Send in your answers with proof this happened before and could happen again. You'll get your information listed below.
- (Mr. Williamson). An Asteroid Hit. Large collisions—with five kilometer objects—happen approximately once every ten million years. The last known impact of an object of 10 km or more in diameter was at the Cretaceous-Tertiary extinction event 65 million years ago.
- (Alex A). The Black Plague. Decimated Europe in only two years. Anywhere from 30 - 60 percent of the population was infected. It caused religious, social, and economic upheavals. Historians estimate it took 150 years for Europe to recover fully.
- (Jaden F) Noah's Ark! You know, that huge flood waaaaaaaay back in the day, when Noah had to build an ark. =D Pretty good, eh? ;)