Differentiation The lesson is that material falling downward releases potential energy, and when it comes to rest at the end, the net effect is the production of heat. Let's now take this to the limit, by imagining an early Earth in which the composition is uniform, with a random intersprinkling of iron, silicon, oxygen, nickel, and all the other elements in a complex set of minerals. Now imagine the denser materials -- the iron and nickel, predominantly -- 'falling' towards the centre of the Earth, with the lighter elements being displaced upwards. This would produce fantastic amounts of heat-- after all, there are many trillions of tons of iron and nickel in the Earth, and they will settle like the Titanic, but this time through distances of thousands of kilometers. This differentiation is in fact a principal contributor to the present central heat of the Earth. The net effect of this is that the Earth would become -- and indeed did become! -- strongly differentiated. A body that was originally uniform in composition, like a scoop of chocolate ice
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