A series of strange events occurred on that last day of June. A trainload of passengers on the trans-Siberian railway noticed a giant fiery streak dominating the day sky and descending alarmingly fast to the ground. The Evenki nomad tribe 350 miles to the north saw what looked like a giant sun racing across the distant sky and then exploding with an unimaginable intensity, with a shockwave strong enough to knock over buildings and send horses fleeing in terror. Residents as far away as London noted the sky took on an unusual purplish color that day.

On this day, June 30, in 1908, a comet or a meteor of a substantial size entered the earth’s atmosphere and fell down to the surface, exploding just before impact at an altitude of 3-6 miles. Nearby witnesses reported seeing a mushroom cloud, and indeed the explosion could be compared in power to the atomic bombs dropped on Hiroshima and Nagasaki — except the Tunguska explosion was 1,000 times more powerful.

It was humanity’s fortune that the impact happened over an uninhabited area of Siberia. Had the dimensions of the impact — a 9-mile radius completely incinerated; a shockwave strong enough to fell trees for over 800 miles; an earthquake likely measuring around 5.0 — been over a large metropolitan area, the damage could have been far greater. This was the largest impact over land in recorded history.