If our solar system originated from the same dust / gas cloud, why do we see such differences in abundance of elements from one body to another. I can come up with two possible answers: 1. Rotation of cloud centrifuged heavier elements towards edge (Almost certainly not true, because it would need to overcome gravity, and composition of solar system bodies does not follow that pattern) 2. At some point in solar system formation original dust cloud, which presumably consisted of mainly light elements, interacted with another material, probably much smaller in quantity, and different in origin. I am only guessing, so any help on this is welcome.