Ever since our planet's birth around 4.5 billion years ago its been hit by asteroids more times than therere people on Earth today. While most of them burn out and shrink on entry in our atmosphere, there are a few asteroids that have done some fair damage, none of which come close to the dino killer. About 65 million years ago a 5-15 km across asteroid hit the planet, starting a chain reaction of earthquakes, burning debris flying everywhere, and fire raining from the sky. Put all that together, and you have an extinction level firestorm surging throughout the whole planet, culminating in a global warming that annihilates the dinosaurs leaving only about 20% of all life left on Earth. The funny thing here is, had it not been for that asteroid, mammals probably wouldve never climbed the food chain, and the human race mightve never come to be. Thankfully, today astronomers are watching the skies for any potential killers coming our way.