither. Later expeditions were also unable to find credible evidence to prove the blast was caused by a falling meteor.

Cause Of the Explosion

In the decades since this huge explosion, scientists and others have attempted to explain the cause of the mysterious Tunguska Event. The most commonly accepted scientific explanation is that either a meteor or a comet entered the Earth's atmosphere and exploded a couple of miles above the ground (this explains the lack of impact crater).

To cause such a large blast, some scientists determined that the meteor would have weighed around 220 million pounds (110,000 tons) and traveled approximately 33,500 miles per hour before disintegrating. Other scientists say that the meteor would have been much larger, while still others say much smaller.

Additional explanations have ranged from the possible to the ludicrous, including a natural gas leak escaped from the ground and exploded, a UFO spaceship crashed, the effects of a meteor destroyed by a UFO's laser in an attempt to save Earth, a black hole that touched Earth, and an explosion caused by scientific tests done by Nikola Tesla.

Still a Mystery

Over a hundred years later, the Tunguska Event remains a mystery and its causes continue to be debated.

The possibility that the blast was caused by a comet or meteor entering the Earth's atmosphere creates additional worry. If one meteor could cause this much damage, then there is a serious possibility that in the future, a similar meteor could enter Earth's atmosphere and rather than landing in remote Siberia, land on a populated area. The result would be catastrophic.