Heavy iron sank into the center of our world, releasing enough heat to melt the planet into a seething ball of lava. The thin crust of solid rock that floated on the surface was repeatedly beaten by massive meteor strikes. One impact came close to destroying the Earth -- splattering it into pieces that would settle together to create the moon.
Drop by drop, impacting comets and asteroids delivered water to the Earth, slowly filling the oceans and creating the we live in today.
But on the ground, it would have been a very strange place. A hostile atmosphere of ammonia, methane and carbon dioxide would have been impossible to breathe.