Around 65 million years ago, an asteroid about six miles wide collided with Earth, leaving a crater about 105 miles wide in the Yucatan Peninsula and wiping out all dinosaurs. But some scientists believe an even larger object struck Earth around 4.5 billion years ago, when a planet called Theia, which was roughly the same size as Mars, collided with Earth. That collision – known as the Giant Impact Theory -- broke off several large chunks of both planets, one of which became our moon. An asteroid that hit Siberia in 1908 was about 120 feet wide – roughly the same length as a Boeing 737 – and had eyewitness accounts. Nicknamed the “Tunguska event” after a nearby Siberian river, the asteroid actually exploded in the air at an altitude of about 28,000 feet. About 80 million trees were knocked over and people 40 miles away were shaken by the blast. Some large man-made objects have also hit Earth, including a 550-pound fuel tank from a NASA Delta II rocket that landed in a Texas field in 1997. A piece of insulation from the same rocket hit a woman in Oklahoma while she was out for a walk. Luckily, that woman wasn’t injured. Obviously, things could have gone far worse – just ask the dinosaurs that were around 65 million years ago. VIDEO