Okay, I heard some theory that the Earth formed at the asteroid belt and was smacked by something big and moved closer to the sun leaving behind the asteroids. <br /><br />The counter to this theory is that the asteroids never formed a planet because of Jupiter's gravity. That assumes Jupiter was a huge planet before the asteroids failed to form a planet. I dont see the logic in that, I'd think planets closer in form first since they're in a more dense part of the nebula. <br /><br />Is it true some asteroids show evidence of "differentiation" as if they were part of a planet? I understand astronomers do believe the Earth was hit by something big in the past, maybe ~4 billion years ago. Is it logical the Earth suffered such a collision and remained in the same orbit?