I recently watched something very interesting in class. I don't know if it's true because it's just a theory, but basically it's like this. The earth's core is expanding and cooling, it's just the natural process, and after some time when it'll have cooled down completely and stopped rotating, the earth will die and become a dead mass of just rock basically. They explained in the documentary that this is exactly how Mars is and I started thinking about how Mars might have already had life millions of years ago and that the way it is now is just the result of the core dying. I thought that was pretty interesting to think about. But it's just a theory, but it would make sense I guess.