On the morning of June 30, 1908, a fireball cascaded down the Siberian sky and exploded with 2000 times the force of the nuclear blast that devastated Hiroshima, Japan. Weighing some 100,000 metric tons, the cosmic missile cut into the atmosphere and shattered in a rapid series of bursts, felling trees and incinerating an area of 2150 square miles - now known as the Tunguska "event." In the spring of 1992, Roy Gallant was invited by the Siberian branch of the National Academy of Sciences to take part in the annual Tunguska Expedition, to investigate this largest meteorite explosion in human history. The first American to participate in this expedition, Gallant thus began his mission as meteorite hunter. From Tunguska, he has since explored the major impact craters of Russia, including: Sikhote-Alin, a strewn field site infested with venomous snakes, brown bears, and Siberian tigers; the site of the famous Pallas Meteorite (namesake for the pallasite class of meteorites); and the enormous Popigai crater. Exploded some 30-40 million years ago, the Popigai crater is 100 kilometers in diameter, similar to the Chicxulub crater event that wiped out the dinosaurs in a planet-wide catastrophe