"On 30 June 1908, a powerful blast ripped open the sky near the Podkamennaya Tunguska River in Russia and flattened more than 2,000 square kilometers of forest. Eyewitnesses described a large object tearing through the atmosphere and exploding before reaching the ground, sending a wave of intense heat racing across the countryside. At an estimated three to five megatons of TNT equivalent, it was the biggest impact event in recorded history." (Mark Pelow, author of "Rock Samples Suggest Meteor Caused Tunguska Blast")

When the atomic bombs were used against Hiroshima and Nagasaki in August 1945, they ushered in a new era of power so destructive that nuclear weapons have not been used in any combat since then. The pictures of the devastated cities demonstrated the sheer strength of such weapons, and the impact was alarming enough to lead to efforts not only to control the proliferation of such weapons but to denuclearize altogether.

It was hard for people to comprehend the power behind nuclear weapons in 1945, but that was due in great measure to the fact that most people were unfamiliar with the Tunguska event, which took place over 35 years earlier in a sparsely populated region of Siberia. On June 30, 1908, an explosion with an epicenter near the Tunguska River flattened an area of about 2,000 square miles, destroying tens of millions of trees and killing countless numbers of wildlife. Miraculously there were no recorded human casualties as a result of the since-named Tunguska event, which generated the energy equivalent of 1,000 of the atomic bombs dropped on Hiroshima. The shockwave alone would have measured 5.0 on the Richter scale.