We are fortunate to live in a geologically stable period. In 535 AD, a supervolcano blew away one island in the Philipines creating an 18-month nuclear winter world wide. However, that's small potatoes compared to what this planet has been through. We have enjoyed about 12,000 years of relative comfort after the last period of glaciation. This brief warm period is predicted to go away in another 10,000 years. The further you go back in time, the more extreme some of the events have been, including at least five mass extinctions. One of these was caused by an asteroid strike and another may have been caused by a deadly gamma-ray burst from space. Twice, the planet has frozen solid, covered in a mile or more of ice worldwide. In the very early days of planet Earth, a Mars-sized object hit the Earth scooping out enough material to create the moon.