And because some parts of the core are hotter than others the core spins. Because the core circulates the iron makes a magnetic field around our Earth. Well, the Earth is really like alive, see. The core spews out hot rock and gas, this causes volcanos. The volcanos make mountains.
Weather wears down the by erosion.
And the Earth remains pretty dog gone livable. Long before environmentalists got on the band wagon, the Earth was re-cylcing. I have a boy friend there. I should call and see if he's alright. So, while the Earth had some heavy duty comet hits when it was new, most of the craters have been erased because of this plate tectonic recylcing.