According to earlier models Earth should have crashed into Venus. Why not? It's theorized that an additional planet existed. This extra gas planet was ejected from the solar system, but helps explain why the trajectory of Earth didn't send it crashing into Venus.
A look at what our solar system may have looked like 3.8 billion years ago when icy debris floated between planets, Saturn's rings weren't yet fully formed, and an extra planet that has since been ejected danced with Saturn and Jupiter.
Recent updates to the Nice Planetary model help explain how the gas giants– Jupiter, Saturn, Neptune and Uranus–were able to so quickly attain their size. This current theory postulates that 3.5-4 billion years ago the planets were much closer together, and they lacked the standard orbits they have today leading to a lot of jostling. As the early gas giants moved, they were able to collect the debris that were thickly distributed in the younger solar system, with Jupiter even stealing some that would otherwise have allowed Mars to become larger. According to Science News', "The giant planets may have tumbled outward from the sun during their formation, growing like rolling snowballs as material was collected along the way."
