[kennedy]

I have never understood one aspect of the primordial dust cloud theory of planetary formation.

This may be a really stupid question, but why are various elements contained in deposits and veins? I don't see any reason why iron, uranium, gold and other mineral atoms would gravitate toward each other. I would think that elements would be fairly evenly mixed.

[Gumption]

I'm pretty sure that all matter has gravity. The larger, or more dense, the mass, the more gravity it has. But I'm just a plumber, so let's ask the main man himself ... Mr. Radio.

[Batrachian]

What you have to realize is that the ore deposits as we find them today are not just as they where right after the planet formed. They're the result of billions of years of geological activity. They've been moved around by plate tectonics, mixed and melted by magma, and shuffled and reshuffled over and over again since the planet first formed.

I'm not a geologist, but I think heavy metals tend to gravitate towards each other in the semi-liquid mantle of the planet because they have similar densities, and so tend to move around in the slow convection currents of the mantle in similar ways.

In short, what you see now reflects not the primordial dust cloud that the Earth formed from, but an Earth molded by billions of years of geological activity.