If I first see a tree in the winter, I might assume that it is not a fruit-tree. But when I return in the summer to find it covered with plums, I must exclaim, 'Excuse me! You were a fruit-tree after all.' Imagine, then, that a billion years ago some beings from another part of the galaxy made a tour through the solar system in their flying saucer and found no life. They would dismiss it as 'Just a bunch of old rocks!' But if they returned today, they would have to apologize: 'Well - you were peopling rocks after all!' You may, of course, argue that there is no analogy between the two situations. The fruit-tree was at one time a seed inside a plum, but the earth - much less the solar system or the galaxy - was never a seed inside a person. But, oddly enough, you would be wrong.