On the morning of June 30, 1908 a huge object flew out of the sky and exploded over Tunguska in Siberia. The sky was reported to have split in half because of the blast. A flaming object was reported trailing dust. The explosion shook the ground, shattered windowpanes, and caused a searing wind to race across the landscape and knock trees down. 1,200 square miles of forest were set on fire by the event. Later estimates by scientists place the force of the blast as equivalent to a 20 megaton nuclear device.

A multitude of explanations exist for the Tunguska incident. Antimatter might have leaked into our universe from an alternate one. The antimatter reacted very violently when it contacted regular matter. A extremely small black hole might have collided with the Earth triggering the explosion. A UFO might have disintegrated in the atmosphere. Russian officials reported finding high radioactivity, possibly from an alien craft's propulsion system, in the soil near the blast. Calculations show that the object deacclerated after entering the atmosphere. The occupants of the craft might have been attempting a landing or deliberately avoiding crashing into a populated area. A comet or asteroid is another possible answer to the question of what caused the explosion.